Binding to a Control Template

Question

I need to bind a button to a Control Template. The XAML looks something like this:

Button Template="{Binding Status, Converter={StaticResource StatustoTemplate}}"

The converter (StatustoTemplate) runs fine as the status (which is an integer, but happy for it to be a string) changes:

public class StatustoTemplate : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)

        {
           if (value==1)
           {
               return ControlTemplateName1;
           }
           if (value==2)
           {
               return ControlTemplateName2;
           }
        }
}

Now, in what format can I send back ControlTemplate1, or ControlTemplate2? Let us assume that ControlTemplate1 and ControlTemplate2 are valid Control Templates as defined in the XAML. I now that it needs to return a ControlTemplate - but how to set it up?

Answer 1

It is not easy for converter to find resource defined in XAML. I usually define one control template which has both definitions and switch them using Visibility. The code is just a short sample.

XAML

<Window>
    <Window.DataContext>
        <local:MainWindowViewModel/>
    </Window.DataContext>
    <Window.Resources>
        <ResourceDictionary>
            <local:MyConverter x:Key="MyConverter"/>
            <ControlTemplate x:Key="template">
                <Grid>
                    <Grid Visibility="{Binding Status, Converter={StaticResource MyConverter}, ConverterParameter=1}">
                        <TextBox Text="1"/>
                    </Grid>
                    <Grid Visibility="{Binding Status, Converter={StaticResource MyConverter}, ConverterParameter=2}">
                        <TextBox Text="2"/>
                    </Grid>
                </Grid>
            </ControlTemplate>
        </ResourceDictionary>
    </Window.Resources>
    <Grid>
        <Button Template="{StaticResource template}"/>
    </Grid>
</Window>

Converter

public class MyConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return ((string)parameter == "1") ? Visibility.Visible : Visibility.Collapsed;
    }

    // ConvertBack
}

Answer 2

I have a MarkupExtension that might work for you. It is getting xaml defined Resources by ResourceKey.

First: abstract class StyleRefExtension:

public abstract class StyleRefExtension : MarkupExtension
{
    protected static ResourceDictionary RD;
    public string ResourceKey { get; set; }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        return ProvideValue();
    }

    public object ProvideValue()
    {
        if (RD == null)
            throw new Exception(
                @"You should define RD before usage. 
            Please make it in static constructor of extending class!");
        return RD[ResourceKey];
    }
}

Second: class implementation as StyleRefExt

public class StyleRefExt : StyleRefExtension
{
    static StyleRefExt()
    {
        RD = new ResourceDictionary
             {
                 Source = new Uri("pack://application:,,,/##YOUR_ASSEMBLYNAME##;component/Styles/##YOUR_RESOURCE_DICTIONARY_FILE##.xaml")
             };
    }
}

Just replace ##YOUR_ASSEMBLYNAME## with the name of your assembly and ##YOUR_RESOURCE_DICTIONARY_FILE## with the filename of your ResourceDictionary (that is located in folder Styles).

Your Converter should look like this:

public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
    if (value==1) {
        StyleRefExt sr = new StyleRefExt {ResourceKey = "ControlTemplateName1"};
        return sr.ProvideValue();
    }
    if (value==2) {
        StyleRefExt sr = new StyleRefExt {ResourceKey = "ControlTemplateName2"};
        return sr.ProvideValue();
    }
}

Answer 3

my preferred approach is to use a Style with DataTriggers to switch Template, without converters

<Style TargetType="Button" x:Key="StatusButton"> <!--set BasedOn if there is a base Style-->
   <Style.Triggers>
       <DataTrigger Binding="{Binding Status}" Value="1">
           <Setter Property="Template" Value="{StaticResource ControlTemplateName1}"/>
       </DataTrigger>

        <DataTrigger Binding="{Binding Status}" Value="2">
            <Setter Property="Template" Value="{StaticResource ControlTemplateName2}"/>
        </DataTrigger>
    </Style.Triggers>
</Style> 

and then apply this Style:

<Button Style="{StaticResource StatusButton}"/>