QML orientation observer

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In one of my mobile QML applications, I need to know when the handset orientation changes. The runtime knows but it doesn't offer a signal to my code. Here is a QML hack that observes when orientation changes. It watches both height and width for changes. When they have both changed, it sets a boolean property to 'true'. This works on handsets because both height and width change when orientation changes. It probably won't work on a desktop because there it's easy to change one without the other.

/*
 Hack to observe changes in orientation from portrait to landscape in a Rectangle.

Observation: On handsets, both the width and the height of the
 Rectangle will change when orientation changes. There is no way to
 catch both changes at the same time, so we catch them individually
 and set corresponding bools so we can remember the events. When we
 observe that both flags are 'true', we determine the orientation
 and set both bools back to 'false'.
*/
property bool changeOfWidth: false
property bool changeOfHeight: false
property bool newOrientation: false

onWidthChanged: {changeOfWidth = true; newOrientation = (changeOfWidth && changeOfHeight)}
onHeightChanged: {changeOfHeight = true; newOrientation = (changeOfWidth && changeOfHeight)}

onNewOrientationChanged: {
 if (newOrientation) {
 changeOfWidth = false;
 changeOfHeight = false;

if (width > height) {
 // landscape
 console.log("landscape")
 } else {
 // portrait
 console.log("portrait")
 }
 }
}

For Qt 5.2 and greater:

import QtQuick.Window 2.2

then in your code:

property bool isPortrait: Screen.primaryOrientation === Qt.PortraitOrientation || Screen.primaryOrientation === Qt.InvertedPortraitOrientation

onIsPortraitChanged: console.log("isPortrait", isPortrait)

The Screen object does not provide signals for when it's members change directly, but you can create your own via binding to the Screen object's properties.

This binding will be fired after the height and width changes are completed, so it's safe to recalculate your metrics or animations based on the new properties at this time.