How do I go directly from FullScreen to Maximized in a QML Window? - qml

Question

Below is a small QML application. What I intended was for the application to start full screen, and on the Escape key, change it to maximized:
import QtQuick 2.15
import QtQuick.Window 2.15
Window {
id: topLevelWindow
width: 640
height: 480
visible: true
title: qsTr("Hello World")
visibility: Window.FullScreen
Rectangle {
id: rect
anchors.fill: parent
color: "lightBlue"
focus: true
Keys.onPressed: {
if (event.key === Qt.Key_Escape) {
rect.color = "lightGreen"
topLevelWindow.visibility = Window.Maximized
}
}
}
}
What actually happens, though, is that it starts full screen as intended, but pressing Escape makes it windowed but not maximized. Pressing Escape a second time actually maximizes it.
Is there a way to do this without making the user hit Escape twice?

Answer 1

It looks like this is indeed a bug. Seems like it's been lingering for a while, but (some) newer versions may have fixed it?
In the meantime, it's relatively easy to add a hacky workaround:
import QtQuick 2.15
import QtQuick.Window 2.15
Window {
id: topLevelWindow
width: 640
height: 480
visible: true
title: qsTr("Hello World")
visibility: Window.FullScreen
Rectangle {
id: rect
anchors.fill: parent
color: "lightBlue"
focus: true
Keys.onPressed: {
if (event.key === Qt.Key_Escape) {
rect.color = "lightGreen"
topLevelWindow.visibility = Window.Windowed
windowHackTimer.start()
}
}
}
Timer {
id: windowHackTimer
interval: 0
repeat: false
onTriggered: {
topLevelWindow.visibility = Window.Maximized
}
}
}
On the button press it becomes windowed, and then after it returns to the event loop (with a 0ms timer), it sets it to maximized. Just setting topLevelWindow.visibility multiple times in Keys.onPressed doesn't get the job done.

Answer 2

I think you should (1) make sure that the Escape key is accepted by your event handler (so that it is not passed down) and (2) schedule the outcome with Qt.callLater.
Keys.onPressed: {
if (event.key === Qt.Key_Escape) {
event.accepted = true;
Qt.callLater( greenRectAndMaximize );
}
}
function greenRectAndMaximize() {
rect.color = "lightGreen";
topLevelWindow.visibility = Window.Maximized;
}
The event.accept() is important to ensure that no other UI will handle the same event. That could be the cause of your problem. The Qt.callLater is important because it ensures that your action is added to the end of the windows messaging queue so that the UI/UX for the Escape key (and any other UI/UX events can complete) before we do our action.
Generally, whenever processing events, key presses, button clicks, and so forth, think about what needs to happen now and what needs to be queued for later.
In your case, you have a simple action, but, imagine something more complex such as a button click that triggers a page transition and a sort of 10000 records. The UI/UX is the user clicks the button and we want to see the button animate down and up fully before the action kicks off. If we did it during the event handler, the button may appear to be stuck in the down portion of the animation and the app will appear momentarily hang/crash. So, it is important to understand when we need to queue up actions.
Qt.callLater is one of the easiest ways to separate the UI/UX event and the user action and can improve the perceptual responsiveness of your application.