How can I efficiently apply the same WPF behavior to multiple controls using styles and custom attached properties?

Extend styles with mixed behaviors in WPF

In WPF, adding functionality to controls is usually achieved by defining behaviors. However, applying the same behavior to multiple instances using inline XAML can be difficult due to limitations in accessing attached properties. This problem can be overcome by using a combination of custom attached properties and extended behavior collection classes.

The main hurdle is the lack of accessible setters for behavior and trigger attached properties, as well as the internal constructor of the base behavior class. To solve these problems, we introduced our own behavior and trigger collection classes.

Additionally, to ensure that behaviors and triggers are additive rather than replacing existing behaviors and triggers, we leverage custom attached properties to interact with the main behavior and trigger properties. The x:Shared attribute ensures that a new copy is created each time the style target resource is referenced, ensuring that multiple elements can benefit from the behavior without conflicting.

Example implementation

The following example demonstrates the application of extending behavior through styles:

<Grid>
    <Grid.Resources>
        <String x:Key="stringResource1">stringResource1</String>
        <local:Triggers x:Key="debugTriggers" x:Shared="False">
            <local:EventTrigger EventName="MouseLeftButtonDown">
                <local:DebugAction Message="DataContext: {0}" MessageParameter="{Binding}" />
                <local:DebugAction Message="ElementName: {0}" MessageParameter="{Binding Text, ElementName=textBlock2}" />
                <local:DebugAction Message="Mentor: {0}" MessageParameter="{Binding Text, RelativeSource={RelativeSource AncestorType={x:Type FrameworkElement}}}" />
            </local:EventTrigger>
        </local:Triggers>
        <Style x:Key="debugBehavior" TargetType="{x:Type TextBlock}">
            <Setter Property="local:SupplementaryInteraction.Triggers" Value="{StaticResource debugTriggers}" />
        </Style>
    </Grid.Resources>
    <StackPanel DataContext="{StaticResource stringResource1}">
        <TextBlock Name="textBlock1" Style="{StaticResource debugBehavior}" Text="textBlock1" />
        <TextBlock Name="textBlock2" Style="{StaticResource debugBehavior}" Text="textBlock2" />
        <TextBlock Name="textBlock3" Style="{StaticResource debugBehavior}" Text="textBlock3" />
    </StackPanel>
</Grid>

This example demonstrates various scenarios such as data binding within an action by leveraging behavior through triggers.

Custom behaviors and collections

Part of the extended behavior implementation, DebugActionBehavior:

public class DebugAction : TriggerAction<DependencyObject>
{
    public string Message { get; set; }
    public object MessageParameter { get; set; }

    protected override void Invoke(object parameter)
    {
        Debug.WriteLine(Message, MessageParameter, AssociatedObject, parameter);
    }
}

Behavior collection class:

public class Behaviors : List<Behavior> { }
public class Triggers : List<TriggerBase> { }

Customized additional attributes

Additional properties for interacting with the main behavior and trigger properties:

public static class SupplementaryInteraction
{
    public static void SetBehaviors(DependencyObject obj, Behaviors value) { obj.SetValue(BehaviorsProperty, value); }
    public static void SetTriggers(DependencyObject obj, Triggers value) { obj.SetValue(TriggersProperty, value); }

    public static readonly DependencyProperty BehaviorsProperty = DependencyProperty.RegisterAttached("Behaviors", ...);
    public static readonly DependencyProperty TriggersProperty = DependencyProperty.RegisterAttached("Triggers", ...);
}

By taking this approach, developers can seamlessly apply complex behaviors to multiple elements through styles, thereby increasing the flexibility and maintainability of WPF applications.

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