How to bind to a PasswordBox in MVVM

Question

I have come across a problem with binding to a PasswordBox  It seems it s a security risk but I am using the MVVM pattern so I wish to bypass this  I found some interesting code here  has anyone used this or something similar   http   www wpftutorial net PasswordBox html It technically looks great  but I am unsure of how to retrieve the password  I basically have properties in my LoginViewModel for Username and Password  Username is fine and is working as it s a TextBox  I used the code above as stated and entered this  lt PasswordBox ff PasswordHelper Attach  quot True quot      ff PasswordHelper Password  quot  Binding Path Password  quot  Width  quot 130 quot   gt   When I had the PasswordBox as a TextBox and Binding Path Password then the property in my LoginViewModel was updated  My code is very simple  basically I have a Command for my Button  When I press it CanLogin is called and if it returns true it calls Login  You can see I check my property for Username here which works great  In Login I send along to my service a Username and Password  Username contains data from my View but Password is Null Empty private DelegateCommand loginCommand   public string Username   get  set    public string Password   get  set      public ICommand LoginCommand       get               if  loginCommand    null                        loginCommand   new DelegateCommand                  Login  CanLogin                      return loginCommand           private bool CanLogin         return  string IsNullOrEmpty Username      private void Login         bool result   securityService IsValidLogin Username  Password        if  result          else         This is what I am doing  lt TextBox Text  quot  Binding Path Username  UpdateSourceTrigger PropertyChanged  quot           MinWidth  quot 180 quot    gt    lt PasswordBox ff PasswordHelper Attach  quot True quot                ff PasswordHelper Password  quot  Binding Path Password  quot  Width  quot 130 quot   gt   I have my TextBox  this is no problem  but in my ViewModel the Password is empty  Am I doing something wrong or missing a step  I put a breakpoint and sure enough the code enter the static helper class but it never updates my Password in my ViewModel

User · Answer

For complete newbies like me  here is a complete working sample of what Konamiman suggested above  Thanks Konamiman  XAML      lt PasswordBox x Name  quot textBoxPassword quot   gt       lt Button x Name  quot buttonLogin quot  Content  quot Login quot              Command  quot  Binding PasswordCommand  quot              CommandParameter  quot  Binding ElementName textBoxPassword  quot   gt    ViewModel public class YourViewModel   ViewModelBase       private ICommand  passwordCommand      public ICommand PasswordCommand               get               if   passwordCommand    null                     passwordCommand   new RelayCommand lt object gt  PasswordClick                             return  passwordCommand                       public YourViewModel                    private void PasswordClick object p                var password   p as PasswordBox          Console WriteLine  quot Password is   0  quot   password Password

