How To Raise Property Changed events on a Dependency Property

Question

I have a control with two properties  One is a DependencyProperty  the other is an  alias  to the first one   How do I raise the PropertyChanged event for the second one  the alias  when the first one is changed   NOTE  I m using DependencyObjects  not INotifyPropertyChanged  tried that  didn t work because my control is a ListVie sub-classed   Something like this       protected override void OnPropertyChanged DependencyPropertyChangedEventArgs e        base OnPropertyChanged e       if  e Property    MyFirstProperty                RaiseAnEvent  MySecondProperty        what is the code that would go here                If I were using an INotify I could do like this     public string SecondProperty       get               return this m IconPath           public string IconPath       get               return this m IconPath            set               if  this m IconPath    value                        this m IconPath   value          this SendPropertyChanged  IconPath            this SendPropertyChanged  SecondProperty                        Where can I raise PropertyChanged events on multiple properties from one setter   I need to be able to do the same thing  only using DependencyProperties

User · Answer

I question the logic of raising a PropertyChanged event on the second property when it s the first property that s changing   If the second properties value changes then the PropertyChanged event could be raised there   At any rate  the answer to your question is you should implement INotifyPropertyChange  This interface contains the PropertyChanged event  Implementing INotifyPropertyChanged lets other code know that the class has the PropertyChanged event  so that code can hook up a handler  After implementing INotifyPropertyChange  the code that goes in the if statement of your OnPropertyChanged is   if  PropertyChanged    null      PropertyChanged new PropertyChangedEventArgs  MySecondProperty

User · Answer

I think the OP is asking the wrong question  The code below will show that it not necessary to manually raise the PropertyChanged EVENT from a dependency property to achieve the desired result  The way to do it is handle the PropertyChanged CALLBACK on the dependency property and set values for other dependency properties there  The following is a working example  In the code below  MyControl has two dependency properties - ActiveTabInt and ActiveTabString  When the user clicks the button on the host  MainWindow   ActiveTabString is modified  The PropertyChanged CALLBACK on the dependency property sets the value of ActiveTabInt  The PropertyChanged EVENT is not manually raised by MyControl   MainWindow xaml cs       lt summary gt      Interaction logic for MainWindow xaml      lt  summary gt  public partial class MainWindow   Window  INotifyPropertyChanged       public MainWindow                 InitializeComponent            DataContext   this          ActiveTabString    zero              private string  ActiveTabString      public string ActiveTabString               get   return  ActiveTabString            set                       if   ActiveTabString    value                                 ActiveTabString   value                  RaisePropertyChanged  ActiveTabString                                       private int  ActiveTabInt      public int ActiveTabInt               get   return  ActiveTabInt            set                       if   ActiveTabInt    value                                 ActiveTabInt   value                  RaisePropertyChanged  ActiveTabInt                                        region INotifyPropertyChanged implementation     public event PropertyChangedEventHandler PropertyChanged       public void RaisePropertyChanged string propertyName                if  PropertyChanged    null              PropertyChanged this  new PropertyChangedEventArgs propertyName               endregion      private void Button Click object sender  RoutedEventArgs e                ActiveTabString    ActiveTabString     zero      one     zero             public class MyControl   Control       public static List lt string gt  Indexmap   new List lt string gt  new string      zero    one            public string ActiveTabString               get   return  string GetValue ActiveTabStringProperty             set   SetValue ActiveTabStringProperty  value                public static readonly DependencyProperty ActiveTabStringProperty   DependencyProperty Register           ActiveTabString           typeof string           typeof MyControl   new FrameworkPropertyMetadata              null              FrameworkPropertyMetadataOptions BindsTwoWayByDefault              ActiveTabStringChanged          public int ActiveTabInt               get   return  int GetValue ActiveTabIntProperty             set   SetValue ActiveTabIntProperty  value               public static readonly DependencyProperty ActiveTabIntProperty   DependencyProperty Register           ActiveTabInt           typeof Int32           typeof MyControl   new FrameworkPropertyMetadata              new Int32                FrameworkPropertyMetadataOptions BindsTwoWayByDefault          static MyControl                 DefaultStyleKeyProperty OverrideMetadata typeof MyControl   new FrameworkPropertyMetadata typeof MyControl                 public override void OnApplyTemplate                 base OnApplyTemplate                private static void ActiveTabStringChanged DependencyObject sender  DependencyPropertyChangedEventArgs e                MyControl thiscontrol   sender as MyControl           if  Indexmap thiscontrol ActiveTabInt     thiscontrol ActiveTabString              thiscontrol ActiveTabInt   Indexmap IndexOf e NewValue ToString                MainWindow xaml       lt StackPanel Orientation  Vertical  gt       lt Button Content  Change Tab Index  Click  Button Click  Width  110  Height  30  gt  lt  Button gt       lt local MyControl x Name  myControl  ActiveTabInt   Binding ActiveTabInt  Mode TwoWay   ActiveTabString   Binding ActiveTabString   gt  lt  local MyControl gt   lt  StackPanel gt    App xaml   lt Style TargetType  local MyControl  gt           lt Setter Property  Template  gt               lt Setter Value gt                   lt ControlTemplate TargetType  local MyControl  gt                       lt TabControl SelectedIndex   Binding ActiveTabInt  Mode TwoWay   gt                           lt TabItem Header  Tab Zero  gt                               lt TextBlock Text   Binding ActiveTabInt   gt  lt  TextBlock gt                           lt  TabItem gt                           lt TabItem Header  Tab One  gt                               lt TextBlock Text   Binding ActiveTabInt   gt  lt  TextBlock gt                           lt  TabItem gt                       lt  TabControl gt                   lt  ControlTemplate gt               lt  Setter Value gt           lt  Setter gt       lt  Style gt

