Question

Problem

I’ve created a custom control (OmniBox), which has its base style set with:

<Style x:Key="GridStyle" TargetType="Grid" BasedOn="{StaticResource BaseElement}">
    <Setter Property="Margin" Value="0,2" />
</Style>

But when I’m using my control, I want to be able to do something like:

<UserControl.Resources>
    <Style TargetType="{x:Type ui:OmniBox}">
        <Setter Property="HorizontalAlignment" Value="Stretch"/>
        <Setter Property="Margin" Value="0,10"/> <!--Not Working?-->
    </Style>
</UserControl.Resources>
<Grid>
     <StackPanel>
           <ui:OmniBox x:Name="One"... />
           <ui:OmniBox x:Name="Two"... />
           ...

And have all instances of my control take on that default margin. Unfortunately, my controls are not responding to the style set in the resources. They are just keeping their default margin of “0,2”.

Strangely, if I explicitly set the margin on my controls like so:

           <ui:OmniBox x:Name="One" Margin="0,10" Style="OBDefaultStyle" ... />
           <ui:OmniBox x:Name="Two" Margin="0,10" ... />
           ...

They DO use the margin of “0,10” rather than “0,2”. How come the template type isn’t working?

If it’s relevant, my OmniBox control templates all look like this:

<Style TargetType="{x:Type local:OmniBox}" x:Key="OBDefaultStyle">
    <Setter Property="Template" Value="{StaticResource OBDefaultTemplate}" />
</Style>
<ControlTemplate TargetType="{x:Type local:OmniBox}" x:Key="OBDefaultTemplate">
    <Grid x:Name="PART_Grid" Style="{StaticResource GridStyle}">
        ... (Content)
    </Grid>
</ControlTemplate>

---

First Attempt

In my grid style, I’ve tried setting Margin to

<Setter Property="Margin" 
        Value="{Binding Path=Margin, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:OmniBox}}}" />

But it didn’t help in sucking down the templated margin.

Second Attempt

I tried creating a custom margin dependency property and binding the grid to that:

<Style x:Key="GridStyle" TargetType="Grid" BasedOn="{StaticResource BaseElement}">
    <Setter Property="Margin" Value="{Binding Path=MyMargin, RelativeSource={RelativeSource TemplatedParent}}" />
</Style>

My custom property was defined as:

public static readonly DependencyProperty MarginProperty = DependencyProperty.Register("Margin", typeof(Thickness), typeof(OmniBox), new FrameworkPropertyMetadata(new Thickness(0,2,0,2), new PropertyChangedCallback(OnMarginChanged)));

Anyways it didn’t work. The default margin set in the dependency property above is still overriding the margin I’m trying to set in the style template.

Answer 1

After happening on this question, I figured out what I needed to do. In the control’s class, I need to override the margin property’s default value:

    static OmniBox()
    {
        MarginProperty.OverrideMetadata(typeof(OmniBox), new FrameworkPropertyMetadata(new Thickness(0,2,0,2)));
    }

After that, I get rid of the margin on the “Grid” component of the omnibox completely, since the control itself carries a margin. Now when the user sets the “Margin” property on the OmniBox, it accepts it, if they don’t, it uses the default value.

Thank you all so much for your suggestions and effort.