How do I get a TextBox to only accept numeric input in WPF

Question

I m looking to accept digits and the decimal point  but no sign   I ve looked at samples using the NumericUpDown control for Windows Forms  and this sample of a NumericUpDown custom control from Microsoft  But so far it seems like NumericUpDown  supported by WPF or not  is not going to provide the functionality that I want  The way my application is designed  nobody in their right mind is going to want to mess with the arrows  They don t make any practical sense  in the context of my application   So I m looking for a simple way to make a standard WPF TextBox accept only the characters that I want  Is this possible  Is it practical

User · Answer

For developers who want their text fields to accept unsigned numbers only such as socket ports and so on:

WPF

<TextBox PreviewTextInput="Port_PreviewTextInput" MaxLines="1"/>

C#

private void Port_PreviewTextInput(object sender, TextCompositionEventArgs e)
{
    e.Handled = !int.TryParse(e.Text, out int x);
}

User · Answer

I was working with an unbound box for a simple project I was working on  so I couldn t use the standard binding approach  Consequently I created a simple hack that others might find quite handy by simply extending the existing TextBox control   namespace MyApplication InterfaceSupport       public class NumericTextBox   TextBox                 public NumericTextBox     base                         TextChanged    OnTextChanged                      public void OnTextChanged object sender  TextChangedEventArgs changed                        if   String IsNullOrWhiteSpace Text                                 try                                       int value   Convert ToInt32 Text                                     catch  Exception e                                        MessageBox Show String Format   0  only accepts numeric input    Name                        Text                                                           public int  Value                       set                               if  value    null                                        this Text   value ToString                                      else                      Text                                 get                               try                                       return Convert ToInt32 this Text                                     catch  Exception ef                                           Not numeric                                    return null                                    Obviously  for a floating type  you would want to parse it as a float and so on  The same principles apply   Then in the XAML file you need to include the relevant namespace    lt UserControl x Class  MyApplication UserControls UnParameterisedControl                 Snip                xmlns interfaceSupport  clr-namespace MyApplication InterfaceSupport                gt    After that you can use it as a regular control    lt interfaceSupport NumericTextBox Height  23  HorizontalAlignment  Left  Margin  168 51 0 0  x Name  NumericBox  VerticalAlignment  Top  Width  120   gt

User · Answer

For those looking for a quick and very simple implementation for this type of problem using only integers and decimal  in your XAML file  add a PreviewTextInput property to your TextBoxand then in your xaml cs file use   private void Text PreviewTextInput object sender  TextCompositionEventArgs e        e Handled    char IsDigit e Text Last     amp  amp   e Text Last               It s kind of redundant to keep checking the entire string every time unless  as others have mentioned  you re doing something with scientific notation  albeit  if you re adding certain characters like  e   a simple regex adding symbols characters is really simple and illustrated in other answers   But for simple floating point values  this solution will suffice   Written as a one-liner with a lambda expression   private void Text PreviewTextInput object sender  TextCompositionEventArgs e    gt  e Handled    char IsDigit e Text Last    amp  amp   e Text Last

User · Answer

Use   Private Sub DetailTextBox PreviewTextInput      ByVal sender As Object      ByVal e As System Windows Input TextCompositionEventArgs      Handles DetailTextBox PreviewTextInput      If  IsANumber Then         If Not Char IsNumber e Text  Then             e Handled   True         End If     End If End Sub