User · Answer

I spent a great deal of time looking at various solutions  I didn t like the decorators idea  behaviors mess up the validation UI  code behind    really    The best one yet is to stick to a custom attached property and bind to your SecureString property in your view model  Keep it in there for as long as you can  Whenever you ll need quick access to the plain password  temporarily convert it to an unsecure string using the code below   namespace Namespace Extensions       using System      using System Runtime InteropServices      using System Security            lt summary gt          Provides unsafe temporary operations on secured strings           lt  summary gt       SuppressUnmanagedCodeSecurity      public static class SecureStringExtensions                    lt summary gt              Converts a secured string to an unsecured string               lt  summary gt          public static string ToUnsecuredString this SecureString secureString                           copy amp paste from the internal System Net UnsafeNclNativeMethods             IntPtr bstrPtr   IntPtr Zero              if  secureString    null                                if  secureString Length    0                                        try                                               bstrPtr   Marshal SecureStringToBSTR secureString                           return Marshal PtrToStringBSTR bstrPtr                                             finally                                               if  bstrPtr    IntPtr Zero                              Marshal ZeroFreeBSTR bstrPtr                                                                     return string Empty                          lt summary gt              Copies the existing instance of a secure string into the destination  clearing the destination beforehand               lt  summary gt          public static void CopyInto this SecureString source  SecureString destination                        destination Clear                foreach  var chr in source ToUnsecuredString                                  destination AppendChar chr                                         lt summary gt              Converts an unsecured string to a secured string               lt  summary gt          public static SecureString ToSecuredString this string plainString                        if  string IsNullOrEmpty plainString                                 return new SecureString                               SecureString secure   new SecureString                foreach  char c in plainString                                secure AppendChar c                             return secure                      Make sure you allow the GC to collect your UI element  so resist the urge of using a static event handler for the PasswordChanged event on the PasswordBox   I also discovered an anomaly where the control wasn t updating the UI when using the SecurePassword property for setting it up  reason why I m copying the password into Password instead    namespace Namespace Controls       using System Security      using System Windows      using System Windows Controls      using Namespace Extensions            lt summary gt          Creates a bindable attached property for the  lt see cref  PasswordBox SecurePassword   gt  property           lt  summary gt      public static class PasswordBoxHelper                  an attached behavior won t work due to view model validation not picking up the right control to adorn         public static readonly DependencyProperty SecurePasswordBindingProperty   DependencyProperty RegisterAttached               SecurePassword               typeof SecureString               typeof PasswordBoxHelper               new FrameworkPropertyMetadata new SecureString   FrameworkPropertyMetadataOptions BindsTwoWayByDefault  AttachedPropertyValueChanged                      private static readonly DependencyProperty  passwordBindingMarshallerProperty   DependencyProperty RegisterAttached               PasswordBindingMarshaller               typeof PasswordBindingMarshaller               typeof PasswordBoxHelper               new PropertyMetadata                       public static void SetSecurePassword PasswordBox element  SecureString secureString                        element SetValue SecurePasswordBindingProperty  secureString                      public static SecureString GetSecurePassword PasswordBox element                        return element GetValue SecurePasswordBindingProperty  as SecureString                     private static void AttachedPropertyValueChanged DependencyObject d  DependencyPropertyChangedEventArgs e                           we ll need to hook up to one of the element s events                in order to allow the GC to collect the control  we ll wrap the event handler inside an object living in an attached property                don t be tempted to use the Unloaded event as that will be fired  even when the control is still alive and well  e g  switching tabs in a tab control               var passwordBox    PasswordBox d              var bindingMarshaller   passwordBox GetValue  passwordBindingMarshallerProperty  as PasswordBindingMarshaller              if  bindingMarshaller    null                                bindingMarshaller   new PasswordBindingMarshaller passwordBox                   passwordBox SetValue  passwordBindingMarshallerProperty  bindingMarshaller                              bindingMarshaller UpdatePasswordBox e NewValue as SecureString                           lt summary gt              Encapsulated event logic              lt  summary gt          private class PasswordBindingMarshaller                       private readonly PasswordBox  passwordBox              private bool  isMarshalling               public PasswordBindingMarshaller PasswordBox passwordBox                                 passwordBox   passwordBox                   passwordBox PasswordChanged    this PasswordBoxPasswordChanged                             public void UpdatePasswordBox SecureString newPassword                                if   isMarshalling                                        return                                      isMarshalling   true                  try                                          setting up the SecuredPassword won t trigger a visual update so we ll have to use the Password property                      passwordBox Password   newPassword ToUnsecuredString                            you may try the statement below  however the benefits are minimal security wise  you still have to extract the unsecured password for copying                        newPassword CopyInto  passwordBox SecurePassword                                     finally                                        isMarshalling   false                                               private void PasswordBoxPasswordChanged object sender  RoutedEventArgs e                                   copy the password into the attached property                 if   isMarshalling                                        return                                      isMarshalling   true                  try                                       SetSecurePassword  passwordBox   passwordBox SecurePassword Copy                                       finally                                        isMarshalling   false                                                      And the XAML usage    lt PasswordBox controls PasswordBoxHelper SecurePassword   Binding LogonPassword  UpdateSourceTrigger PropertyChanged  ValidatesOnDataErrors True   gt    My property in the view model looked like this    RequiredSecureString  public SecureString LogonPassword      get             return  logonPassword          set              logonPassword   value         NotifyPropertyChanged nameof LogonPassword             The RequiredSecureString is just a simple custom validator that has the following logic    AttributeUsage AttributeTargets Property   AttributeTargets Field  AllowMultiple   true       public class RequiredSecureStringAttribute ValidationAttribute       public RequiredSecureStringAttribute            base  Field is required                                public override bool IsValid object value                return  value as SecureString   Length  gt  0            Here you have it  A complete and tested pure MVVM solution

User · Answer

My 2 cents   I developed once a typical login dialog  user and password boxes  plus  Ok  button  using WPF and MVVM  I solved the password binding issue by simply passing the PasswordBox control itself as a parameter to the command attached to the  Ok  button  So in the view I had    lt PasswordBox Name  txtPassword  VerticalAlignment  Top  Width  120    gt   lt Button Content  Ok  Command   Binding Path OkCommand      CommandParameter   Binding ElementName txtPassword    gt    And in the ViewModel  the Execute method of the attached command was as follows   void Execute object parameter        var passwordBox   parameter as PasswordBox      var password   passwordBox Password        Now go ahead and check the user name and password     This slightly violates the MVVM pattern since now the ViewModel knows something about how the View is implemented  but in that particular project I could afford it  Hope it is useful for someone as well

User · Answer

I used this method and passed the password box  although this does violate the MVVM it was essential for me because I was using a content control with data template for my login within my shell which is a complex shell enviroment  So accessing the code behind of the shell would have been crap   Passing the passwordbox I would think is same as accessing control from code behind as far as I know  I agree passwords  dont keep in memory etc In this implementation I don t have property for password in view model   Button Command  Command   Binding Path DataContext LoginCommand  ElementName MyShell   CommandParameter   Binding ElementName PasswordBox     ViewModel  private void Login object parameter        System Windows Controls PasswordBox p    System Windows Controls PasswordBox parameter      MessageBox Show p Password

User · Answer

I am using succinct MVVM-friendly solution that hasn t been mentioned yet  First  I name the PasswordBox in XAML    lt PasswordBox x Name  Password    gt    Then I add a single method call into view constructor   public LoginWindow         InitializeComponent        ExposeControl lt LoginViewModel gt  Expose this  view   gt  view Password           model  box    gt  model SetPasswordBox box        And that s it  View model will receive notification when it is attached to a view via DataContext and another notification when it is detached  The contents of this notification are configurable via the lambdas  but usually it s just a setter or method call on the view model  passing the problematic control as a parameter   It can be made MVVM-friendly very easily by having the view expose interface instead of child controls   The above code relies on helper class published on my blog

