CODEWITHSUNDEEP
c#xamlsilverlight
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Reputation: 955

Silverlight slider control does not trigger mouseleftbuttondown event

I have a slider like below:

<Slider Minimum="0" Maximum="{Binding TotalNumberOfPositions,Mode=TwoWay}" Value="{Binding CurrentPosition, Mode=TwoWay}" Margin="5" >
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="MouseLeftButtonUp" >
            <i:InvokeCommandAction Command="{Binding StopSeekPosition, Source={StaticResource ViewModel}}" />
        </i:EventTrigger>
        <i:EventTrigger EventName="MouseLeftButtonDown">
            <i:InvokeCommandAction Command="{Binding StartSeekPosition, Source={StaticResource ViewModel}}" />
        </i:EventTrigger>
    </i:Interaction.Triggers>
</Slider>

The MouseLeftButtonUp event is working well and command will be triggered. However MouseLeftButtonDown is not triggered or it does not trigger my StartSeekPostion command. I have checked command names in MVVM. Everything is normal but it does not work. I really stuck on this. Is it something wrong with my code or is it an issue about slider control?

Upvotes: 0

Views: 103

Answers (1)

Martin
Martin

Reputation: 6136

Neither is anything really wrong with your code nor is this an issue of the Slider, but when dealing with RoutedEvents you always have to keep in mind that anywhere along the route some eventHandling code can handle the event (and if further down the tree: before your handler had the chance), mark it as handled, and your handler will not be called.

So, most likely, the Slider control has a handler for MouseLeftButtonDown that sets eventArgs.Handled = true;

But you can prepare for this: use the method UIElement.AddHandler( routedEvent, handler, handledEventsToo), either call it in your code-behind and wire up the event and eventHandler there, or write your own trigger (like <MouseLeftButtonDownEventTrigger HandledEventsToo="true">) with a flag HandledEventsToo.

Code-Behind

mySlider.AddHandler(UIElement.MouseLeftButtonDownEvent,
    new MouseButtonEventHandler( HandleMouseLeftButtonDown ), handledEventsToo: true);
...
private void HandleMouseLeftButtonDown( object sender, MouseButtonEventArgs e ){...}

custom trigger

public class MouseLeftButtonDownEventTrigger : TriggerBase<UIElement>
{
    public bool HandledEventsToo { get; set; }

    public bool MarkHandled { get; set; }

    private readonly MouseButtonEventHandler m_buttonDownHandler;

    public MouseLeftButtonDownEventTrigger()
    {
        m_buttonDownHandler = Invoke;
    }

    private void Invoke( object sender, MouseButtonEventArgs eventArgs )
    {
        InvokeActions( null );
        if (MarkHandled) eventArgs.Handled = true;
    }

    protected override void OnAttached()
    {
        base.OnAttached();
        AssociatedObject.AddHandler( UIElement.MouseLeftButtonDownEvent,
            m_buttonDownHandler, HandledEventsToo );
    }

    protected override void OnDetaching()
    {
        AssociatedObject.RemoveHandler( UIElement.MouseLeftButtonDownEvent,
            m_buttonDownHandler );
        base.OnDetaching();
    }
}

Upvotes: 1

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