User · Answer

Another approach will be using an attached behavior  I implemented my custom TextBoxHelper class  which can be used on textboxes all over my project  Because I figured that subscribing to the events for every textboxes and in every individual XAML file for this purpose can be time consuming   The TextBoxHelper class I implemented has these features    Filtering and accepting only numbers in Double  Int  Uint and Natural format Filtering and accepting only Even or Odd numbers Handling paste event handler to prevent pasting invalid text into our numeric textboxes Can set a Default Value which will be used to prevent invalid data as the last shot by subscribing to the textboxes TextChanged event   Here is the implementation of TextBoxHelper class   public static class TextBoxHelper        region Enum Declarations      public enum NumericFormat               Double          Int          Uint          Natural            public enum EvenOddConstraint               All          OnlyEven          OnlyOdd             endregion       region Dependency Properties  amp  CLR Wrappers      public static readonly DependencyProperty OnlyNumericProperty           DependencyProperty RegisterAttached  OnlyNumeric   typeof NumericFormat    typeof TextBoxHelper               new PropertyMetadata null  DependencyPropertiesChanged        public static void SetOnlyNumeric TextBox element  NumericFormat value    gt          element SetValue OnlyNumericProperty  value       public static NumericFormat GetOnlyNumeric TextBox element    gt           NumericFormat  element GetValue OnlyNumericProperty         public static readonly DependencyProperty DefaultValueProperty           DependencyProperty RegisterAttached  DefaultValue   typeof string   typeof TextBoxHelper               new PropertyMetadata null  DependencyPropertiesChanged        public static void SetDefaultValue TextBox element  string value    gt          element SetValue DefaultValueProperty  value       public static string GetDefaultValue TextBox element    gt   string  element GetValue DefaultValueProperty         public static readonly DependencyProperty EvenOddConstraintProperty           DependencyProperty RegisterAttached  EvenOddConstraint   typeof EvenOddConstraint   typeof TextBoxHelper               new PropertyMetadata EvenOddConstraint All  DependencyPropertiesChanged        public static void SetEvenOddConstraint TextBox element  EvenOddConstraint value    gt          element SetValue EvenOddConstraintProperty  value       public static EvenOddConstraint GetEvenOddConstraint TextBox element    gt           EvenOddConstraint element GetValue EvenOddConstraintProperty         endregion       region Dependency Properties Methods      private static void DependencyPropertiesChanged DependencyObject d  DependencyPropertyChangedEventArgs e                if    d is TextBox textBox               throw new Exception  Attached property must be used with TextBox              switch  e Property Name                        case  OnlyNumeric                                 var castedValue    NumericFormat   e NewValue                   if  castedValue HasValue                                        textBox PreviewTextInput    TextBox PreviewTextInput                      DataObject AddPastingHandler textBox  TextBox PasteEventHandler                                     else                                       textBox PreviewTextInput -  TextBox PreviewTextInput                      DataObject RemovePastingHandler textBox  TextBox PasteEventHandler                                      break                             case  DefaultValue                                 var castedValue    string  e NewValue                   if  castedValue    null                                        textBox TextChanged    TextBox TextChanged                                    else                                       textBox TextChanged -  TextBox TextChanged                                     break                                      endregion      private static void TextBox PreviewTextInput object sender  TextCompositionEventArgs e                var textBox    TextBox sender           string newText           if  textBox SelectionLength    0                        newText   textBox Text Insert textBox SelectionStart  e Text                     else                       var textAfterDelete   textBox Text Remove textBox SelectionStart  textBox SelectionLength                newText   textAfterDelete Insert textBox SelectionStart  e Text                      var evenOddConstraint   GetEvenOddConstraint textBox            switch  GetOnlyNumeric textBox                         case NumericFormat Double                                if  double TryParse newText  out double number                                         switch  evenOddConstraint                                                case EvenOddConstraint OnlyEven                               if  number   2    0                                  e Handled   true                              else                                 e Handled   false                               break                           case EvenOddConstraint OnlyOdd                               if  number   2    0                                  e Handled   true                              else                                 e Handled   false                               break                                                          else                     e Handled   true                   break                             case NumericFormat Int                                if  int TryParse newText  out int number                                         switch  evenOddConstraint                                                case EvenOddConstraint OnlyEven                               if  number   2    0                                  e Handled   true                              else                                 e Handled   false                               break                           case EvenOddConstraint OnlyOdd                               if  number   2    0                                  e Handled   true                              else                                 e Handled   false                               break                                                          else                     e Handled   true                   break                             case NumericFormat Uint                                if  uint TryParse newText  out uint number                                         switch  evenOddConstraint                                                case EvenOddConstraint OnlyEven                               if  number   2    0                                  e Handled   true                              else                                 e Handled   false                               break                           case EvenOddConstraint OnlyOdd                               if  number   2    0                                  e Handled   true                              else                                 e Handled   false                               break                                                          else                     e Handled   true                   break                             case NumericFormat Natural                                if  uint TryParse newText  out uint number                                         if  number    0                          e Handled   true                      else                                               switch  evenOddConstraint                                                        case EvenOddConstraint OnlyEven                                   if  number   2    0                                      e Handled   true                                  else                                     e Handled   false                                   break                               case EvenOddConstraint OnlyOdd                                   if  number   2    0                                      e Handled   true                                  else                                     e Handled   false                                   break                                                                                    else                     e Handled   true                   break                                     private static void TextBox PasteEventHandler object sender  DataObjectPastingEventArgs e                var textBox    TextBox sender           if  e DataObject GetDataPresent typeof string                          var clipboardText    string  e DataObject GetData typeof string                 var newText   textBox Text Insert textBox SelectionStart  clipboardText                var evenOddConstraint   GetEvenOddConstraint textBox                switch  GetOnlyNumeric textBox                                 case NumericFormat Double                                        if  double TryParse newText  out double number                                                 switch  evenOddConstraint                                                        case EvenOddConstraint OnlyEven                                   if  number   2    0                                      e CancelCommand                                     break                               case EvenOddConstraint OnlyOdd                                   if  number   2    0                                      e CancelCommand                                     break                                                                      else                         e CancelCommand                         break                                     case NumericFormat Int                                        if  int TryParse newText  out int number                                                 switch  evenOddConstraint                                                        case EvenOddConstraint OnlyEven                                   if  number   2    0                                      e CancelCommand                                     break                               case EvenOddConstraint OnlyOdd                                   if  number   2    0                                      e CancelCommand                                      break                                                                      else                         e CancelCommand                         break                                     case NumericFormat Uint                                        if  uint TryParse newText  out uint number                                                 switch  evenOddConstraint                                                        case EvenOddConstraint OnlyEven                                   if  number   2    0                                      e CancelCommand                                     break                               case EvenOddConstraint OnlyOdd                                   if  number   2    0                                      e CancelCommand                                      break                                                                      else                         e CancelCommand                         break                                     case NumericFormat Natural                                        if  uint TryParse newText  out uint number                                                 if  number    0                              e CancelCommand                            else                                                       switch  evenOddConstraint                                                                case EvenOddConstraint OnlyEven                                       if  number   2    0                                          e CancelCommand                                         break                                   case EvenOddConstraint OnlyOdd                                       if  number   2    0                                          e CancelCommand                                         break                                                                                                    else                                               e CancelCommand                                               break                                                    else                       e CancelCommand                         private static void TextBox TextChanged object sender  TextChangedEventArgs e                var textBox    TextBox sender           var defaultValue   GetDefaultValue textBox            var evenOddConstraint   GetEvenOddConstraint textBox            switch  GetOnlyNumeric textBox                         case NumericFormat Double                                if  double TryParse textBox Text  out double number                                         switch  evenOddConstraint                                                case EvenOddConstraint OnlyEven                               if  number   2    0                                  textBox Text   defaultValue                               break                           case EvenOddConstraint OnlyOdd                               if  number   2    0                                  textBox Text   defaultValue                               break                                                          else                     textBox Text   defaultValue                   break                             case NumericFormat Int                                if  int TryParse textBox Text  out int number                                         switch  evenOddConstraint                                                case EvenOddConstraint OnlyEven                               if  number   2    0                                  textBox Text   defaultValue                               break                           case EvenOddConstraint OnlyOdd                               if  number   2    0                                  textBox Text   defaultValue                               break                                                          else                     textBox Text   defaultValue                   break                             case NumericFormat Uint                                if  uint TryParse textBox Text  out uint number                                         switch  evenOddConstraint                                                case EvenOddConstraint OnlyEven                               if  number   2    0                                  textBox Text   defaultValue                               break                           case EvenOddConstraint OnlyOdd                               if  number   2    0                                  textBox Text   defaultValue                               break                                                          else                     textBox Text   defaultValue                   break                             case NumericFormat Natural                                if  uint TryParse textBox Text  out uint number                                         if number    0                          textBox Text   defaultValue                      else                                               switch  evenOddConstraint                                                        case EvenOddConstraint OnlyEven                                   if  number   2    0                                      textBox Text   defaultValue                                   break                               case EvenOddConstraint OnlyOdd                                   if  number   2    0                                      textBox Text   defaultValue                                   break                                                                                    else                                       textBox Text   defaultValue                                     break                                    And here is some example of its easy usage    lt TextBox viewHelpers TextBoxHelper OnlyNumeric  Double           viewHelpers TextBoxHelper DefaultValue  1   gt    Or    lt TextBox viewHelpers TextBoxHelper OnlyNumeric  Natural           viewHelpers TextBoxHelper DefaultValue  3           viewHelpers TextBoxHelper EvenOddConstraint  OnlyOdd   gt    Note that my TextBoxHelper resides in the viewHelpers xmlns alias   I hope that this implementation eases some other one s work