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As you can see i am binding to Password  but maybe its bind it to the static class     It is an attached property  This kind of property can be applied to any kind of DependencyObject  not just the type in which it is declared  So even though it is declared in the PasswordHelper static class  it is applied to the PasswordBox on which you use it   To use this attached property  you just need to bind it to the Password property in your ViewModel     lt PasswordBox w PasswordHelper Attach  True            w PasswordHelper Password   Binding Password    gt

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I spent ages trying to get this working  In the end  I gave up and just used the PasswordBoxEdit from DevExpress   It is the simplest solution ever  as it allows binding without pulling any horrible tricks   Solution on DevExpress website  For the record  I am not affiliated with DevExpress in any way

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I posted a GIST here that is a bindable password box   using System Windows  using System Windows Controls   namespace CustomControl       public class BindablePasswordBox   Decorator                    lt summary gt              The password dependency property               lt  summary gt          public static readonly DependencyProperty PasswordProperty           private bool isPreventCallback          private RoutedEventHandler savedCallback                lt summary gt              Static constructor to initialize the dependency properties               lt  summary gt          static BindablePasswordBox                         PasswordProperty   DependencyProperty Register                   Password                   typeof string                   typeof BindablePasswordBox                   new FrameworkPropertyMetadata     FrameworkPropertyMetadataOptions BindsTwoWayByDefault  new PropertyChangedCallback OnPasswordPropertyChanged                                          lt summary gt              Saves the password changed callback and sets the child element to the password box               lt  summary gt          public BindablePasswordBox                         savedCallback   HandlePasswordChanged               PasswordBox passwordBox   new PasswordBox                passwordBox PasswordChanged    savedCallback              Child   passwordBox                          lt summary gt              The password dependency property               lt  summary gt          public string Password                       get   return GetValue PasswordProperty  as string                set   SetValue PasswordProperty  value                             lt summary gt              Handles changes to the password dependency property               lt  summary gt               lt param name  d  gt the dependency object lt  param gt               lt param name  eventArgs  gt the event args lt  param gt          private static void OnPasswordPropertyChanged DependencyObject d  DependencyPropertyChangedEventArgs eventArgs                        BindablePasswordBox bindablePasswordBox    BindablePasswordBox  d              PasswordBox passwordBox    PasswordBox  bindablePasswordBox Child               if  bindablePasswordBox isPreventCallback                                return                             passwordBox PasswordChanged -  bindablePasswordBox savedCallback              passwordBox Password    eventArgs NewValue    null    eventArgs NewValue ToString                     passwordBox PasswordChanged    bindablePasswordBox savedCallback                          lt summary gt              Handles the password changed event               lt  summary gt               lt param name  sender  gt the sender lt  param gt               lt param name  eventArgs  gt the event args lt  param gt          private void HandlePasswordChanged object sender  RoutedEventArgs eventArgs                        PasswordBox passwordBox    PasswordBox  sender               isPreventCallback   true              Password   passwordBox Password              isPreventCallback   false

User · Answer

x000D   x000D   lt UserControl x Class  Elections Server Handler Views LoginView  x000D               xmlns  http   schemas microsoft com winfx 2006 xaml presentation  x000D               xmlns x  http   schemas microsoft com winfx 2006 xaml  x000D               xmlns mc  http   schemas openxmlformats org markup-compatibility 2006   x000D               xmlns d  http   schemas microsoft com expression blend 2008  x000D               xmlns i  clr-namespace System Windows Interactivity assembly System Windows Interactivity  x000D               xmlns cal  http   www caliburnproject org  x000D               mc Ignorable  d   x000D               Height  531  Width  1096  gt  x000D       lt ContentControl gt  x000D           lt ContentControl Background gt  x000D               lt ImageBrush  gt  x000D           lt  ContentControl Background gt  x000D           lt Grid  gt  x000D               lt Border BorderBrush   FFABADB3  BorderThickness  1  HorizontalAlignment  Left  Height  23  Margin  900 100 0 0  VerticalAlignment  Top  Width  160  gt  x000D                   lt TextBox TextWrapping  Wrap   gt  x000D               lt  Border gt  x000D               lt Border BorderBrush   FFABADB3  BorderThickness  1  HorizontalAlignment  Left  Height  23  Margin  900 150 0 0  VerticalAlignment  Top  Width  160  gt  x000D                   lt PasswordBox x Name  PasswordBox   gt  x000D               lt  Border gt  x000D               lt Button Content  Login  HorizontalAlignment  Left  Margin  985 200 0 0  VerticalAlignment  Top  Width  75  gt  x000D                   lt i Interaction Triggers gt  x000D                       lt i EventTrigger EventName  Click  gt  x000D                           lt cal ActionMessage MethodName  Login  gt  x000D                               lt cal Parameter Value   Binding ElementName PasswordBox     gt  x000D                           lt  cal ActionMessage gt  x000D                       lt  i EventTrigger gt  x000D                   lt  i Interaction Triggers gt  x000D               lt  Button gt  x000D   x000D           lt  Grid gt  x000D       lt  ContentControl gt  x000D   lt  UserControl gt  x000D   x000D   x000D     x000D   x000D  using System  x000D  using System Windows  x000D  using System Windows Controls  x000D  using Caliburn Micro  x000D   x000D  namespace Elections Server Handler ViewModels x000D    x000D      public class LoginViewModel   PropertyChangedBase x000D        x000D          MainViewModel  mainViewModel  x000D          public void SetMain MainViewModel mainViewModel  x000D            x000D               mainViewModel   mainViewModel  x000D            x000D   x000D          public void Login Object password  x000D            x000D              var pass    PasswordBox  password  x000D              MessageBox Show pass Password   x000D   x000D                 mainViewModel ScreenView    mainViewModel ControlPanelView  x000D                 mainViewModel TitleWindow    Panel de Control   x000D                HandlerBootstrapper Title  mainViewModel TitleWindow   x000D            x000D        x000D    x000D   x000D   x000D       easy

