How to prevent InvokeCommandAction from propagating event to parent elements?

问题

I realised that when using an InvokeCommandAcction associated to an EventTrigger, the original event was still routing up to the parent elements until it is handled. Well, I guess it is an expected behavior. But my question is how I can mark the event as Handled so it does not propagate up through the whole UI tree?

Actually, as you handle this event in a command, everything will be handled in this command, therefore it does not need to propagate. And in one corner case I found, it causes some unwanted behavior. For example, I open a new window when a user double click an element (MouseDoubleClick event). The problem is that the new windows opens and then the main window come back in front of the new one because the MouseDoubleClick event just reached the top element in the UI tree. The wanted behavior would be to keep the new window in front, but as the InvokeCommandAction lets the event propagate up, the main window takes back the focus...

What I could do is to use the CallMethodAction asset instead but as I am in a MVVM scenario, I don't want UI event arguments in my code. Even if this would let me implicitely mark the event as handled and fix the issue.

<UserControl x:Class="..."
             xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity">
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="MouseDoubleClick">
            <i:InvokeCommandAction Command="{Binding Path=DisplayReportCommand}"/>
        </i:EventTrigger>
    </i:Interaction.Triggers>
    ...
</UserControl>

回答1:

You could implement your own EventTrigger that marks events as handled.

public class HandlingEventTrigger : System.Windows.Interactivity.EventTrigger
{
    protected override void OnEvent(System.EventArgs eventArgs)
    {
        var routedEventArgs = eventArgs as RoutedEventArgs;
        if (routedEventArgs != null)
            routedEventArgs.Handled = true;

        base.OnEvent(eventArgs);
    }
}

Then replace <i:EventTrigger EventName="MouseDoubleClick"> with <local:HandlingEventTrigger EventName="MouseDoubleClick"> and add

xmlns:local="clr-namespace:HandlingEventTrigger's namespace here"

to your usercontrol's atributes.

回答2:

Add attached event to user control

              CommandManager.PreviewCanExecute="PreviewCanExecute"

and in event handler

               e.ContinueRouting = false;

Hope this will help!

回答3:

MouseDoubleClick Event is actually not a bubbling routed event but a direct routed event.

However, this event is raised along the element tree, which can be checked with Snoop tool. Moreover, even if Handled for MouseDoubleClick is set to true, this event will occur along the element tree.

Although this routed event(MouseDoubleClick Event) seems to follow a bubbling route through an element tree, it actually is a direct routed event that is raised along the element tree by each UIElement.

If you set the Handled property to true in a MouseDoubleClick event handler, subsequent MouseDoubleClick events along the route will occur with Handled set to false. This is a higher-level event for control consumers who want to be notified when the user double-clicks the control and to handle the event in an application. (From MSDN)

As above, your problem may be not caused by the propagating as you mentioned. There is Window.ShowActivated property, which determines whether a window is activated when first shown. You can set the property in a sub window(xaml) as below but please note that though ShowActivated can give the focus to the main window, it cannot let the main window visually keep in front of the sub window. I have tried to find the solution but have no idea until now.

<Window ShowActivated="False" ....>
....
</Window>

来源：https://stackoverflow.com/questions/7647625/how-to-prevent-invokecommandaction-from-propagating-event-to-parent-elements

标签

wpf

mvvm

command

invoke-command

event-routing