User · Answer

e Handled    int e Key  gt   43     int e Key  lt   34    in preview keydown event of textbox

User · Answer

I used some of what was already here and put my own twist on it using a behavior so I don t have to propagate this code throughout a ton of Views     public class AllowableCharactersTextBoxBehavior   Behavior lt TextBox gt        public static readonly DependencyProperty RegularExpressionProperty            DependencyProperty Register  RegularExpression   typeof string   typeof AllowableCharactersTextBoxBehavior            new FrameworkPropertyMetadata             public string RegularExpression               get                       return  string base GetValue RegularExpressionProperty                     set                       base SetValue RegularExpressionProperty  value                        public static readonly DependencyProperty MaxLengthProperty           DependencyProperty Register  MaxLength   typeof int   typeof AllowableCharactersTextBoxBehavior           new FrameworkPropertyMetadata int MinValue        public int MaxLength               get                       return  int base GetValue MaxLengthProperty                     set                       base SetValue MaxLengthProperty  value                        protected override void OnAttached                 base OnAttached            AssociatedObject PreviewTextInput    OnPreviewTextInput          DataObject AddPastingHandler AssociatedObject  OnPaste              private void OnPaste object sender  DataObjectPastingEventArgs e                if  e DataObject GetDataPresent DataFormats Text                         string text   Convert ToString e DataObject GetData DataFormats Text                 if   IsValid text  true                                 e CancelCommand                                    else                       e CancelCommand                         void OnPreviewTextInput object sender  System Windows Input TextCompositionEventArgs e                e Handled    IsValid e Text  false              protected override void OnDetaching                 base OnDetaching            AssociatedObject PreviewTextInput -  OnPreviewTextInput          DataObject RemovePastingHandler AssociatedObject  OnPaste              private bool IsValid string newText  bool paste                return  ExceedsMaxLength newText  paste   amp  amp  Regex IsMatch newText  RegularExpression              private bool ExceedsMaxLength string newText  bool paste                if  MaxLength    0  return false           return LengthOfModifiedText newText  paste   gt  MaxLength             private int LengthOfModifiedText string newText  bool paste                var countOfSelectedChars   this AssociatedObject SelectedText Length          var caretIndex   this AssociatedObject CaretIndex          string text   this AssociatedObject Text           if  countOfSelectedChars  gt  0    paste                        text   text Remove caretIndex  countOfSelectedChars               return text Length   newText Length                    else                       var insert   Keyboard IsKeyToggled Key Insert                return insert  amp  amp  caretIndex  lt  text Length   text Length   text Length   newText Length                      Here is the relevant view code    lt TextBox MaxLength  50  TextWrapping  Wrap  MaxWidth  150  Margin  4   Text   Binding Path FileNameToPublish    gt        lt interactivity Interaction Behaviors gt            lt v AllowableCharactersTextBoxBehavior RegularExpression    0-9  -     MaxLength  50    gt        lt  interactivity Interaction Behaviors gt   lt  TextBox gt