User · Answer

Its very simple   Create another property for password and Bind this with TextBox  But all input operations perform with actual password property  private string  Password       public string PasswordChar               get                       string szChar                    foreach char szCahr in  Password                                szChar   szChar                                   return szChar                     set                        PasswordChar   value  NotifyPropertyChanged                      public string Password                       get                               return  Password                         set                        Password   value  NotifyPropertyChanged                PasswordChar    Password

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This works just fine for me    lt Button Command   Binding Connect            CommandParameter   Binding ElementName MyPasswordBox    gt

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To me  both of these things feel wrong    Implementing clear text password properties Sending the PasswordBox as a command parameter to the ViewModel   Transferring the SecurePassword  SecureString instance  as described by Steve in CO seems acceptable  I prefer Behaviors to code behind  and I also had the additional requirement of being able to reset the password from the viewmodel   Xaml  Password is the ViewModel property     lt PasswordBox gt       lt i Interaction Behaviors gt           lt behaviors PasswordBinding BoundPassword   Binding Password  Mode TwoWay     gt       lt  i Interaction Behaviors gt   lt  PasswordBox gt    Behavior   using System Security  using System Windows  using System Windows Controls  using System Windows Interactivity   namespace Evidence OutlookIntegration AddinLogic Behaviors            lt summary gt          Intermediate class that handles password box binding  which is not possible directly            lt  summary gt      public class PasswordBoxBindingBehavior   Behavior lt PasswordBox gt                   BoundPassword         public SecureString BoundPassword   get   return  SecureString GetValue BoundPasswordProperty     set   SetValue BoundPasswordProperty  value               public static readonly DependencyProperty BoundPasswordProperty   DependencyProperty Register  BoundPassword   typeof SecureString   typeof PasswordBoxBindingBehavior   new FrameworkPropertyMetadata OnBoundPasswordChanged             protected override void OnAttached                         this AssociatedObject PasswordChanged    AssociatedObjectOnPasswordChanged              base OnAttached                            lt summary gt              Link up the intermediate SecureString  BoundPassword  to the UI instance              lt  summary gt          private void AssociatedObjectOnPasswordChanged object s  RoutedEventArgs e                        this BoundPassword   this AssociatedObject SecurePassword                          lt summary gt              Reacts to password reset on viewmodel  ViewModel Password   new SecureString                 lt  summary gt          private static void OnBoundPasswordChanged object s  DependencyPropertyChangedEventArgs e                        var box     PasswordBoxBindingBehavior s  AssociatedObject              if  box    null                                if    SecureString e NewValue  Length    0                      box Password   string Empty

User · Answer

While I agree it s important to avoid storing the password anywhere  I still need the ability to instantiate the view model without a view and execute my tests against it   The solution that worked for me was to register the PasswordBox Password function with the view model  and have the view model invoke it when executing the login code   This does mean a line of code in the view s codebehind   So  in my Login xaml I have   lt PasswordBox x Name  PasswordBox   gt    and in Login xaml cs I have  LoginViewModel PasswordHandler        gt  PasswordBox Password    then in LoginViewModel cs I have the PasswordHandler defined  public Func lt string gt  PasswordHandler   get  set      and when login needs to happen the code invokes the handler to get the password from the view     bool loginResult   Login Username  PasswordHandler       This way  when I want to test the viewmodel I can simply set PasswordHandler to an anonymous method that lets me deliver whatever password I want to use in the test

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Maybe I am missing something  but it seems like most of these solutions overcomplicate things and do away with secure practices    This method does not violate the MVVM pattern and maintains complete security  Yes  technically it is code behind  but it is nothing more than a  special case  binding  The ViewModel still has no knowledge of the View implementation  which in my mind it does if you are trying to pass the PasswordBox in to the ViewModel    Code Behind    Automatic MVVM violation  It all depends on what you do with it  In this case  we are just manually coding a binding  so its all considered part of the UI implementation and therefore is ok   In the ViewModel  just a simple property  I made it  write only  since there shouldn t be a need to retrieve it from outside the ViewModel for any reason  but it doesn t have to be  Note that it is a SecureString  not just a string   public SecureString SecurePassword   private get  set      In the xaml  you set up a PasswordChanged event handler    lt PasswordBox PasswordChanged  PasswordBox PasswordChanged   gt    In the code behind   private void PasswordBox PasswordChanged object sender  RoutedEventArgs e        if  this DataContext    null          dynamic this DataContext  SecurePassword     PasswordBox sender  SecurePassword        With this method  your password remains in a SecureString at all times and therefore provides maximum security  If you really don t care about security or you need the clear text password for a downstream method that requires it  note  most  NET methods that require a password also support a SecureString option  so you may not really need a clear text password even if you think you do   you can just use the Password property instead  Like this    ViewModel property   public string Password   private get  set       Code behind   private void PasswordBox PasswordChanged object sender  RoutedEventArgs e        if  this DataContext    null          dynamic this DataContext  Password     PasswordBox sender  Password        If you wanted to keep things strongly typed  you could substitute the  dynamic  cast with the interface of your ViewModel  But really   normal  data bindings aren t strongly typed either  so its not that big a deal   private void PasswordBox PasswordChanged object sender  RoutedEventArgs e        if  this DataContext    null          IMyViewModel this DataContext  Password     PasswordBox sender  Password        So best of all worlds - your password is secure  your ViewModel just has a property like any other property  and your View is self contained with no external references required

