[SOLVED] Local, element-scoped style not applying to children

Local, element-scoped style not applying to children

I'm a WPF beginner and I'm kind of stuck at figuring out why below XAML doesn't do what I believe it should:

<ToolBar HorizontalAlignment="Left" Margin="255,250,0,0" VerticalAlignment="Top">
    <ToolBar.Resources>
        <Style TargetType="{x:Type Separator}">
            <Setter Property="Margin" Value="4,6" />
        </Style>
    </ToolBar.Resources>
    <Button Content="Save"/>
    <Button Content="Cancel"/>
    <Separator />
    <Button Content="Options"/>
</ToolBar>

This should cause the <Separator /> to have the margins of 4,6 but it only does so if I explicitly specify x:Key on the style and the <Separator Style="..." />.

From what I learned so far, my <Style TargetType="{x:Type Separator}"> should apply to all separators inside the <ToolBar>, its child elements, its children's children and so on.

What I'm doing wrong?

Solution

You should set the x:Key to {x:Static ToolBar.SeparatorStyleKey} for the style be applied within a ToolBar:

<ToolBar HorizontalAlignment="Left" Margin="255,250,0,0" VerticalAlignment="Top">
    <ToolBar.Resources>
        <Style x:Key="{x:Static ToolBar.SeparatorStyleKey}" TargetType="{x:Type Separator}">
            <Setter Property="Margin" Value="4,6" />
            <Setter Property="Background" Value="Red" />
        </Style>
    </ToolBar.Resources>
    <Button Content="Save"/>
    <Button Content="Cancel"/>
    <Separator />
    <Button Content="Options"/>
</ToolBar>

This is because the ToolBar class contains some "special" logic for applying default styles to some type of controls including the Separator: https://referencesource.microsoft.com/#PresentationFramework/src/Framework/System/Windows/Controls/ToolBar.cs,5d1684510f45eeb3