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POSetter in property trigger fails if target property already has an explicit value
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  1. POSetter in property trigger fails if target property already has an explicit value
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    copied!<p>I'm currently trying to create a <code>ControlTemplate</code> for the <code>Button</code> class in WPF, replacing the usual visual tree with something that makes the button look similar to the little (X) close icon on Google Chrome's tabs. I decided to use a <code>Path</code> object in XAML to achieve the effect. Using a property trigger, the control responds to a change in the IsMouseOver property by setting the icon's red background.</p> <p>Here's the XAML from a test app:</p> <pre><code>&lt;Window x:Class="Widgets.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="Window1" Height="300" Width="300"&gt; &lt;Window.Resources&gt; &lt;Style x:Key="borderStyle" TargetType="Border"&gt; &lt;Style.Triggers&gt; &lt;Trigger Property="IsMouseOver" Value="True"&gt; &lt;Setter Property="Background"&gt; &lt;Setter.Value&gt; &lt;SolidColorBrush Color="#CC0000"/&gt; &lt;/Setter.Value&gt; &lt;/Setter&gt; &lt;/Trigger&gt; &lt;/Style.Triggers&gt; &lt;/Style&gt; &lt;ControlTemplate x:Key="closeButtonTemplate" TargetType="Button"&gt; &lt;Border Width="12" Height="12" CornerRadius="6" BorderBrush="#AAAAAA" Background="Transparent" Style="{StaticResource borderStyle}" ToolTip="Close"&gt; &lt;Viewbox Margin="2.75"&gt; &lt;Path Data="M 0,0 L 10,10 M 0,10 L 10,0" Stroke="{Binding BorderBrush, RelativeSource={RelativeSource FindAncestor, AncestorType=Border, AncestorLevel=1}}" StrokeThickness="1.8"/&gt; &lt;/Viewbox&gt; &lt;/Border&gt; &lt;/ControlTemplate&gt; &lt;/Window.Resources&gt; &lt;Grid Background="White"&gt; &lt;Button Template="{StaticResource closeButtonTemplate}"/&gt; &lt;/Grid&gt; &lt;/Window&gt; </code></pre> <p>Note that the circular background is always there - it's just transparent when the mouse isn't over it.</p> <p>The problem with this is that the trigger just isn't working. Nothing changes in the button's appearance. However, if I remove the <code>Background="Transparent"</code> value from the <code>Border</code> object in the <code>ControlTemplate</code>, the trigger <em>does</em> work (albeit only when over the 'X').</p> <p>I really can't explain this. Setters for any other properties placed in the <code>borderStyle</code> resource work fine, but the <code>Background</code> setter fails as soon as the default background is specified in the <code>ControlTemplate</code>.</p> <p>Any ideas why it's happening and how I can fix it? I know I could easily replace this code with, for example, a .PNG-based image, but I want to understand why the current implementation isn't working.</p> <p>Thanks! :)</p>
 

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