User · Answer

Here s my take on it     Using an attached property to bind the password defeats the purpose of securing the password  The Password property of a password box is not bindable for a reason  Passing the password box as command parameter will make the ViewModel aware of the control  This will not work if you plan to make your ViewModel reusable cross platform  Don t make your VM aware of your View or any other controls  I don t think introducing a new property  an interface  subscribing to password changed events or any other complicated things is necessary for a simple task of providing the password     XAML   lt PasswordBox x Name  pbPassword    gt   lt Button Content  Login  Command   Binding LoginCommand   x Name  btnLogin   gt    Code behind - using code behind does not necessarily violate MVVM  As long as you don t put any business logic in it   btnLogin CommandParameter   new Func lt string gt      gt pbPassword Password      ViewModel  LoginCommand   new RelayCommand lt Func lt string gt  gt  getpwd  gt    service Login username  getpwd

User · Answer

For anyone who is aware of the risks this implementation imposes  to have the password sync to your ViewModel simply add Mode OneWayToSource   XAML   lt PasswordBox     ff PasswordHelper Attach  True      ff PasswordHelper Password   Binding Path Password  Mode OneWayToSource     gt

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In windows universal app  you can use this code with the property  Password  and binding with the modelView   x000D   x000D    lt PasswordBox x Uid  PasswordBox  Password   Binding Waiter Password  Mode TwoWay   Name  txtPassword  HorizontalAlignment  Stretch  Margin  50 200 50 0  VerticalAlignment  Top   gt  x000D   x000D   x000D

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I used an authentication check followed by a sub called by a mediator class to the View  which also implements an authentication check  to write the password to the data class   It s not a perfect solution  however  it remedied my problem of not being able to move the password

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I have done like   XAML    lt PasswordBox x Name  NewPassword  PasswordChanged  NewPassword PasswordChanged   gt   lt  --change tablenameViewSource  yours -- gt   lt Grid DataContext   StaticResource tablenameViewSource   Visibility  Hidden  gt           lt TextBox x Name  Password  Text   Binding password  Mode TwoWay    gt   lt  Grid gt    C    private void NewPassword PasswordChanged object sender  RoutedEventArgs e                try                        change tablenameDataTable  yours  and tablenameViewSource  yours             tablenameDataTable Rows tablenameViewSource View CurrentPosition   password     NewPassword Password                    catch                       this Password Text   this NewPassword Password                    It works for me

User · Answer

As mentioned before VM should be unaware of the View but passing whole PasswordBox looks like the simplest approach  So maybe instead of casting passed parameter to PasswordBox use Reflection to extract Password property from it  In this case VM expects some kind of Password Container with property Password I m ussing RelayCommands from MVMM Light-Toolkit    public RelayCommand lt object gt  SignIn       get               if  this signIn    null                        this signIn   new RelayCommand lt object gt   passwordContainer    gt                                         var password   passwordContainer GetType   GetProperty  Password   GetValue passwordContainer  as string                      this authenticationService Authenticate this Login  password                                          return this signIn            It can be easily tested with anonymous class   var passwordContainer   new               Password    password

User · Answer

you can do it with attached property  see it   PasswordBox with MVVM

User · Answer

well my answerd is more simple just in the for the MVVM pattern  in class viewmodel  public string password   PasswordChangedCommand   new DelegateCommand lt RoutedEventArgs gt  PasswordChanged    Private void PasswordChanged RoutedEventArgs obj          var e    WatermarkPasswordBox obj OriginalSource         or depending or what are you using      var e    PasswordBox obj OriginalSource       password  e Password       the password property of the PasswordBox that win provides or WatermarkPasswordBox that XCeedtoolkit provides generates an RoutedEventArgs so you can bind it   now in xmal view   lt Xceed WatermarkPasswordBox Watermark  Input your Password  Grid Column  1  Grid ColumnSpan  3  Grid Row  7  PasswordChar      gt            lt i Interaction Triggers gt                lt i EventTrigger EventName  PasswordChanged  gt                    lt prism InvokeCommandAction Command   Binding RelativeSource  RelativeSource AncestorType UserControl   Path  DataContext PasswordChangedCommand   CommandParameter   Binding RelativeSource  RelativeSource Self   Path  Password    gt                lt  i EventTrigger gt            lt  i Interaction Triggers gt        lt  Xceed WatermarkPasswordBox gt    or   lt PasswordBox Grid Column  1  Grid ColumnSpan  3  Grid Row  7  PasswordChar      gt            lt i Interaction Triggers gt                lt i EventTrigger EventName  PasswordChanged  gt                    lt prism InvokeCommandAction Command   Binding RelativeSource  RelativeSource AncestorType UserControl   Path  DataContext PasswordChangedCommand   CommandParameter   Binding RelativeSource  RelativeSource Self   Path  Password    gt                lt  i EventTrigger gt            lt  i Interaction Triggers gt        lt  PasswordBox gt