User · Answer

Add a preview text input event  Like so   lt TextBox PreviewTextInput  PreviewTextInput    gt    Then inside that set the e Handled if the text isn t allowed  e Handled    IsTextAllowed e Text    I use a simple regex in IsTextAllowed method to see if I should allow what they ve typed  In my case I only want to allow numbers  dots and dashes   private static readonly Regex  regex   new Regex    0-9 -        regex that matches disallowed text private static bool IsTextAllowed string text        return   regex IsMatch text       If you want to prevent pasting of incorrect data hook up the DataObject Pasting event DataObject Pasting  TextBoxPasting  as shown here  code excerpted       Use the DataObject Pasting Handler  private void TextBoxPasting object sender  DataObjectPastingEventArgs e        if  e DataObject GetDataPresent typeof String                  String text    String e DataObject GetData typeof String            if   IsTextAllowed text                         e CancelCommand                        else               e CancelCommand

User · Answer

In the WPF application  you can handle this by handling TextChanged event   void arsDigitTextBox TextChanged object sender  System Windows Controls TextChangedEventArgs e        Regex regex   new Regex    0-9          bool handle   regex IsMatch this Text       if  handle                StringBuilder dd   new StringBuilder            int i   -1          int cursor   -1          foreach  char item in this Text                        i                if  char IsDigit item                   dd Append item               else if cursor    -1                  cursor   i                    this Text   dd ToString             if  i    -1              this SelectionStart   this Text Length          else             this SelectionStart   cursor

User · Answer

Here is my version of it  It s based on a base ValidatingTextBox class that just undoes what has been done if it s not  valid   It supports paste  cut  delete  backspace     - etc   For 32-bit integer  there is a Int32TextBox class that just compares with an int  I have also added floating point validation classes   public class ValidatingTextBox   TextBox       private bool  inEvents      private string  textBefore      private int  selectionStart      private int  selectionLength       public event EventHandler lt ValidateTextEventArgs gt  ValidateText       protected override void OnPreviewKeyDown KeyEventArgs e                if   inEvents              return            selectionStart   SelectionStart           selectionLength   SelectionLength           textBefore   Text             protected override void OnTextChanged TextChangedEventArgs e                if   inEvents              return            inEvents   true          var ev   new ValidateTextEventArgs Text           OnValidateText this  ev           if  ev Cancel                        Text    textBefore              SelectionStart    selectionStart              SelectionLength    selectionLength                     inEvents   false             protected virtual void OnValidateText object sender  ValidateTextEventArgs e    gt  ValidateText  Invoke this  e      public class ValidateTextEventArgs   CancelEventArgs       public ValidateTextEventArgs string text    gt  Text   text       public string Text   get       public class Int32TextBox   ValidatingTextBox       protected override void OnValidateText object sender  ValidateTextEventArgs e    gt  e Cancel    int TryParse e Text  out var value      public class Int64TextBox   ValidatingTextBox       protected override void OnValidateText object sender  ValidateTextEventArgs e    gt  e Cancel    long TryParse e Text  out var value      public class DoubleTextBox   ValidatingTextBox       protected override void OnValidateText object sender  ValidateTextEventArgs e    gt  e Cancel    double TryParse e Text  out var value      public class SingleTextBox   ValidatingTextBox       protected override void OnValidateText object sender  ValidateTextEventArgs e    gt  e Cancel    float TryParse e Text  out var value      public class DecimalTextBox   ValidatingTextBox       protected override void OnValidateText object sender  ValidateTextEventArgs e    gt  e Cancel    decimal TryParse e Text  out var value       Note 1  When using WPF binding  you must make sure you use the class that fits the bound property type otherwise  it may lead to strange results   Note 2  When using floating point classes with WPF binding  make sure the binding uses the current culture to match the TryParse method I ve used

