CODEWITHSUNDEEP
wpf
Cobold
Cobold

Reputation: 2613

Disable event bubbling

I have this style:

        <Style TargetType="{x:Type Expander}">
            <Setter Property="BorderBrush" Value="LightGray"/>
            <Setter Property="Margin" Value="5"/>

            <EventSetter Event="Mouse.MouseEnter" Handler="ExpanderMouseEnter"/>
            <EventSetter Event="Mouse.MouseLeave" Handler="ExpanderMouseLeave"/>
        </Style>

When I add an expander as a child to an expander and mouseover the child expander, both of the expanders gets colored gray. How can I set the e.handled = true to the event to stop it from bubbling up?

EDIT: OK so I had to edit the style to call a code-behind method. Here are the methods: 

Private Sub ExpanderMouseEnter(ByVal sender As Expander, ByVal e As MouseEventArgs)
        sender.Background = Brushes.LightGray
        e.Handled = True
    End Sub

    Private Sub ExpanderMouseLeave(ByVal sender As Expander, ByVal e As MouseEventArgs)
        sender.Background = Brushes.White
        e.Handled = True
    End Sub

But nothing changes. What's the problem?

Upvotes: 2

Views: 1255

Answers (3)

Vinit Sankhe
Vinit Sankhe

Reputation: 19885

Ideally writing a Trigger to change the background with IsMouseDirectlyOver flag should work as this flag is intended for UIElements to activate triggers ONLY on which mouse is directly over.

But it seems to fail for expanders because inner expander is part of outer expander's visual tree.

I believe what you might consider is to have IsMouseOver trigger on the Header element of expanders. They are mutually exclusive of each other's visual tree. So when you mouse over the headers the expanders will get their characteristic background color.

Upvotes: 2

RandomActsOfCode
RandomActsOfCode

Reputation: 3285

I think the real problem is that a MouseLeave event is not fired when the mouse moves from the outer expander into the inner expander. As a result, the IsMouseOver property used in your Triggers remains set on both (as in your original question). So even if you could set the Handled property to True as the mouse enters the second expander, your Trigger would still be active on the outer control, and the background set.

Upvotes: 0

Jon
Jon

Reputation: 437336

It looks like this is not possible using no code-behind, because neither Trigger nor EventTrigger (which you could use alternatively in this scenario) expose any relevant functionality.

Unless you can work around the issue (e.g. by only applying the style, or parts of it, to descendant expanders), you will have to implement an event handler in code-behind and set the Handled property from there.

Upvotes: 0

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