No x:Type, No Problem

I had an interesting problem this week.  I needed to use a default template on a subclassed control.  Ordinarily, that would just be:

Style=”{StaticResource {x:Type BaseClass}}”

Of course in Silverlight, there is no x:Type.

The solution I used was to make an attached behavior that takes the class that has the style, finds the style in the resources and applies it.

The problem

Using a TextBox as an example, here’s some default styling that doesn’t get applied to the subclass:

    <UserControl.Resources>

        <StyleTargetType=“TextBox”>

            <SetterProperty=“Foreground”Value=“Red”/>

        </Style>

    </UserControl.Resources>

    <StackPanel>

        <TextBoxText=“Auto Styled”/>

        <local:TextBoxSubclass/>

It ends up looking like this:

The Solution

With an attached behavior, it can look like this (the bottom TextBoxSubclass has the default TextBox style applied):

    <StackPanel>

        <TextBoxText=“Auto Styled”/>

        <local:TextBoxSubclass/>

        <local:TextBoxSubclass>

            <local:ApplyStyleBehavior.StyleTypeName>

                <TextBox/>

            </local:ApplyStyleBehavior.StyleTypeName>

        </local:TextBoxSubclass>

    </StackPanel>

The attached behavior is pretty simple:

        static void StyleTypeValueChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)

        {

            //need to be loaded so the visual tree can exist and be traversed

            (sender as FrameworkElement).Loaded += (sender1, args) =>

                {

                    (sender as Control).Style = (Style)FindResource(sender, e.NewValue.GetType());

               

                };

        }

        static objectFindResource(DependencyObject start, object resourceKey)

        {

            var nextUp = VisualTreeHelper.GetParent(start);

            while (nextUp != null)

            {

                var fe = nextUp as FrameworkElement;

                if (fe != null)

                {

                    var result = fe.Resources[resourceKey];

                    if (result != null)

                        return result;

                }

                nextUp = VisualTreeHelper.GetParent(nextUp);

            }

            return null;

       

        }

Conclusion

I think its exceedingly obvious how you could apply this universally as a default style on the subclass.  This looks like it has potential to be a pattern to compensate for other Silverlight omissions too.

You can download the full tiny demo on GitHub.