User · Answer

PreviewTextInput     s  e    gt        e Handled    e Text All char IsDigit

User · Answer

The following code creates a control which you will be able to use like a normal TextBox however it will only take a positive double as an input  In the XAML you ll be able to use this control like so   lt local UnsignedDoubleBox  gt   In the C  code add the following inside the current namespace  public class UnsignedDoubleBox   TextBox               public UnsignedDoubleBox                         this PreviewTextInput    defaultPreviewTextInput              DataObject AddPastingHandler this  defaultTextBoxPasting                      private bool IsTextAllowed TextBox textBox  String text                          source  https   stackoverflow com questions 23397195 in-wpf-does-previewtextinput-always-give-a-single-character-only comment89374810 23406386             String newText   textBox Text Insert textBox CaretIndex  text               double res              return double TryParse newText  out res   amp  amp  res  gt   0                      source  https   stackoverflow com a 1268648 13093413         private void defaultTextBoxPasting object sender  DataObjectPastingEventArgs e                        if  e DataObject GetDataPresent typeof String                                  String text    String e DataObject GetData typeof String                     if   IsTextAllowed  TextBox sender  text                                         e CancelCommand                                                else                               e CancelCommand                                     private void defaultPreviewTextInput object sender  TextCompositionEventArgs e                         if  IsTextAllowed  TextBox sender  e Text                                 e Handled   false                            else                               e Handled   true

User · Answer

This is an improved solution of WilPs answer   My improvements are    Improved behaviour on Del and Backspace buttons Added EmptyValue property  if empty string is inappropriate Fixed some minor typos         lt summary gt          Regular expression for Textbox with properties                lt see cref  RegularExpression   gt                 lt see cref  MaxLength   gt                lt see cref  EmptyValue   gt        lt  summary gt  public class TextBoxInputRegExBehaviour   Behavior lt TextBox gt         region DependencyProperties     public static readonly DependencyProperty RegularExpressionProperty           DependencyProperty Register  RegularExpression   typeof string   typeof TextBoxInputRegExBehaviour   new FrameworkPropertyMetadata              public string RegularExpression               get   return  string GetValue RegularExpressionProperty             set   SetValue RegularExpressionProperty  value                public static readonly DependencyProperty MaxLengthProperty           DependencyProperty Register  MaxLength   typeof int   typeof TextBoxInputRegExBehaviour                                           new FrameworkPropertyMetadata int MinValue         public int MaxLength               get   return  int GetValue MaxLengthProperty             set   SetValue MaxLengthProperty  value                public static readonly DependencyProperty EmptyValueProperty           DependencyProperty Register  EmptyValue   typeof string   typeof TextBoxInputRegExBehaviour   null        public string EmptyValue               get   return  string GetValue EmptyValueProperty             set   SetValue EmptyValueProperty  value                endregion           lt summary gt              Attach our behaviour  Add event handlers          lt  summary gt      protected override void OnAttached                 base OnAttached             AssociatedObject PreviewTextInput    PreviewTextInputHandler          AssociatedObject PreviewKeyDown    PreviewKeyDownHandler          DataObject AddPastingHandler AssociatedObject  PastingHandler                   lt summary gt              Deattach our behaviour  remove event handlers          lt  summary gt      protected override void OnDetaching                 base OnDetaching             AssociatedObject PreviewTextInput -  PreviewTextInputHandler          AssociatedObject PreviewKeyDown -  PreviewKeyDownHandler          DataObject RemovePastingHandler AssociatedObject  PastingHandler               region Event handlers  PRIVATE  --------------------------------------      void PreviewTextInputHandler object sender  TextCompositionEventArgs e                string text          if  this AssociatedObject Text Length  lt  this AssociatedObject CaretIndex              text   this AssociatedObject Text          else                           Remaining text after removing selected text              string remainingTextAfterRemoveSelection               text   TreatSelectedText out remainingTextAfterRemoveSelection                    remainingTextAfterRemoveSelection Insert AssociatedObject SelectionStart  e Text                    AssociatedObject Text Insert this AssociatedObject CaretIndex  e Text                      e Handled    ValidateText text                   lt summary gt              PreviewKeyDown event handler          lt  summary gt      void PreviewKeyDownHandler object sender  KeyEventArgs e                if  string IsNullOrEmpty this EmptyValue               return           string text   null              Handle the Backspace key         if  e Key    Key Back                        if   this TreatSelectedText out text                                 if  AssociatedObject SelectionStart  gt  0                      text   this AssociatedObject Text Remove AssociatedObject SelectionStart - 1  1                                      Handle the Delete key         else if  e Key    Key Delete                           If text was selected  delete it             if   this TreatSelectedText out text   amp  amp  this AssociatedObject Text Length  gt  AssociatedObject SelectionStart                                   Otherwise delete next symbol                 text   this AssociatedObject Text Remove AssociatedObject SelectionStart  1                                    if  text    string Empty                        this AssociatedObject Text   this EmptyValue              if  e Key    Key Back                  AssociatedObject SelectionStart                e Handled   true                       private void PastingHandler object sender  DataObjectPastingEventArgs e                if  e DataObject GetDataPresent DataFormats Text                         string text   Convert ToString e DataObject GetData DataFormats Text                 if   ValidateText text                   e CancelCommand                      else             e CancelCommand               endregion Event handlers  PRIVATE  -----------------------------------       region Auxiliary methods  PRIVATE  -----------------------------------           lt summary gt              Validate certain text by our regular expression and text length conditions          lt  summary gt           lt param name  text  gt  Text for validation  lt  param gt           lt returns gt  True - valid  False - invalid  lt  returns gt      private bool ValidateText string text                return  new Regex this RegularExpression  RegexOptions IgnoreCase   IsMatch text   amp  amp   MaxLength    int MinValue    text Length  lt   MaxLength                   lt summary gt              Handle text selection          lt  summary gt           lt returns gt true if the character was successfully removed  otherwise  false   lt  returns gt      private bool TreatSelectedText out string text                text   null          if  AssociatedObject SelectionLength  lt   0               return false           var length   this AssociatedObject Text Length          if  AssociatedObject SelectionStart  gt   length              return true           if  AssociatedObject SelectionStart   AssociatedObject SelectionLength  gt   length              AssociatedObject SelectionLength   length - AssociatedObject SelectionStart           text   this AssociatedObject Text Remove AssociatedObject SelectionStart  AssociatedObject SelectionLength           return true             endregion Auxiliary methods  PRIVATE  --------------------------------     Usage is pretty straightforward    lt i Interaction Behaviors gt       lt behaviours TextBoxInputRegExBehaviour RegularExpression    d    MaxLength  9  EmptyValue  0    gt   lt  i Interaction Behaviors gt

