Validating a Textbox field for only numeric input

Question

I have created a form-based program that needs some input validation   I need to make sure the user can only enter numeric values within the distance Textbox   So far  I ve checked that the Textbox has something in it  but if it has a value then it should proceed to validate that the entered value is numeric   else if  txtEvDistance Text Length    0                        MessageBox Show  Please enter the distance              else if  cboAddEvent Text   is numeric                        MessageBox Show  Please enter a valid numeric distance

User · Answer

You can do it by javascript on client side or using some regex validator on the textbox   Javascript  script type  text javascript  language  javascript  gt      function validateNumbersOnly e            var unicode   e charCode   e charCode   e keyCode          if   unicode    8      unicode    9      unicode  gt  47  amp  amp  unicode  lt  58                 return true                    else                window alert  This field accepts only Numbers                return false                   lt  script gt    Textbox  with fixed ValidationExpression    lt asp TextBox ID  TextBox1  runat  server  gt  lt  asp TextBox gt   lt asp RegularExpressionValidator ID  RegularExpressionValidator6  runat  server  Display  None  ErrorMessage  Accepts only numbers   ControlToValidate  TextBox1  ValidationExpression    0-9     Text     gt  lt  asp RegularExpressionValidator gt

User · Answer

I have this extension which is kind of multi-purpose       public static bool IsNumeric this object value                if  value    null    value is DateTime                        return false                     if  value is Int16    value is Int32    value is Int64    value is Decimal    value is Single    value is Double    value is Boolean                        return true                     try                       if  value is string                  Double Parse value as string               else                 Double Parse value ToString                 return true                    catch             return false          It works for other data types  Should work fine for what you want to do

User · Answer

You can do this way        Check if the point entered is numeric or not    if  Int32 TryParse txtEvDistance Text  out var outParse                   Do what you want to do if numeric          else                 Do what you want to do if not numeric

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You may try the TryParse method which allows you to parse a string into an integer and return a boolean result indicating the success or failure of the operation   int distance  if  int TryParse txtEvDistance Text  out distance            it s a valid integer   gt  you could use the distance variable here

User · Answer

I agree with Int TryParse but as an alternative you could use Regex    Regex nonNumericRegex   new Regex    D     if  nonNumericRegex IsMatch txtEvDistance Text           Contains non numeric characters     return false

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If you want to prevent the user from enter non-numeric values at the time of enter the information in the TextBox  you can use the Event OnKeyPress like this   private void txtAditionalBatch KeyPress object sender  KeyPressEventArgs e                        if   char IsDigit e KeyChar   e Handled   true            Just Digits             if  e KeyChar     char 8  e Handled   false               Allow Backspace             if  e KeyChar     char 13  btnSearch Click sender  e      Allow Enter                         This solution doesn t work if the user paste the information in the TextBox using the mouse  right click   paste  in that case you should add an extra validation

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I know this is an old question but I figured out I should pitch my answer anyways  The following snippet iterates through each character of the text and uses the IsNumber   method  which returns true if the character is a number and false the other way  to check if all the characters are numbers  If all are numbers  the method returns true  If not it returns false  using System   private bool ValidateText string text       char   characters   text ToCharArray         foreach char c in characters           if  char IsNumber c               return false            return true

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if  int TryParse txtDepartmentNo Text  out checkNumber     false                        lblMessage Text   string Empty              lblMessage Visible   true              lblMessage ForeColor   Color Maroon              lblMessage Text    You have not entered a number               return

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Here s a solution that allows either numeric only with a minus sign or decimal with a minus sign and decimal point   Most of the previous answers did not take into account selected text   If you change your textbox s ShortcutsEnabled to false  then you can t paste garbage into your textbox either  it disables right-clicking    Some solutions allowed you to enter data before the minus   Please verify that I ve caught everything           private bool DecimalOnly KeyPress TextBox txt  bool numeric  KeyPressEventArgs e                        if  numeric                                   Test first character - either text is blank or the selection starts at first character                  if  txt Text          txt SelectionStart    0                                           If the first character is a minus or digit  AND                        if the text does not contain a minus OR the selected text DOES contain a minus                      if   e KeyChar     -     char IsDigit e KeyChar    amp  amp    txt Text Contains  -      txt SelectedText Contains  -                             return false                      else                         return true                                    else                                          If it s not the first character  then it must be a digit or backspace                     if  char IsDigit e KeyChar     e KeyChar    Convert ToChar Keys Back                           return false                      else                         return true                                              else                                  Test first character - either text is blank or the selection starts at first character                  if  txt Text          txt SelectionStart    0                                           If the first character is a minus or digit  AND                        if the text does not contain a minus OR the selected text DOES contain a minus                      if   e KeyChar     -     char IsDigit e KeyChar    amp  amp    txt Text Contains  -      txt SelectedText Contains  -                             return false                      else                                                  If the first character is a decimal point or digit  AND                            if the text does not contain a decimal point OR the selected text DOES contain a decimal point                          if   e KeyChar           char IsDigit e KeyChar    amp  amp    txt Text Contains         txt SelectedText Contains                                    return false                          else                             return true                                                          else                                          If it s not the first character  then it must be a digit or backspace OR                        a decimal point AND                        if the text does not contain a decimal point or the selected text does contain a decimal point                      if  char IsDigit e KeyChar     e KeyChar    Convert ToChar Keys Back      e KeyChar         amp  amp    txt Text Contains         txt SelectedText Contains                                 return false                      else                         return true

User · Answer

Use Regex as below  if  txtNumeric Text Length  lt  0     System Text RegularExpressions Regex IsMatch txtNumeric Text   quot   0-9    quot       MessageBox show  quot add content quot      else    MessageBox show  quot add content quot

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Here is another simple solution   try       int temp Convert ToInt32 txtEvDistance Text     catch Exception h        MessageBox Show  Please provide number only

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To check if the value is a double   private void button1 Click object sender  EventArgs e         if   double TryParse textBox1 Text  out var x                 System Console WriteLine  it s not a double             return            System Console WriteLine  it s a double

[c#] Validating a Textbox field for only numeric input.

Javascript

Textbox (with fixed ValidationExpression)

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