CODEWITHSUNDEEP
c#wpfdrag-and-drop
Seth
Seth

Reputation: 8373

How to stop event propagation when dragging and dropping overlapping UI objects in WPF

I have a use case for dragging an item onto an area which could have multiple UI layers.

Use Case 1: Drag and drop a node from a treeview onto a workspace area(drop target). A chart is created in that workspace area.

Use Case 2: Drag and drop a node from a treeview onto a chart, that sits above the original workspace area. Extra data is added to the chart.

The problem with my implementation is that when I conduct Use Case 2, the drop event for the workspace area (Grid) AND chart are called. Not just the one that is visible.

How are others implementing this scenario?

Upvotes: 3

Views: 1551

Answers (2)

Yuriy Zanichkovskyy
Yuriy Zanichkovskyy

Reputation: 1699

To stop routed event propagation set e.Handled = true in drop event handler.

Upvotes: 4

Mario Vernari
Mario Vernari

Reputation: 7304

I would not call your case as "multi-layer". Instead, it is a normal hierarchy of visual objects. For "multi-layer" I mean, for instance, a drop on several sibling canvas.

Anyway, assuming that there is an unique point where the drop-action in managed, I would listen to the drop event (which is bubbling). In the event handler, there is the "OriginalSource" parameter that indicates the very first visual object involved. At this point, you may scan the visual tree upward (VisualTreeHelper), searching for a "chart" element: if you find it, the drop was on a chart, otherwise was on the empty workspace area.

Hope it helps.

Cheers

Upvotes: 1

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