User · Answer

Could also simply implement a validation rule and apply it to the TextBox      lt TextBox gt       lt TextBox Text gt         lt Binding Path  OnyDigitInput  Mode  TwoWay  UpdateSourceTrigger  PropertyChanged  gt           lt Binding ValidationRules gt             lt conv OnlyDigitsValidationRule   gt           lt  Binding ValidationRules gt         lt  Binding gt       lt  TextBox Text gt    With the implementation of the rule as follow  using the same Regex as proposed in other answers    public class OnlyDigitsValidationRule   ValidationRule       public override ValidationResult Validate object value  CultureInfo cultureInfo                var validationResult   new ValidationResult true  null            if value    null                        if   string IsNullOrEmpty value ToString                                   var regex   new Regex    0-9 -        regex that matches disallowed text                 var parsingOk    regex IsMatch value ToString                     if   parsingOk                                        validationResult   new ValidationResult false   Illegal Characters  Please Enter Numeric Value                                                       return validationResult

User · Answer

When checking a number value you can use the VisualBasic IsNumeric function

User · Answer

After using some of the solutions here for some time  I developed my own that works well for my MVVM setup  Note that it s not as dynamic as some of the other ones in a sense of still allowing users to enter erroneous characters  but it blocks them from pressing the button and thus doing anything  This goes well with my theme of graying out buttons when actions cannot be performed   I have a TextBox that a user must enter a number of document pages to be printed    lt TextBox Text   Binding NumberPagesToPrint  UpdateSourceTrigger PropertyChanged    gt       with this binding property   private string  numberPagesToPrint  public string NumberPagesToPrint       get   return  numberPagesToPrint        set               if   numberPagesToPrint    value                        return                      numberPagesToPrint   value          OnPropertyChanged  NumberPagesToPrint              I also have a button    lt Button Template   DynamicResource CustomButton Flat   Content  Set          Command   Binding SetNumberPagesCommand    gt       with this command binding   private RelayCommand  setNumberPagesCommand  public ICommand SetNumberPagesCommand       get               if   setNumberPagesCommand    null                        int num               setNumberPagesCommand   new RelayCommand param   gt  SetNumberOfPages                         gt  Int32 TryParse NumberPagesToPrint  out num                       return  setNumberPagesCommand            And then there s the method of SetNumberOfPages    but it s unimportant for this topic  It works well in my case because I don t have to add any code into the View s code-behind file and it allows me to control behavior using the Command property

User · Answer

This is the only code needed   void MyTextBox PreviewTextInput object sender  TextCompositionEventArgs e        e Handled   new Regex    0-9     IsMatch e Text       This only allows numbers to be inputted into the text box   To allow a decimal point or minus sign  you can change the regular expression to   0-9 -

User · Answer

Add in a VALIDATION RULE so that when the text changes  check to determine if the data is numeric  and if it is  allows processing to continue  and if it is not  prompts the user that only numeric data is accepted in that field   Read more in Validation in Windows Presentation Foundation

User · Answer

Here I have a simple solution inspired by Ray s answer  This should be sufficient to identify any form of number  This solution can also be easily modified if you want only positive numbers  integer values or values accurate to a maximum number of decimal places  etc   As suggested in Ray s answer  you need to first add a PreviewTextInput event   lt TextBox PreviewTextInput  quot TextBox OnPreviewTextInput quot   gt   Then put the following in the code behind  private void TextBox OnPreviewTextInput object sender  TextCompositionEventArgs e        var textBox   sender as TextBox         Use SelectionStart property to find the caret position         Insert the previewed text into the existing text in the textbox      var fullText   textBox Text Insert textBox SelectionStart  e Text        double val         If parsing is successful  set Handled to false     e Handled    double TryParse fullText  out val       To invalid whitespace  we can add NumberStyles  using System Globalization   private void TextBox OnPreviewTextInput object sender  TextCompositionEventArgs e        var textBox   sender as TextBox         Use SelectionStart property to find the caret position         Insert the previewed text into the existing text in the textbox      var fullText   textBox Text Insert textBox SelectionStart  e Text        double val         If parsing is successful  set Handled to false     e Handled    double TryParse fullText                                    NumberStyles AllowDecimalPoint   NumberStyles AllowLeadingSign                                    CultureInfo InvariantCulture                                   out val