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I figured I d throw my solution in the mix  since this is such a common issue    and having plenty of options is always a good thing   I simply wrapped a PasswordBox in a UserControl and implemented a DependencyProperty to be able to bind   I m doing everything I can to avoid storing any clear text in the memory  so everything is done through a SecureString and the PasswordBox Password property   During the foreach loop  each character does get exposed  but it s very brief   Honestly  if you re worried about your WPF application to be compromised from this brief exposure  you ve got bigger security issues that should be handled   The beauty of this is that you are not breaking any MVVM rules  even the  purist  ones  since this is a UserControl  so it s allowed to have code-behind   When you re using it  you can have pure communication between View and ViewModel without your VideModel being aware of any part of View or the source of the password   Just make sure you re binding to SecureString in your ViewModel   BindablePasswordBox xaml   lt UserControl x Class  BK WPF CustomControls BindanblePasswordBox               xmlns  http   schemas microsoft com winfx 2006 xaml presentation               xmlns x  http   schemas microsoft com winfx 2006 xaml               xmlns mc  http   schemas openxmlformats org markup-compatibility 2006                xmlns d  http   schemas microsoft com expression blend 2008                mc Ignorable  d  d DesignHeight  22  d DesignWidth  150  gt       lt PasswordBox x Name  PswdBox   gt   lt  UserControl gt    BindablePasswordBox xaml cs  Version 1 - No two-way binding support    using System ComponentModel  using System Security  using System Windows  using System Windows Controls   namespace BK WPF CustomControls       public partial class BindanblePasswordBox   UserControl               public static readonly DependencyProperty PasswordProperty               DependencyProperty Register  Password   typeof SecureString   typeof BindanblePasswordBox             public SecureString Password                       get   return  SecureString GetValue PasswordProperty                 set   SetValue PasswordProperty  value                        public BindanblePasswordBox                         InitializeComponent                PswdBox PasswordChanged    PswdBox PasswordChanged                     private void PswdBox PasswordChanged object sender  RoutedEventArgs e                        var secure   new SecureString                foreach  var c in PswdBox Password                                secure AppendChar c                             Password   secure                      Usage of Version 1    lt local BindanblePasswordBox Width  150  HorizontalAlignment  Center                              VerticalAlignment  Center                              Password   Binding Password  Mode OneWayToSource    gt    BindablePasswordBox xaml cs  Version 2 - Has two-way binding support    public partial class BindablePasswordBox   UserControl       public static readonly DependencyProperty PasswordProperty           DependencyProperty Register  Password   typeof SecureString   typeof BindablePasswordBox           new PropertyMetadata PasswordChanged         public SecureString Password               get   return  SecureString GetValue PasswordProperty             set   SetValue PasswordProperty  value                public BindablePasswordBox                 InitializeComponent            PswdBox PasswordChanged    PswdBox PasswordChanged             private void PswdBox PasswordChanged object sender  RoutedEventArgs e                var secure   new SecureString            foreach  var c in PswdBox Password                        secure AppendChar c                     if  Password    secure                        Password   secure                       private static void PasswordChanged DependencyObject d  DependencyPropertyChangedEventArgs e                var pswdBox   d as BindablePasswordBox          if  pswdBox    null  amp  amp  e NewValue    e OldValue                        var newValue   e NewValue as SecureString              if  newValue    null                                return                             var unmanagedString   IntPtr Zero              string newString              try                               unmanagedString   Marshal SecureStringToGlobalAllocUnicode newValue                   newString   Marshal PtrToStringUni unmanagedString                             finally                               Marshal ZeroFreeGlobalAllocUnicode unmanagedString                              var currentValue   pswdBox PswdBox Password              if  currentValue    newString                                pswdBox PswdBox Password   newString                                    Usage of Version 2    lt local BindanblePasswordBox Width  150  HorizontalAlignment  Center                              VerticalAlignment  Center                              Password   Binding Password  Mode TwoWay    gt

User · Answer

To solve the OP problem without breaking the MVVM  I would use custom value converter and a wrapper for the value  the password  that has to be retrieved from the password box   public interface IWrappedParameter lt T gt        T Value   get       public class PasswordBoxWrapper   IWrappedParameter lt string gt        private readonly PasswordBox  source       public string Value               get   return  source    null    source Password   string Empty               public PasswordBoxWrapper PasswordBox source                 source   source           public class PasswordBoxConverter   IValueConverter       public object Convert object value  Type targetType  object parameter  CultureInfo culture                   Implement type and value check here            return new PasswordBoxWrapper  PasswordBox value              public object ConvertBack object value  Type targetType  object parameter  CultureInfo culture                throw new InvalidOperationException  No conversion               In the view model   public string Username   get  set     public ICommand LoginCommand       get               return new RelayCommand lt IWrappedParameter lt string gt  gt  password   gt    Login Username  password                private void Login string username  string password           Perform login here        Because the view model uses IWrappedParameter lt T gt   it does not need to have any knowledge about PasswordBoxWrapper nor PasswordBoxConverter  This way you can isolate the PasswordBox object from the view model and not break the MVVM pattern   In the view    lt Window Resources gt       lt h PasswordBoxConverter x Key  PwdConverter    gt   lt  Window Resources gt       lt PasswordBox Name  PwdBox    gt   lt Button Content  Login  Command   Binding LoginCommand           CommandParameter   Binding ElementName PwdBox  Converter  StaticResource PwdConverter      gt