User · Answer

Implement INotifyPropertyChanged in your class  Specify a callback in the property metadata when you register the dependency property  In the callback  raise the PropertyChanged event    Adding the callback   public static DependencyProperty FirstProperty   DependencyProperty Register     First      typeof string      typeof MyType     new FrameworkPropertyMetadata       false        new PropertyChangedCallback OnFirstPropertyChanged       Raising PropertyChanged in the callback   private static void OnFirstPropertyChanged     DependencyObject sender  DependencyPropertyChangedEventArgs e       PropertyChangedEventHandler h   PropertyChanged     if  h    null             h sender  new PropertyChangedEventArgs  Second

User · Answer

I agree with Sam and Xaser and have actually taken this a bit farther  I don t think you should be implementing the INotifyPropertyChanged interface in a UserControl at all   the control is already a DependencyObject and therefore already comes with notifications  Adding INotifyPropertyChanged to a DependencyObject is redundant and  smells  wrong to me   What I did is implement both properties as DependencyProperties  as Sam suggests  but then simply had the PropertyChangedCallback from the  first  dependency property alter the value of the  second  dependency property  Since both are dependency properties  both will automatically raise change notifications to any interested subscribers  e g  data binding etc    In this case  dependency property A is the string InviteText  which triggers a change in dependency property B  the Visibility property named ShowInvite  This would be a common use case if you have some text that you want to be able to hide completely in a control via data binding   public string InviteText         get   return  string GetValue InviteTextProperty         set   SetValue InviteTextProperty  value        public static readonly DependencyProperty InviteTextProperty       DependencyProperty Register  InviteText   typeof string   typeof InvitePrompt   new UIPropertyMetadata String Empty  OnInviteTextChanged     private static void OnInviteTextChanged DependencyObject d  DependencyPropertyChangedEventArgs e        InvitePrompt prompt   d as InvitePrompt      if  prompt    null                string text   e NewValue as String          prompt ShowInvite   String IsNullOrWhiteSpace text    Visibility Collapsed   Visibility Visible           public Visibility ShowInvite       get   return  Visibility GetValue ShowInviteProperty         set   SetValue ShowInviteProperty  value        public static readonly DependencyProperty ShowInviteProperty       DependencyProperty Register  ShowInvite   typeof Visibility   typeof InvitePrompt   new PropertyMetadata Visibility Collapsed      Note I m not including the UserControl signature or constructor here because there is nothing special about them  they don t need to subclass from INotifyPropertyChanged at all

User · Answer

I ran into a similar problem where I have a dependency property that I wanted the class to listen to change events to grab related data from a service   public static readonly DependencyProperty CustomerProperty        DependencyProperty Register  Customer   typeof Customer           typeof CustomerDetailView           new PropertyMetadata OnCustomerChangedCallBack     public Customer Customer       get   return  Customer GetValue CustomerProperty         set   SetValue CustomerProperty  value        private static void OnCustomerChangedCallBack          DependencyObject sender  DependencyPropertyChangedEventArgs e        CustomerDetailView c   sender as CustomerDetailView      if  c    null            c OnCustomerChanged             protected virtual void OnCustomerChanged            Grab related data         Raises INotifyPropertyChanged PropertyChanged     OnPropertyChanged  Customer

[wpf] How To Raise Property Changed events on a Dependency Property?

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