User · Answer

In Windows Forms it was easy  you can add an event for KeyPress and everything works easily  However  in WPF that event isn t there  But there is a much easier way for it   The WPF TextBox has the TextChanged event which is general for everything  It includes pasting  typing and whatever that can come up to your mind   So you can do something like this   XAML    lt TextBox name  txtBox1      TextChanged  TextBox TextChanged   gt    CODE BEHIND   private void TextBox TextChanged object sender  TextChangedEventArgs e        string s   Regex Replace   TextBox sender  Text       d                TextBox sender  Text   s      This also accepts     if you don t want it  just remove it from the regex statement to be     d    Note  This event can be used on many TextBox es as it uses the sender object s Text  You only write the event once and can use it for multiple TextBox es

User · Answer

Here is a very simple and easy way to do this using MVVM   Bind your textBox with an integer property in the view model  and this will work like a gem     it will even show validation when a non-integer is entered in the textbox   XAML code    lt TextBox x Name  contactNoTxtBox   Text   Binding contactNo     gt    View model code   private long  contactNo  public long contactNo       get   return  contactNo        set               if  value     contactNo              return           contactNo   value          OnPropertyChanged

User · Answer

We can do validation on text box changed event  The following implementation prevents keypress input other than numeric and one decimal point   private void textBoxNumeric TextChanged object sender  TextChangedEventArgs e                    TextBox textBox   sender as TextBox                 Int32 selectionStart   textBox SelectionStart                 Int32 selectionLength   textBox SelectionLength                 String newText   String Empty                 int count   0                 foreach  Char c in textBox Text ToCharArray                                           if  Char IsDigit c     Char IsControl c      c         amp  amp  count    0                                                        newText    c                               if  c                                            count    1                                                        textBox Text   newText                textBox SelectionStart   selectionStart  lt   textBox Text Length   selectionStart          textBox Text Length

User · Answer

How about this  Works well for me  Hope I didn t miss any edge cases     MyTextBox PreviewTextInput     sender  args    gt        if   int TryParse args Text  out                   args Handled   true            DataObject AddPastingHandler MyTextBox   sender  args    gt        var isUnicodeText   args SourceDataObject GetDataPresent DataFormats UnicodeText  true       if   isUnicodeText                args CancelCommand               var data   args SourceDataObject GetData DataFormats UnicodeText  as string      if   int TryParse data  out                   args CancelCommand

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I modified Rays answer to handle the highlighted text prior to checking the regular expression  I also adjusted the regular expression to only allow for two decimal places  currency   private static readonly Regex  regex   new Regex   quot   0-9  d     d 0 2     quot    private static bool IsTextAllowed string text        return  regex IsMatch text      private bool IsAllowed TextBox tb  string text        bool isAllowed   true      if  tb    null                string currentText   tb Text          if   string IsNullOrEmpty tb SelectedText               currentText   currentText Remove tb CaretIndex  tb SelectedText Length           isAllowed   IsTextAllowed currentText Insert tb CaretIndex  text              return isAllowed     private void Txt PreviewCurrencyTextInput object sender  TextCompositionEventArgs e        e Handled    IsAllowed sender as TextBox  e Text                   private void TextBoxPasting object sender  DataObjectPastingEventArgs e        if  e DataObject GetDataPresent typeof String                  String text    String e DataObject GetData typeof String            if   IsAllowed sender as TextBox  text               e CancelCommand              else         e CancelCommand       And the xaml  lt TextBox Name  quot Txt Textbox quot  PreviewTextInput  quot Txt PreviewCurrencyTextInput quot   DataObject Pasting  quot TextBoxPasting quot    gt

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This is what I would use to get a WPF textbox that accept digits and the decimal point   class numericTextBox   TextBox       protected override void OnKeyDown KeyEventArgs e                bool b   false          switch  e Key                        case Key Back  b   true  break              case Key D0  b   true  break              case Key D1  b   true  break              case Key D2  b   true  break              case Key D3  b   true  break              case Key D4  b   true  break              case Key D5  b   true  break              case Key D6  b   true  break              case Key D7  b   true  break              case Key D8  b   true  break              case Key D9  b   true  break              case Key OemPeriod  b   true  break                    if  b    false                        e Handled   true                    base OnKeyDown e             Put the code in a new class file  add  using System Windows Controls  using System Windows Input    at the top of the file and build the solution  The numericTextBox control will then appear at the top of the toolbox

