Setting a property with an EventTrigger

Question

I want to be able to set a property with an EventTrigger  there s a number of problems with this   1   EventTriggers only support Actions  so I must use a storyBoard to set my properties   2   Once I use a storyboard  I have two options    Stop   Once the animation has stopped the value reverts back to before the animation started HoldEnd   This locks the property  so that neither code  nor user interaction can change the property that the animation is holding    In the below example  I want to set the IsChecked property to False when the button is clicked and I want the user to be able to change the IsChecked and or I want to be able to change the property in code   Example    lt EventTrigger     SourceName  myButton      RoutedEvent  Button Click  gt       lt EventTrigger Actions gt           lt BeginStoryboard gt               lt Storyboard gt                   lt BooleanAnimationUsingKeyFrames                     Storyboard TargetName  myCheckBox                      Storyboard TargetProperty  IsChecked                      FillBehavior  Stop  gt                       lt DiscreteBooleanKeyFrame                         KeyTime  00 00 00                          Value  False    gt                   lt  BooleanAnimationUsingKeyFrames gt               lt  Storyboard gt           lt  BeginStoryboard gt       lt  EventTrigger Actions gt   lt  EventTrigger gt    I realize that I can use the  Completed  event after the storyboard completes to set the value to False   However  in this instance I want to contain the logic within the XAML  as this logic will be used on a custom control and is only specific to the UI

User · Accepted Answer

As much as I love XAML  for this kinds of tasks I switch to code behind  Attached behaviors are a good pattern for this  Keep in mind  Expression Blend 3 provides a standard way to program and use behaviors  There are a few existing ones on the Expression Community Site

User · Answer

Stopping the Storyboard can be done in the code behind  or the xaml  depending on where the need comes from   If the EventTrigger is moved outside of the button  then we can go ahead and target it with another EventTrigger that will tell the storyboard to stop   When the storyboard is stopped in this manner it will not revert to the previous value   Here I ve moved the Button Click EventTrigger to a surrounding StackPanel and added a new EventTrigger on the the CheckBox Click to stop the Button s storyboard when the CheckBox is clicked   This lets us check and uncheck the CheckBox when it is clicked on and gives us the desired unchecking behavior from the button as well        lt StackPanel x Name  myStackPanel  gt            lt CheckBox x Name  myCheckBox                    Content  My CheckBox    gt            lt Button Content  Click to Uncheck                  x Name  myUncheckButton    gt            lt Button Content  Click to check the box in code                   Click  OnClick    gt            lt StackPanel Triggers gt                lt EventTrigger RoutedEvent  Button Click                            SourceName  myUncheckButton  gt                   lt EventTrigger Actions gt                       lt BeginStoryboard x Name  myBeginStoryboard  gt                           lt Storyboard x Name  myStoryboard  gt                               lt BooleanAnimationUsingKeyFrames Storyboard TargetName  myCheckBox                                                              Storyboard TargetProperty  IsChecked  gt                                   lt DiscreteBooleanKeyFrame KeyTime  00 00 00                                                           Value  False    gt                               lt  BooleanAnimationUsingKeyFrames gt                           lt  Storyboard gt                       lt  BeginStoryboard gt                   lt  EventTrigger Actions gt               lt  EventTrigger gt                lt EventTrigger RoutedEvent  CheckBox Click                            SourceName  myCheckBox  gt                   lt EventTrigger Actions gt                       lt StopStoryboard BeginStoryboardName  myBeginStoryboard    gt                   lt  EventTrigger Actions gt               lt  EventTrigger gt            lt  StackPanel Triggers gt       lt  StackPanel gt    To stop the storyboard in the code behind  we will have to do something slightly different   The third button provides the method where we will stop the storyboard and set the IsChecked property back to true through code   We can t call myStoryboard Stop   because we did not begin the Storyboard through the code setting the isControllable parameter   Instead  we can remove the Storyboard   To do this we need the FrameworkElement that the storyboard exists on  in this case our StackPanel   Once the storyboard is removed  we can once again set the IsChecked property with it persisting to the UI       private void OnClick object sender  RoutedEventArgs e                myStoryboard Remove myStackPanel           myCheckBox IsChecked   true

User · Answer

Just create your own action   namespace WpfUtil       using System Reflection      using System Windows      using System Windows Interactivity             lt summary gt          Sets the designated property to the supplied value  TargetObject         optionally designates the object on which to set the property  If         TargetObject is not supplied then the property is set on the object         to which the trigger is attached           lt  summary gt      public class SetPropertyAction   TriggerAction lt FrameworkElement gt                   PropertyName DependencyProperty                lt summary gt              The property to be executed in response to the trigger               lt  summary gt          public string PropertyName                       get   return  string GetValue PropertyNameProperty                 set   SetValue PropertyNameProperty  value                        public static readonly DependencyProperty PropertyNameProperty               DependencyProperty Register  PropertyName   typeof string               typeof SetPropertyAction                 PropertyValue DependencyProperty                lt summary gt              The value to set the property to               lt  summary gt          public object PropertyValue                       get   return GetValue PropertyValueProperty                 set   SetValue PropertyValueProperty  value                        public static readonly DependencyProperty PropertyValueProperty               DependencyProperty Register  PropertyValue   typeof object               typeof SetPropertyAction                 TargetObject DependencyProperty                lt summary gt              Specifies the object upon which to set the property               lt  summary gt          public object TargetObject                       get   return GetValue TargetObjectProperty                 set   SetValue TargetObjectProperty  value                        public static readonly DependencyProperty TargetObjectProperty               DependencyProperty Register  TargetObject   typeof object               typeof SetPropertyAction                 Private Implementation           protected override void Invoke object parameter                        object target   TargetObject    AssociatedObject              PropertyInfo propertyInfo   target GetType   GetProperty                  PropertyName                  BindingFlags Instance BindingFlags Public                  BindingFlags NonPublic BindingFlags InvokeMethod                propertyInfo SetValue target  PropertyValue                       In this case I m binding to a property called DialogResult on my viewmodel      lt Grid gt        lt Button gt           lt i Interaction Triggers gt               lt i EventTrigger EventName  Click  gt                   lt wpf SetPropertyAction PropertyName  DialogResult  TargetObject   Binding                                          PropertyValue   x Static mvvm DialogResult Cancel    gt               lt  i EventTrigger gt           lt  i Interaction Triggers gt          Cancel      lt  Button gt    lt  Grid gt

