Propagate an attached dependency property value to a template

Question

Can an attached dependency property value be propagated to a templated children ?

Example : trying to propagate TagCloudService.* properties to the ItemTemplate

<ItemsControl x:Name="myItemsControl"
                pages:TagCloudService.MaximumFontSize="20"
                pages:TagCloudService.MaximumFontWeight="800"
                pages:TagCloudService.MinimumFontSize="10"
                pages:TagCloudService.MinimumFontWeight="400"
                pages:TagCloudService.NumberOfSizes="5"
                pages:TagCloudService.TagFrequency="{Binding Hotttnesss}"
                pages:TagCloudService.TagWeight="{Binding Weight}"
                Template="{StaticResource TagCloudItemsControlTemplate}">
    <ItemsControl.ItemTemplate>
        <StaticResource ResourceKey="TermTagCloudTemplate" />
    </ItemsControl.ItemTemplate>
</ItemsControl>

Here is the item template where some default values have been defined but should be overridden :

<DataTemplate x:Key="TermTagCloudTemplate" DataType="api:Term">
        <TextBlock Foreground="DodgerBlue"
                    Padding="10"
                    Style="{StaticResource TagCloudTextBlockStyle}"
                    Text="{Binding Name}"
                    pages:TagCloudService.MaximumFontSize="30"
                    pages:TagCloudService.MaximumFontWeight="800"
                    pages:TagCloudService.MinimumFontSize="20"
                    pages:TagCloudService.MinimumFontWeight="400"
                    pages:TagCloudService.NumberOfSizes="5"
                    pages:TagCloudService.TagFrequency="{Binding Frequency}"
                    pages:TagCloudService.TagWeight="{Binding Weight}">
        </TextBlock>
</DataTemplate>

I've tried to set FrameworkPropertyMetadataOptions.OverridesInheritanceBehavior instead of .Inherits, tried to comment the default values in the template but the properties are not propagated.

Is this possible or should I just create another ItemTemplate for that control ?

Answer 1

It's actually easy.

Declare the attached property with Inherits-option:

public static string GetFoo(DependencyObject obj)
{
    return (string)obj.GetValue(FooProperty);
}

public static void SetFoo(DependencyObject obj, string value)
{
    obj.SetValue(FooProperty, value);
}

public static readonly DependencyProperty FooProperty =
    DependencyProperty.RegisterAttached(
        "Foo", typeof(string), typeof(MainWindow),
        new FrameworkPropertyMetadata(
               "default",
               // this bit is important:
               FrameworkPropertyMetadataOptions.Inherits));

Test XAML:

<Grid src:MainWindow.Foo="non-default">
    <TextBlock Text="{Binding (src:MainWindow.Foo),
                              RelativeSource={RelativeSource Self}}"/>
</Grid>

shows "nondefault".

This works across template boundary as well, full example follows.

<Window x:Class="DPInheritance.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:src="clr-namespace:DPInheritance"
        xmlns:sys="clr-namespace:System;assembly=mscorlib"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <DataTemplate x:Key="Test">
            <TextBlock Text="{Binding (src:MainWindow.Foo),
                                      RelativeSource={RelativeSource Self}}"/>
        </DataTemplate>
    </Window.Resources>
    <Grid src:MainWindow.Foo="non-default">
        <ItemsControl ItemTemplate="{StaticResource Test}">
            <sys:Int32>0</sys:Int32>
            <sys:Int32>1</sys:Int32>
            <sys:Int32>2</sys:Int32>
        </ItemsControl>
    </Grid>
</Window>