[Linux] [KDE Plasma] onDragEntered and onDragUpdated triggered when user come back from another window

[sun-jiao]

A clear and concise description of what the bug is.

Reproduce Steps

Steps to reproduce the behavior:

1. Click another window
2. Move the cursor back to flutter app
3. Click the DropTarget
4. onDragEntered or onDragUpdated is triggered.

Expected behavior

A single click should not trigger anything.

Version (please complete the following information):

• Flutter Version: 3.19.4
• OS: Linux
• plugin: desktop_drop: 0.4.4

desktop_drop_example.mp4

[sun-jiao]

Tested on the example of master branch.

No matter which one is clicked, callbacks are only triggered in the just last used one.

[sun-jiao]

Seems this is a GTK or KDE bug: https://gitlab.gnome.org/GNOME/gtk/-/issues/5519 https://bugs.kde.org/show_bug.cgi?id=464196

While I think there still be some workaround in this flutter plugin, for example: clear previous _offset on the "focus-in-event" signal, and do not call _notifyEvent on the following first "drag-motion" signal.

Of course, this will lead to an obvious side effect. When the cursor just enters DropTarget, UI will not change. Only when the cursor moves slightly within DropTarget, UI will be updated.

However, manual operations by human could trigger drag-motion very frequently, and I think the latency of UI update is almost imperceptible to human users. And for users performing bulk actions using automated mouse emulators, UI updates is not important.