Styling a groupbox in WPF

Question

How can I set the opacity of the background for a groupbox etc.

The code beneath doesn't compile:

<Style TargetType="GroupBox">
    <Setter Property="Background">
        <Setter.Value>
            <SolidColorBrush Opacity="0.5">White</SolidColorBrush>
        </Setter.Value>
    </Setter>
</Style>

Answer 1

Your code isn't compiling not because of the opacity, but because of the value "White". You have to apply this to the brush Color.

You can use:

<SolidColorBrush Opacity="0.5" Color="White" />

or

<SolidColorBrush Opacity="0.5">
    <SolidColorBrush.Color>White</SolidColorBrush.Color>
</SolidColorBrush>

Answer 2

you can set the opacity to whatever you want directly on the color. the first two hex numbers control the "alpha" of the brush. 7F is 50%

<SolidColorBrush  x:Key="MyBrush" Color="#7FFFFFFF"/>

so, your style would look like this:

<Style TargetType="GroupBox">
    <Setter Property="Background">
        <Setter.Value>
            <SolidColorBrush Color="#7FFFFFFF"/>
        </Setter.Value>
    </Setter>
</Style>

Answer 3

Opacity is a property of Groupbox itself, not of its background.

Try

<Style TargetType="GroupBox">
    <Setter Property="Background" Value="White"/>
    <Setter Property="Opacity" Value="0.5"/>
</Style>

Or you can style the GroupBox at the place where you use it, as in @Jay's answer.

If you'd really like to change only the background opacity, use the following:

<Style TargetType="GroupBox">
    <Setter Property="Background" Value="#80ffffff"/>
</Style>