Style.Trigger vs. Grid.Trigger - wpf

Question

In my Code I have defined two Triggers, a Label and a Canvas.
The description of my problem:
When the cursor goes straight across the Label, the Style.Trigger gets activated and the background colour changes (to orange). When the cursor runs across the canvas-area the Grid.Trigger gets activated and changes the background color(to violet). So far, so good.Is the cursor now, running (after the Grid.Trigger was active) across the label-area the background does not change at all.
It seems to me that the Grid.Trigger gets priority once it was active.
<Window x:Class="Sample01.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Grid>
<Grid.Resources>
<!-- Defined Style starts here -->
<Style x:Key="{x:Type Label}" TargetType="{x:Type Label}" >
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Trigger.Setters>
</Trigger.Setters>
<Trigger.EnterActions>
<BeginStoryboard>
<Storyboard>
<ColorAnimation To="DarkOrange" Duration="0:0:0.5"
Storyboard.TargetProperty="Background.Color"
/>
</Storyboard>
</BeginStoryboard>
</Trigger.EnterActions>
<Trigger.ExitActions>
<BeginStoryboard>
<Storyboard>
<ColorAnimation To="White" Duration="0:0:1"
Storyboard.TargetProperty="Background.Color" />
</Storyboard>
</BeginStoryboard>
</Trigger.ExitActions>
</Trigger>
</Style.Triggers>
</Style>
<!-- End defined Style-->
</Grid.Resources>
<!-- Define Trigger -->
<Grid.Triggers>
<EventTrigger RoutedEvent="MouseEnter"
SourceName="canvas">
<BeginStoryboard>
<Storyboard>
<ColorAnimation To="BlueViolet" Duration="0:0:1"
Storyboard.TargetProperty="Background.Color"
Storyboard.TargetName="label" />
</Storyboard>
</BeginStoryboard>
</EventTrigger>
<EventTrigger RoutedEvent="MouseLeave"
SourceName="canvas">
<BeginStoryboard>
<Storyboard>
<ColorAnimation To="White" Duration="0:0:1"
Storyboard.TargetProperty="Background.Color"
Storyboard.TargetName="label" />
</Storyboard>
</BeginStoryboard>
</EventTrigger>
</Grid.Triggers>
<Label x:Name="label" VerticalAlignment="Top" Height="100" BorderBrush="Black" BorderThickness="2" Content="LABEL"/>
<Canvas x:Name="canvas" Height="100" VerticalAlignment="Bottom"
IsHitTestVisible="True"
Background="AntiqueWhite"
/>
</Grid>
Can someone explain this behavior ?

Answer 1

You're running into the order of precedence of value sources for Dependency Properties. A common case of this is when you set a local value directly on an element, a value set in a style is overridden. In this case, you're applying an animation to the property, which takes precedence over anything set in the Style (or even a local value).
To allow the Style to take over again you need to make the animation no longer apply to the Label. You can do this by explicitly removing the initial animation, which will reset back to the original state, like a Property Trigger does:
<EventTrigger RoutedEvent="FrameworkElement.MouseEnter"
SourceName="canvas">
<BeginStoryboard x:Name="GridMouseover">
<Storyboard>
<ColorAnimation To="BlueViolet" Duration="0:0:1"
Storyboard.TargetProperty="Background.Color"
Storyboard.TargetName="label" />
</Storyboard>
</BeginStoryboard>
</EventTrigger>
<EventTrigger RoutedEvent="FrameworkElement.MouseLeave"
SourceName="canvas">
<RemoveStoryboard BeginStoryboardName="GridMouseover"/>
</EventTrigger>
The disadvantage of this is that you lose the smooth animation back to White. VisualStateManager is a much better choice for this kind of thing in many cases because it handles that for you automatically.
The other thing you can do is tell the Storyboard to stop applying itself after finishing by changing the FillBehavior:
<EventTrigger RoutedEvent="FrameworkElement.MouseEnter"
SourceName="canvas">
<BeginStoryboard>
<Storyboard>
<ColorAnimation To="BlueViolet" Duration="0:0:1"
Storyboard.TargetProperty="Background.Color"
Storyboard.TargetName="label" />
</Storyboard>
</BeginStoryboard>
</EventTrigger>
<EventTrigger RoutedEvent="FrameworkElement.MouseLeave"
SourceName="canvas">
<BeginStoryboard>
<Storyboard FillBehavior="Stop">
<ColorAnimation To="White" Duration="0:0:1"
Storyboard.TargetProperty="Background.Color"
Storyboard.TargetName="label" />
</Storyboard>
</BeginStoryboard>
</EventTrigger>