WPF: IsMouseOver trigger not working for datatemplate

Question

I'm trying to get the IsMouseOver trigger working for datatemplate. For some reason it is not firing. I also tried the http://www.wpfmentor.com/2009/01/how-to-debug-triggers-using-trigger.html but I do not see anything in the trace. Here is the code:

XAML:

<Window x:Class="FirstSImpleDataApp.Window4" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="Window4" Height="300" Width="300"> <Window.Resources> <ResourceDictionary> <DataTemplate x:Key="tmptemplate"> <Border x:Name="brd" BorderBrush="Black" BorderThickness="2"> <TextBlock x:Name="txt">my text box</TextBlock> </Border> <DataTemplate.Triggers> <Trigger Property="IsMouseOver" Value="True"> <Setter TargetName="txt" Property="Background" Value="Red"></Setter> <Setter TargetName="txt" Property="Foreground" Value="Green"></Setter> <Setter TargetName="brd" Property="Background" Value="Green"></Setter> </Trigger> </DataTemplate.Triggers> </DataTemplate> </ResourceDictionary> </Window.Resources> <Canvas x:Name="can" Loaded="can_Loaded"> </Canvas> </Window>

Code behind:

 public partial class Window4 : Window { public Window4() { InitializeComponent(); } private void can_Loaded(object sender, RoutedEventArgs e) { var tmp = this.TryFindResource("tmptemplate") as DataTemplate; var obj = (FrameworkElement)tmp.LoadContent(); can.Children.Add(obj); } }

Any help is appreciated!

Mike Strobel · Accepted Answer · 2014-10-31 18:31:41Z

1

Your triggers actually work just fine. The problem is with how you're instantiating the template and adding it to your Canvas programmatically.

Apply the template directly in your Xaml to see it work:

<Canvas x:Name="can"> <ContentControl ContentTemplate="{StaticResource tmptemplate}" /> </Canvas>

If you want to apply it programmatically, apply the template to a ContentControl or ContentPresenter and drop it in the Canvas instead:

private void can_Loaded(object sender, RoutedEventArgs e) { var tmp = this.TryFindResource("tmptemplate") as DataTemplate; can.Children.Add(new ContentPresenter { ContentTemplate = tmp }); }

edited Oct 31, 2014 at 18:31

answered Oct 31, 2014 at 17:47

Mike Strobel

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8 Comments

King King Over a year ago

Well just tried this with a simple Button (its ContentTemplate is set to this template), the behavior is a little different, which may not be what the OP wants. The trigger is just fired when hovering over the inner Border, that Border is not stretched to fill the Button. So if the OP wants that hovering the Button should fire the Trigger, this of course does not work as desired unless there may be some tweak for it.

May Over a year ago

@Mike, I cannot do it in xaml because in the real project, I instantiate lot of these objects and place it on canvas. And these are dynamic, so I need to create them in xaml.

May Over a year ago

Thanks Mike. That worked like charm. Can you please explain the technical reason?

Mike Strobel Over a year ago

It seems like LoadContent only instantiates the visual tree, and does not attach a name scope, apply triggers, or anything else. I don't think it's meant to be used the way you were using it. Digging through the WPF code, the way data templates are applied is far more involved, but most of the methods are internal.

May Over a year ago

Hi Mike, after changing over to ContentControl, it is not passing down the DataContext to inner controls. Do you know how can I get it working?

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MikeG · Accepted Answer · 2014-10-31 17:41:16Z

Here is an alternative using Style triggers. The border remains black, but with a green margin from the TextBlock.

 <Style TargetType="TextBlock"> <Style.Triggers> <Trigger Property="IsMouseOver" Value="True"> <Setter Property="Background" Value="Red"/> <Setter Property="Foreground" Value="Green"/> <Setter Property="Margin" Value="2"/> </Trigger> </Style.Triggers> </Style> <Style TargetType="Border"> <Style.Triggers> <Trigger Property="IsMouseOver" Value="True"> <Setter Property="Background" Value="Green"/> </Trigger> </Style.Triggers> </Style> <Border BorderThickness="1" BorderBrush="Black"> <TextBlock Text="My Text Block"/> </Border>

I would like to avoid having to add style triggers. Is there another way?

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