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Send a SecureString to the view model using an Attached Behavior and ICommand  There is nothing wrong with code-behind when implementing MVVM  MVVM is an architectural pattern that aims to separate the view from the model business logic  MVVM describes how to achieve this goal in a reproducible way  the pattern   It doesn t care about implementation details  like how do you structure or implement the view  It just draws the boundaries and defines what is the view  the view model and what the model in terms of this pattern s terminology     MVVM doesn t care about the language  XAML or C   or compiler  partial classes   Being language independent is a mandatory characteristic of a design pattern - it must be language neutral   However  code-behind has some draw backs like making your UI logic harder to understand  when it is wildly distributed between XAML and C   But most important implementing UI logic or objects like templates  styles  triggers  animations etc in C  is very complex and ugly less readable than using XAML  XAML is a markup language that uses tags and nesting to visualize object hierarchy  Creating UI using XAML is very convenient  Although there are situations where you are fine choosing to implement UI logic in C   or code-behind   Handling the PasswordBox is one example   For this reasons handling the PasswordBox in the code-behind by handling the PasswordBox PasswordChanged  is no violation of the MVVM pattern   A clear violation would be to pass a control  the PasswordBox  to the view model  Many solutions recommend this e g   bay passing the instance of the PasswordBox as ICommand CommandParameter to the view model  Obviously a very bad and unnecessary recommendation   If you don t care about using C   but just want to keep your code-behind file clean or simply want to encapsulate a behavior UI logic  you can always make use of attached properties and implement an attached behavior    Opposed of the infamous wide spread helper that enables binding to the plain text password  really bad anti-pattern and security risk   this behavior uses an ICommand to send the password as SecureString to the view model  whenever the PasswordBox raises the PasswordBox PasswordChanged event   MainWindow xaml   lt Window gt     lt Window DataContext gt       lt ViewModel   gt     lt  Window DataContext gt      lt PasswordBox PasswordBox Command   Binding VerifyPasswordCommand     gt   lt  Window gt    ViewModel cs  public class ViewModel   INotifyPropertyChanged     public ICommand VerifyPasswordCommand   gt  new RelayCommand VerifyPassword      public void VerifyPassword object commadParameter          if  commandParameter is SecureString secureString              IntPtr valuePtr   IntPtr Zero        try                 valuePtr   Marshal SecureStringToGlobalAllocUnicode value           string plainTextPassword   Marshal PtrToStringUni valuePtr               Handle plain text password              It s recommended to convert the SecureString to plain text in the model  when really needed                 finally                  Marshal ZeroFreeGlobalAllocUnicode valuePtr                         PasswordBox cs     Attached behavior class PasswordBox   DependencyObject      region Command attached property    public static readonly DependencyProperty CommandProperty       DependencyProperty RegisterAttached         Command         typeof ICommand         typeof PasswordBox         new PropertyMetadata default ICommand   PasswordBox OnSendPasswordCommandChanged       public static void SetCommand DependencyObject attachingElement  ICommand value    gt      attachingElement SetValue PasswordBox CommandProperty  value      public static ICommand GetCommand DependencyObject attachingElement    gt       ICommand  attachingElement GetValue PasswordBox CommandProperty       endregion    private static void OnSendPasswordCommandChanged      DependencyObject attachingElement      DependencyPropertyChangedEventArgs e          if    attachingElement is System Windows Controls PasswordBox passwordBox               throw new ArgumentException  Attaching element must be of type  PasswordBox                if  e OldValue    null              return             WeakEventManager lt object  RoutedEventArgs gt  AddHandler        passwordBox        nameof System Windows Controls PasswordBox PasswordChanged         SendPassword OnPasswordChanged          private static void SendPassword OnPasswordChanged object sender  RoutedEventArgs e          var attachedElement   sender as System Windows Controls PasswordBox      SecureString commandParameter   attachedElement  SecurePassword      if  commandParameter    null    commandParameter Length  lt  1              return             ICommand sendCommand   GetCommand attachedElement       sendCommand  Execute commandParameter

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If you want it combined it all in only one control and one command   lt PasswordBox Name  PasswordBoxPin  PasswordChar     gt       lt PasswordBox InputBindings gt           lt KeyBinding Key  Return  Command   Binding AuthentifyEmpCommand   CommandParameter   Binding ElementName PasswordBoxPin    gt       lt  PasswordBox InputBindings gt   lt  PasswordBox gt    And on your Vm  like Konamiman showed   public void AuthentifyEmp object obj        var passwordBox   obj as PasswordBox      var password   passwordBox Password    private RelayCommand  authentifyEmpCommand  public RelayCommand AuthentifyEmpCommand   gt   authentifyEmpCommand      authentifyEmpCommand   new RelayCommand AuthentifyEmp  null      EDIT  Based on comments I feel the need to specify that this is a violation of MVVM pattern  use it only if that is not one of your primary concerns