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If you do not want to write a lot of code to do a basic function  I don t know why people make long methods  you can just do this    Add namespace   using System Text RegularExpressions   In XAML  set a TextChanged property    lt TextBox x Name  txt1  TextChanged  txt1 TextChanged   gt   In WPF under txt1 TextChanged method  add Regex Replace   private void txt1 TextChanged object sender  TextChangedEventArgs e        txt1 Text   Regex Replace txt1 Text     0-9

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Now I know this question has an accepted answer  but personally  I find it a bit confusing and I believe it should be easier than that  So I ll try to demonstrate how I got it to work as best as I can   In Windows Forms  there s an event called KeyPress which is perfectly good for this kind of task  But that doesn t exist in WPF  so instead  we ll be using the PreviewTextInput event  Also  for the validation  I believe one can use a foreach to loop through the textbox Text and check if it matches    the condition  but honestly  this is what regular expressions are for   One more thing before we dive into the holy code  For the event to be fired  one can do two things    Use XAML to tell the program which function to call   lt PreviewTextInput  textBox PreviewTextInput  gt  Do it in the Loaded event of the form  which the textBox is in   textBox PreviewTextInput    onlyNumeric    I think the second method is better because in situations like this  you ll mostly be required to apply the same condition  regex  to more than one TextBox and you don t want to repeat yourself    Finally  here s how you d do it   private void onlyNumeric object sender  TextCompositionEventArgs e        string onlyNumeric        0-9     0-9             Regex regex   new Regex onlyNumeric       e Handled    regex IsMatch e Text

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Here is a library for numeric input in WPF  It has properties like NumberStyles and RegexPatternfor validation   Subclasses WPF TextBox

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The event handler is previewing text input  Here a regular expression matches the text input only if it is not a number  and then it is not made to entry textbox   If you want only letters then replace the regular expression as   a-zA-Z    XAML   lt TextBox Name  NumberTextBox  PreviewTextInput  NumberValidationTextBox   gt    XAML CS FILE  using System Text RegularExpressions  private void NumberValidationTextBox object sender  TextCompositionEventArgs e        Regex regex   new Regex    0-9          e Handled   regex IsMatch e Text

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I allowed numeric keypad numbers and backspace       private void TextBox PreviewKeyDown object sender  KeyEventArgs e                int key    int e Key           e Handled     key  gt   34  amp  amp  key  lt   43                           key  gt   74  amp  amp  key  lt   83                           key    2

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I will assume that    Your TextBox for which you want to allow numeric input only has its Text property initially set to some valid number value  for example  2 7172   Your Textbox is a child of your main window Your main window is of class Window1 Your TextBox name is numericTB   Basic idea    Add  private string previousText  to your main window class  Window1  Add  previousText   numericTB Text  to your main window constructor Create a handler for the numericTB TextChanged event to be something like this   private void numericTB TextChanged object sender  TextChangedEventArgs e        double num   0      bool success   double TryParse   TextBox sender  Text  out num       if  success  amp  num  gt   0          previousText     TextBox sender  Text      else           TextBox sender  Text   previousText       This will keep setting previousText to numericTB Text as long as it is valid  and set numericTB Text to its last valid value if the user writes something that you don t like  Of course  this is just basic idea  and it is just  idiot resistant   not  idiot proof   It doesn t handle the case in which the user messes with spaces  for example  So here is a complete solution which I think is  idiot proof   and if I m wrong please tell me    Content of your Window1 xaml file    lt Window x Class  IdiotProofNumericTextBox Window1      xmlns  http   schemas microsoft com winfx 2006 xaml presentation      xmlns x  http   schemas microsoft com winfx 2006 xaml      Title  Window1  Height  300  Width  300  gt       lt Grid gt           lt TextBox Height  30  Width  100  Name  numericTB  TextChanged  numericTB TextChanged   gt       lt  Grid gt   lt  Window gt   Content of your Window xaml cs file   using System  using System Collections Generic  using System Linq  using System Text  using System Windows  using System Windows Controls  using System Windows Data  using System Windows Documents  using System Windows Input  using System Windows Media  using System Windows Media Imaging  using System Windows Navigation  using System Windows Shapes   namespace IdiotProofNumericTextBox       public partial class Window1   Window               private string previousText           public Window1                         InitializeComponent                previousText   numericTB Text                     private void numericTB TextChanged object sender  TextChangedEventArgs e                        if  string IsNullOrEmpty   TextBox sender  Text                   previousText                   else                               double num   0                  bool success   double TryParse   TextBox sender  Text  out num                   if  success  amp  num  gt   0                                          TextBox sender  Text Trim                        previousText     TextBox sender  Text                                    else                                         TextBox sender  Text   previousText                        TextBox sender  SelectionStart     TextBox sender  Text Length                                                       And that s it  If you have many TextBoxes then I recommend creating a CustomControl that inherits from TextBox  so you can wrap previousText and numericTB TextChanged up in a separate file

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The Extented WPF Toolkit has one  NumericUpDown

[c#] How do I get a TextBox to only accept numeric input in WPF?

For developers who want their text fields to accept unsigned numbers only such as socket ports and so on:

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