Wpf – How to set MouseOver event/trigger for border in XAML

triggerswpfxaml

I want the border to turn green when the mouse is over it and then to return to blue when the mouse is no longer over the border.

I attempted this without any luck:

<Border 
    Name="ClearButtonBorder" 
    Grid.Column="1" 
    CornerRadius="0,3,3,0" 
    Background="Blue">
    <Border.Triggers>
        <Trigger Property="Border.IsMouseOver" Value="True">
            <Setter Property="Border.Background" Value="Green" />
        </Trigger>
        <Trigger Property="Border.IsMouseOver" Value="False">
            <Setter Property="Border.Background" Value="Blue" />
        </Trigger>
    </Border.Triggers>
    <TextBlock 
        HorizontalAlignment="Center" 
        VerticalAlignment="Center" 
        Text="X" />
</Border>

How can one set a trigger or events for MouseOver?

Best Answer

Yes, this is confusing...

According to this blog post, it looks like this is an omission from WPF.

To make it work you need to use a style:

    <Border Name="ClearButtonBorder" Grid.Column="1" CornerRadius="0,3,3,0">
        <Border.Style>
            <Style>
                <Setter Property="Border.Background" Value="Blue"/>
                <Style.Triggers>
                    <Trigger Property="Border.IsMouseOver" Value="True">
                        <Setter Property="Border.Background" Value="Green" />
                    </Trigger>
                </Style.Triggers>
            </Style>
        </Border.Style>
        <TextBlock HorizontalAlignment="Center" VerticalAlignment="Center" Text="X" />
    </Border>

I guess this problem isn't that common as most people tend to factor out this sort of thing into a style, so it can be used on multiple controls.

Related Solutions

R – Using WPF, what is the best method to update the background for a custom button control

In your ControlTemplate, give the Border a Name and you can then reference that part of its visual tree in the triggers. Here's a very brief example of restyling a normal Button:

<Style
    TargetType="{x:Type Button}">
    <Setter
        Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type Button}">
                <Border Name="customBorder"
                    CornerRadius="5"
                    BorderThickness="1"
                    BorderBrush="Black"
                    Background="{StaticResource normalButtonBG}">
                    <ContentPresenter
                        HorizontalAlignment="Center"
                        VerticalAlignment="Center" />
                </Border>
                <ControlTemplate.Triggers>
                    <Trigger
                        Property="IsMouseOver"
                        Value="True">
                        <Setter
                            TargetName="customBorder"
                            Property="Background"
                            Value="{StaticResource hoverButtonBG}" />
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

If that doesn't help, we'll need to know more, probably seeing your own XAML. Your description doesn't make it very clear to me what your actual visual tree is.

Wpf – Why is the Button’s Background changing

You need to change the Button's Template rather than its Style. Built into the template is something called ButtonChrome, and that is what is causing the irritating blue focus effect. Here is a very simple re-templating of the Button control, taken from the provided Simple Styles:

<Style TargetType="{x:Type Button}">
   <Setter Property="SnapsToDevicePixels" Value="true"/>
   <Setter Property="OverridesDefaultStyle" Value="true"/>
   <Setter Property="MinHeight" Value="23"/>
   <Setter Property="MinWidth" Value="75"/>
   <Setter Property="Template">
     <Setter.Value>
       <ControlTemplate TargetType="{x:Type Button}">
         <Border 
           x:Name="Border"  
           CornerRadius="2" 
           BorderThickness="1"
           Background="#C0C0C0"
           BorderBrush="#404040">
           <ContentPresenter 
             Margin="2"
             HorizontalAlignment="Center"
             VerticalAlignment="Center"
             RecognizesAccessKey="True"/>
         </Border>
         <ControlTemplate.Triggers>
           <Trigger Property="IsKeyboardFocused" Value="true">
             <Setter TargetName="Border" Property="BorderBrush" Value="#202020" />
           </Trigger>
           <Trigger Property="IsDefaulted" Value="true">
             <Setter TargetName="Border" Property="BorderBrush" Value="#202020" />
           </Trigger>
           <Trigger Property="IsMouseOver" Value="true">
             <Setter TargetName="Border" Property="Background" Value="#808080" />
           </Trigger>
           <Trigger Property="IsPressed" Value="true">
             <Setter TargetName="Border" Property="Background" Value="#E0E0E0" />
             <Setter TargetName="Border" Property="BorderBrush" Value="#606060" />
           </Trigger>
           <Trigger Property="IsEnabled" Value="false">
             <Setter TargetName="Border" Property="Background" Value="#EEEEEE" />
             <Setter TargetName="Border" Property="BorderBrush" Value="#AAAAAA" />
             <Setter Property="Foreground" Value="#888888"/>
           </Trigger>
         </ControlTemplate.Triggers>
       </ControlTemplate>
     </Setter.Value>
   </Setter>
 </Style>

You can see that by re-templating the control, you can change its visual tree. The visual tree in this template is nothing more than a Border that contains a ContentPresenter (so you can see the content of the button). I have effectively removed the ButtonChrome from the visual tree this way.

Best Answer

Related Solutions

R – Using WPF, what is the best method to update the background for a custom button control

Wpf – Why is the Button’s Background changing

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