User · Answer

I modified Neutrino s solution to make the xaml look less verbose when specifying the value   Sorry for no pictures of the rendered xaml  just imagine a     hamburger button that you click and it turns into   lt -  a back button and also toggles the visibility of a Grid   xmlns i  clr-namespace System Windows Interactivity assembly System Windows Interactivity         lt Grid gt       lt Button x Name  optionsButton  gt           lt i Interaction Triggers gt               lt i EventTrigger EventName  Click  gt                   lt local SetterAction PropertyName  Visibility  Value  Collapsed    gt                   lt local SetterAction PropertyName  Visibility  TargetObject   Binding ElementName optionsBackButton   Value  Visible    gt                   lt local SetterAction PropertyName  Visibility  TargetObject   Binding ElementName optionsPanel   Value  Visible    gt               lt  i EventTrigger gt           lt  i Interaction Triggers gt            lt glyphs Hamburger Width  10  Height  10    gt       lt  Button gt        lt Button x Name  optionsBackButton  Visibility  Collapsed  gt           lt i Interaction Triggers gt               lt i EventTrigger EventName  Click  gt                   lt local SetterAction PropertyName  Visibility  Value  Collapsed    gt                   lt local SetterAction PropertyName  Visibility  TargetObject   Binding ElementName optionsButton   Value  Visible    gt                   lt local SetterAction PropertyName  Visibility  TargetObject   Binding ElementName optionsPanel   Value  Collapsed    gt               lt  i EventTrigger gt           lt  i Interaction Triggers gt            lt glyphs Back Width  12  Height  11    gt       lt  Button gt   lt  Grid gt         lt Grid Grid RowSpan  2  x Name  optionsPanel  Visibility  Collapsed  gt    lt  Grid gt    You can also specify values this way like in Neutrino s solution    lt Button x Name  optionsButton  gt       lt i Interaction Triggers gt           lt i EventTrigger EventName  Click  gt               lt local SetterAction PropertyName  Visibility  Value   x Static Visibility Collapsed     gt               lt local SetterAction PropertyName  Visibility  TargetObject   Binding ElementName optionsBackButton   Value   x Static Visibility Visible     gt               lt local SetterAction PropertyName  Visibility  TargetObject   Binding ElementName optionsPanel   Value   x Static Visibility Visible     gt           lt  i EventTrigger gt       lt  i Interaction Triggers gt        lt glyphs Hamburger Width  10  Height  10    gt   lt  Button gt    And here s the code   using System  using System ComponentModel  using System Reflection  using System Windows  using System Windows Interactivity   namespace Mvvm Actions            lt summary gt          Sets a specified property to a value when invoked           lt  summary gt      public class SetterAction   TargetedTriggerAction lt FrameworkElement gt                 region Properties           region PropertyName               lt summary gt              Property that is being set by this setter               lt  summary gt          public string PropertyName                       get   return  string GetValue PropertyNameProperty                 set   SetValue PropertyNameProperty  value                        public static readonly DependencyProperty PropertyNameProperty               DependencyProperty Register  PropertyName   typeof string   typeof SetterAction               new PropertyMetadata String Empty              endregion           region Value               lt summary gt              Property value that is being set by this setter               lt  summary gt          public object Value                       get   return  object GetValue ValueProperty                 set   SetValue ValueProperty  value                        public static readonly DependencyProperty ValueProperty               DependencyProperty Register  Value   typeof object   typeof SetterAction               new PropertyMetadata null              endregion           endregion           region Overrides          protected override void Invoke object parameter                        var target   TargetObject    AssociatedObject               var targetType   target GetType                 var property   targetType GetProperty PropertyName  BindingFlags NonPublic   BindingFlags Public   BindingFlags Static   BindingFlags Instance               if  property    null                  throw new ArgumentException String Format  Property not found   0    PropertyName                 if  property CanWrite    false                  throw new ArgumentException String Format  Property is not settable   0    PropertyName                 object convertedValue               if  Value    null                  convertedValue   null               else                               var valueType   Value GetType                    var propertyType   property PropertyType                   if  valueType    propertyType                      convertedValue   Value                   else                                       var propertyConverter   TypeDescriptor GetConverter propertyType                        if  propertyConverter CanConvertFrom valueType                           convertedValue   propertyConverter ConvertFrom Value                        else if  valueType IsSubclassOf propertyType                           convertedValue   Value                       else                         throw new ArgumentException String Format  Cannot convert type   0   to   1      valueType  propertyType                                                 property SetValue target  convertedValue                       endregion

[wpf] Setting a property with an EventTrigger

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