如何在 Silverlight XAML 中引用另一个名称空间中的绑定转换器？

Question

Since you apparently can't create a Silverlight DataTemplate in C#, I'm trying to create one in XAML. I have a converter that I need to refer to, that I have defined in C# in another namespace. I've tried doing this:

<UserControl.Resources>
        <DataTemplate x:Key="PriceTemplate">
            <TextBlock Text="{Binding Price, Converter={Converters:PriceConverter}}" />
        </DataTemplate>
    </UserControl.Resources>

Where Converters is an xmlns that points to the correct namespace. However, I get a compilation error that says:

Type 'Converters:PriceConverter' is used like a markup extension but does not derive from MarkupExtension.

I tried adding System.Windows.Markup.MarkupExtension as a parent to my converter, but it apparently doesn't exist in Silverlight.

How can I refer to my converter in XAML, without having to rewrite it in XAML?

Answer 1

You want to make a static resource first, then bind to the converter that is a static resource.

 <UserControl.Resources> 
   <conv:IntConverter x:Key="IntConverter"></conv:IntConverter> 
 </UserControl.Resources> 
 <StackPanel> 
    <TextBlock x:Name="Result" Margin="15" FontSize="20" 
              HorizontalAlignment="Center" VerticalAlignment="Center" 
               Text="{Binding Converter={StaticResource IntConverter}}"> 
    </TextBlock> 
 </StackPanel> 
</Window>

So the "conv:" xml namespace was registered at the top of the document like you do with custom controls:

xmlns:conv="clr-namespace:MyFooCompany.Converters"

This example is adapted from the below linked tutorial regarding the same issue for WPF:

http://www.dev102.com/2008/07/17/wpf-binding-converter-best-practices/

Answer 2

You seem to be confusing Types with Instances. A converter type will exist "in" a namespace however in binding we do not specify a type as the converter. Instead we give the binding an actual instance of that type.

Generally IValueConverter instances are stateless, hence we can hold a common instance anywhere in a the chain of resource dictionaries available where the instance of a DataTemplate is loaded.

In xaml we can reference another namespace by creating a new alias to cover it. With that in mind your xaml could look something like this:-

<UserControl x:Class="SilverlightApplication1.UserControl1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:SilverlightApplication1"
    xmlns:localConverters="clr-namespace:SilverlightApplication1.Converters">
    <UserControl.Resources>
        <localConverters:PriceConverter x:Key="PriceConverter" />
        <DataTemplate x:Key="Test">
            <TextBlock Text="{Binding Price, Converter={StaticResource PriceConverter}}" />
        </DataTemplate>
    </UserControl.Resources>

Answer 3

<RadioButton GroupName="Group1">
    <RadioButton.Template>
        <ControlTemplate>
            <ToggleButton IsChecked="{Binding IsChecked, RelativeSource={RelativeSource TemplatedParent}, Mode=TwoWay}">
                <ToggleButton.Content>
                    <SymbolIcon Symbol="Edit"/>
                </ToggleButton.Content>
                <ToolTipService.ToolTip>
                    <ToolTip Content="Sample Tooltip" Placement="Mouse" />
                </ToolTipService.ToolTip>
            </ToggleButton>
        </ControlTemplate>
    </RadioButton.Template>
</RadioButton>

Adding to the answer posted by @Rokk.

Answer 4

In addition to the other answers suggesting creating an instance of the ValueConverter in a resource dictionary, another solution is to implement it via a MarkupExtention:

public class IntToLetterConverter : IMarkupExtension<IValueConverter>, IValueConverter
{
    public IValueConverter ProvideValue(IServiceProvider serviceProvider)
        => (IValueConverter)this;

    object IMarkupExtension.ProvideValue(IServiceProvider serviceProvider)
        => ((IMarkupExtension<IValueConverter>)this).ProvideValue(serviceProvider);

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        => (char)('a' + (int)value);

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        => (int)((char)value - 'a');
}

With this solution you can directly reference the converter (which is in essence a MarkupExtension) whithout defining a resource.