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This implementation is slightly different  You pass a passwordbox to the View thru binding of a property in ViewModel  it doesn t use any command params  The ViewModel Stays Ignorant of the View   I have a VB vs 2010 Project that can be downloaded from SkyDrive  Wpf MvvM PassWordBox Example zip https   skydrive live com redir aspx cid e95997d33a9f8d73 amp resid E95997D33A9F8D73 511  The way that I am Using PasswordBox in a Wpf MvvM Application is pretty simplistic and works well for Me  That does not mean that I think it is the correct way or the best way  It is just an implementation of Using PasswordBox and the MvvM Pattern   Basicly You create a public readonly property that the View can bind to as a PasswordBox  The actual control  Example   Private  thePassWordBox As PasswordBox Public ReadOnly Property ThePassWordBox As PasswordBox     Get         If IsNothing  thePassWordBox  Then  thePassWordBox   New PasswordBox         Return  thePassWordBox     End Get End Property   I use a backing field just to do the self Initialization of the property   Then From Xaml you bind the Content of a ContentControl or a Control Container Example     lt ContentControl Grid Column  1  Grid Row  1  Height  23  Width  120  Content   Binding Path ThePassWordBox   HorizontalAlignment  Center  VerticalAlignment  Center    gt    From there you have full control of the passwordbox I also use a PasswordAccessor  Just a Function of String  to return the Password Value when doing login or whatever else you want the Password for  In the Example I have a public property in a Generic User Object Model  Example    Public Property PasswordAccessor   As Func Of String    In the User Object the password string property is readonly without any backing store it just returns the Password from the PasswordBox  Example    Public ReadOnly Property PassWord As String     Get         Return If  PasswordAccessor Is Nothing   String Empty  PasswordAccessor Invoke        End Get End Property   Then in the ViewModel I make sure that the Accessor is created and set to the PasswordBox Password  property  Example   Public Sub New        Sets the Accessor for the Password Property     SetPasswordAccessor Function   ThePassWordBox Password  End Sub  Friend Sub SetPasswordAccessor ByVal accessor As Func Of String       If Not IsNothing VMUser  Then VMUser PasswordAccessor   accessor End Sub   When I need the Password string say for login I just get the User Objects Password property that really invokes the Function to grab the password and return it  then the actual password is not stored by the User Object   Example  would be in the ViewModel  Private Function LogIn   as Boolean      Make call to your Authentication methods and or functions  I usally place that code in the Model     Return AuthenticationManager Login New UserIdentity User UserName  User Password  End Function   That should Do It  The ViewModel doesn t need any knowledge of the View s Controls  The View Just binds to property in the ViewModel  not any different than the View Binding to an Image or Other Resource  In this case that resource Property  just happens to be a usercontrol   It allows for testing as the ViewModel creates and owns the Property and the Property is independent of the View  As for Security I don t know how good this implementation is  But by using a Function the Value is not stored in the Property itself just accessed by the Property

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Sorry  but you re doing it wrong   People should have the following security guideline tattooed on the inside of their eyelids  Never keep plain text passwords in memory   The reason the WPF Silverlight PasswordBox doesn t expose a DP for the Password property is security related  If WPF Silverlight were to keep a DP for Password it would require the framework to keep the password itself unencrypted in memory  Which is considered quite a troublesome security attack vector  The PasswordBox uses encrypted memory  of sorts  and the only way to access the password is through the CLR property    I would suggest that when accessing the PasswordBox Password CLR property you d refrain from placing it in any variable or as a value for any property  Keeping your password in plain text on the client machine RAM is a security no-no  So get rid of that public string Password   get  set    you ve got up there    When accessing PasswordBox Password  just get it out and ship it to the server ASAP   Don t keep the value of the password around and don t treat it as you would any other client machine text  Don t keep clear text passwords in memory    I know this breaks the MVVM pattern  but you shouldn t ever bind to PasswordBox Password Attached DP  store your password in the ViewModel or any other similar shenanigans   If you re looking for an over-architected solution  here s one    1  Create the IHavePassword interface with one method that returns the password clear text    2  Have your UserControl implement a IHavePassword interface    3  Register the UserControl instance with your IoC as implementing the IHavePassword interface    4  When a server request requiring your password is taking place  call your IoC for the IHavePassword implementation and only than get the much coveted password   Just my take on it    -- Justin

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You find a solution for the PasswordBox in the ViewModel sample application of the WPF Application Framework  WAF  project   However  Justin is right  Don t pass the password as plain text between View and ViewModel  Use SecureString instead  See MSDN PasswordBox

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You can use this XAML   lt PasswordBox gt       lt i Interaction Triggers gt           lt i EventTrigger EventName  quot PasswordChanged quot  gt               lt i InvokeCommandAction Command  quot  Binding RelativeSource  RelativeSource Mode FindAncestor  AncestorType PasswordBox   quot  CommandParameter  quot  Binding ElementName PasswordBox  quot   gt           lt  i EventTrigger gt       lt  i Interaction Triggers gt   lt  PasswordBox gt   And this command execute method  private void ExecutePasswordChangedCommand PasswordBox obj        if  obj    null       Password   obj Password     This requires adding the System Windows Interactivity assembly to your project and referencing it via xmlns i  quot clr-namespace System Windows Interactivity assembly System Windows Interactivity quot

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A simple solution without violating the MVVM pattern is to introduce an event  or delegate  in the ViewModel that harvests the password   In the ViewModel   public event EventHandler lt HarvestPasswordEventArgs gt  HarvestPassword   with these EventArgs   class HarvestPasswordEventArgs   EventArgs       public string Password      in the View  subscribe to the event on creating the ViewModel and fill in the password value    viewModel HarvestPassword     sender  args    gt       args Password   passwordBox1 Password    In the ViewModel  when you need the password  you can fire the event and harvest the password from there   if  HarvestPassword    null      bah    return   var pwargs   new HarvestPasswordEventArgs    HarvestPassword this  pwargs    LoginHelpers Login Username  pwargs Password

[c#] How to bind to a PasswordBox in MVVM

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