QML Mac fullscreen mode lose mouse focus - macos

Question

I'm using QML to build an OSX application with fullscreen mode support. My intention is to toggle fullscreen/normal mode by double-clicking the main area of the window, here is the minimal code:
import QtQuick 2.4
import QtQuick.Window 2.2
Window {
id: main
visible: true
width: 800; height: 480
flags: Qt.Window | Qt.WindowFullscreenButtonHint // for OSX native behavior support
MouseArea {
anchors.fill: parent
onDoubleClicked: {
if (main.visibility === Window.FullScreen) {
main.visibility = Window.AutomaticVisibility;
} else {
main.visibility = Window.FullScreen;
}
}
}
}
It's very simple, but the behavior is weird:
Whenever the visibility state of the application changes(enter or leave), the user must click in the window one more time before the window mode can change again, just like the application loses the mouse focus.
To validate what I'm thinking, I test something more, I add one more MouseArea(let's say mouseAreaTest) in the window, which split the window side by side and can receive onEntered and onExited event. Right after the application enter or exit fullscreen mode, mouseAreaTest will never receive any Enter or Exit event, unless you click on the window one more time, which is not what I want.
I know nothing about how OSX implement its own fullscreen mode, nor why QML on OSX has such a buggy problem. So I expect someone will tell me something about it.
Update
Later I doubted if this was only something about QML which related something about the Window System of QML, so I tried using traditional QtWidgets, and found the same result there.
Update
I tracked the mouse event of traditional widget, and found the problem: the double click event consisted of two click event(press-release-press-release), when the window state changd(fullscreen to normal or normal to fullscreen), the last RELEASE event will never be received UNLESS click one more time.
I also did more test: use a button to control window state, and the problem is gone, so I may probably consider this is a bug of mouse event handle.
By the way, post system info for a note:
OSX 10.10.1
Qt 5.4.1

Answer 1

This bug still exists in Qt 5.11. I found a workaround eventually.
The reason why the last mouse release event not received is that we toggled fullscreen immediately. Somehow the mouse release event was lost during transition to fullscreen.
So the fix was simple: we postpone toggling fullscreen till next mouse release event. i.e. when we need to toggle fullscreen, set a flag temporarily, then in mouseReleaseEvent, check the flag and do the real work.