fix(windows): keep a drag alive when the cursor leaves the view - #11
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MouseRegion.onExit forwarded LEAVE unconditionally, including while a mouse button was still held. WebView2 turns that into WM_MOUSELEAVE and Chromium ends the gesture in flight, so dragging past the edge of the view -- how a selection is extended on every platform -- drops the selection the user is making. Flutter keeps routing those drag moves to this view until the button comes up, so the pointer has not actually gone anywhere as far as the gesture is concerned. Withhold the LEAVE while any button is down and deliver it on button-up or cancellation; swallow the matching ENTER when the cursor comes back first, so the native hover state stays paired. WebView2 has no mouse-cancel event. Translate Flutter cancellation to the matching button-up before delivering the deferred LEAVE, which clears the native button state. Leave arguments remain zero as required by WebView2 SendMouseInput.
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The bug
On Windows, dragging the mouse out of the WebView while a button is held ends the gesture. This breaks text-selection extension, drag-and-drop, and mousemove-driven UI.
Root cause
MouseRegion.onExitfires when the cursor crosses the widget bounds, including mid-drag. Flutter continues routing the captured pointer sequence to theListener, but forwarding that exit as WebView2LEAVEmakes Chromium end the in-flight gesture.Fix
LEAVEwhile any mouse button is down, then send it after the final button-up or cancellation.The implementation deliberately leaves the WebView2
LEAVEarguments at zero, as required by itsSendMouseInputcontract.Tests
custom_platform_view_drag_test.dartcovers dragging out, forwarding out-of-bounds cursor positions, releasing/cancelling outside, re-entry during a drag, right-button drags, and ordinary hover behavior.Validation after rebasing onto current
master:flutter analyzeflutter test(44 tests)