How to get the target window of QTouchEvent

Wei Wei

In qt5 there is a QTouchEvent::window() method to get which QWindow this touch event will be sent to, in Qt6 this interface has been removed, what can I do to replace it?

I've tried using this way:

QObject* target = te->target();
QWindow* targetWindow;
    if (target->isWindowType())
        targetWindow = dynamic_cast<QWindow*>(target);
    else {
        WId wid = static_cast<QWidget*>(target)->winId();
        targetWindow = QWindow::fromWinId(wid);
    }

but I've found that the result isn't entirely accurate, and the first time I receive QTouchEvent, I get an error QWindow instead of the QWidgetWindow I expected

jsulm

@Wei-Wei You can use https://doc.qt.io/qt-6/qtouchevent.html#target and then check whether you can cast it to QWidget* if you can use https://doc.qt.io/qt-6/qwidget.html#window

Wei Wei

@jsulm The return of https://doc.qt.io/qt-6/qwidget.html#window is a QWidget*, but i need a QWindow*

I find i can get the right window like this:

// target is a QObject* such as a event receiver
QWidget* targetWidget = static_cast<QWidget*>(target);
targetWindow = targetWidget->window()->windowHandle();

sierdzio

Just a side-note to casting: in Qt world you can use qobject_cast<>(), it's as fast as static cast but as flexible as dynamic cast. Works only on subclasses of QObject.

Wei Wei

@sierdzio got it, thank you

jsulm

@Wei-Wei said in How to get the target window of QTouchEvent:

is a QWidget*, but i need a QWindow*

Please read again what I wrote...

Wei Wei

@jsulm emmm，like this？

if (event->target()->isWidgetType()) {
    QWidget* targetWidget = qobject_cast<QWidget*>(event->target());
    QWidget* window = targetWidget->window();
}

jsulm

@Wei-Wei Yes, but you also should always check pointers after casting. Casting can fail you then end up dereferencing an invalid pointer...

Wei Wei

@jsulm After I checked that isWidgetType() is true, cast can still fail? Is a bug of Qt?

And thank you for the ideas, i find "QMutableEventPoint::window(const QEventPoint &)" that solved my problem.

JonB

@Wei-Wei said in How to get the target window of QTouchEvent:

@jsulm After I checked that isWidgetType() is true, cast can still fail? Is a bug of Qt?

Maybe, maybe not, But for the sake of an extra statement you should always check the return result of a qobject_cast<>() or a dynamic_cast<>() as a matter of course. Q_ASSERT(targetWidget); would suffice if you're sure it should be true.

Wei Wei

@JonB Check the return result of a qobject_cast<>() or a dynamic_cast<>() is a good habit, i will remember it.

Wei Wei

I found QMutableEventPoint::window(const QEventPoint &) can solve my problem.