My Custom Event does not produce anything

Question

I'm trying to create custom RoutedEvent in order to trigger an animation whenever the Text property of a TextBlock changes. My class inherits from TextBlock class and I shadow the Text property. I'm using a Button in order to change the Text property in some other value. My code does not produce any errors but it doesn't do anything. I'm sure that the problem is with the TextChanged event because when I replace it with let's say MouseEnter event, everything works ok.

Public Class MyCustomTextBlock
Inherits TextBlock

Public Shared ReadOnly TextChangedEvent As RoutedEvent = EventManager.RegisterRoutedEvent("TextChanged", _
               RoutingStrategy.Bubble, GetType(RoutedEventArgs), GetType(MyCustomTextBlock))

Public Custom Event TextChanged As RoutedEventHandler
    AddHandler(ByVal value As RoutedEventHandler)
        Me.AddHandler(TextChangedEvent, value)
    End AddHandler

    RemoveHandler(ByVal value As RoutedEventHandler)
        Me.RemoveHandler(TextChangedEvent, value)
    End RemoveHandler

    RaiseEvent(ByVal sender As Object, ByVal e As System.Windows.RoutedEventArgs)
        Me.RaiseEvent(e)
    End RaiseEvent
End Event

Public Shared Shadows TextProperty As DependencyProperty =
    DependencyProperty.Register("Text", GetType(String), GetType(MyCustomTextBlock),
                                 New FrameworkPropertyMetadata(String.Empty,
                                    New PropertyChangedCallback(AddressOf TextPropertyChanged)))

Private Shared Sub TextPropertyChanged(ByVal sender As Object, ByVal e As DependencyPropertyChangedEventArgs)
    DirectCast(sender, MyCustomTextBlock).RaiseEvent(New RoutedEventArgs(MyCustomTextBlock.TextChangedEvent))
End Sub
End Class

XAML

<Window x:Class="MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WpfApplication1"   
    Title="MainWindow" Height="350" Width="525">

<Window.Resources>
    <Style TargetType="local:MyCustomTextBlock">
        <Style.Triggers>
            <EventTrigger RoutedEvent="local:MyCustomTextBlock.TextChanged">
                <EventTrigger.Actions>
                    <BeginStoryboard>
                        <Storyboard>
                            <DoubleAnimation Storyboard.TargetProperty="FontSize" To="30" Duration="0:0:1" />
                        </Storyboard>
                    </BeginStoryboard>
                </EventTrigger.Actions>
            </EventTrigger>
        </Style.Triggers>
    </Style>       
</Window.Resources>

<Grid>
    <local:MyCustomTextBlock x:Name="Textblock1" Text="xxxxxxxxx" Background="Yellow" Width="100" Height="25" />
    <Button Content="Change Text" Height="23" HorizontalAlignment="Left" Margin="217,218,0,0" Name="Button1" VerticalAlignment="Top" Width="75" />
</Grid>

Class Main Window       
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As      
System.Windows.RoutedEventArgs) Handles Button1.Click

    Textblock1.Text = "apollon"
End Sub
End Class

score 0 · Accepted Answer · answered May 09 '13 at 15:31

It looks like the problem is that you're creating new members that conflict with those on the base TextBox. You should consider using the TextChanged event that already exists on TextBox, or if you do need your own, name it something different. Here so far you aren't doing anything that the base properties don't do for you already.

The main issue with your specific question though appears to be with the new TextProperty that you created. You shouldn't hide a dependency property on a base class, primarily because you can't control which one will be used in every situation, but also because there are mechanisms built in to make it unnecessary. In your case you've aggravated the problem by not fully implementing the boilerplate code for a DP. Because you have no wrapper property, your setting of the Text property from code is setting TextBox.Text, which internally is calling SetValue with TextBox.TextProperty, hence skipping your code entirely.

Instead of declaring your own TextProperty you can just tack on your metadata to the existing one. To add a change handler to the existing property add this call into a static constructor:

        TextProperty.OverrideMetadata(GetType(MyCustomTextBlock),
                             New FrameworkPropertyMetadata(String.Empty,
                             New PropertyChangedCallback(AddressOf TextPropertyChanged)))

Thanks for your response! I'm using Textblock not Textbox...so there is no TextChanged event at the base Class. — apollon, May 09 '13 at 18:23
So I tried your code and it works fine. Thanks a lot excellent post! — apollon, May 09 '13 at 21:22

My Custom Event does not produce anything

1 Answers1