Detect top/parent move event on child widget

gde23

You can use an EventFilter for this:

https://doc.qt.io/qt-5/qobject.html#installEventFilter

Dariusz

@gde23 where do you want me to install it on ? On the child widget?
Installing it on childWidget did not do anything. There are no events popping up as far as I can tell..

mrjj

@Dariusz
Hi
Yes on the child Widgets as an alternative to subclass them all and use moveEvent directly.
https://doc.qt.io/qt-5/qmoveevent.html#details

Are you saying the no such event is posted to the filter when the widgets are moved ?

update:
very fast test

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    ui->frame->installEventFilter(this);
}

bool MainWindow::eventFilter(QObject *watched, QEvent *event)
{

    qDebug() << event->type();

    return QMainWindow::eventFilter(watched, event);
}

void MainWindow::on_pushButton_released()
{

    ui->frame->move(200, 200);
}

Place a Frame on form
Move it with a button
it does report Move event

QEvent::Polish
QEvent::Move
QEvent::Resize
QEvent::Show
QEvent::ShowToParent
QEvent::PolishRequest
QEvent::UpdateLater
QEvent::WindowActivate
QEvent::Paint
QEvent::Paint
QEvent::Enter
QEvent::Leave
QEvent::WindowDeactivate
QEvent::Paint
QEvent::Paint
QEvent::WindowActivate
QEvent::Paint
QEvent::Paint
QEvent::Move <<<<< the actual move via the button
QEvent::Paint
QEvent::WindowDeactivate
QEvent::Hide
QEvent::Hide

Dariusz

@mrjj said in Detect top/parent move event on child widget:

Are you saying the no such event is posted to the filter when the widgets are moved ?

As far as I can tell ye, have a look at this main

   ma = QMainWindow()
    ma.setCentralWidget(parentWidget())

parentWidget.moveEvent() never gets fired.
I don't mind subclassing widgets. But they don't get even moveWindow when I move mainWindow. - ma

Christian Ehrlicher

@Dariusz said in Detect top/parent move event on child widget:

But they don't get even moveWindow when I move mainWindow

Why should the children get a moveWindow event when only the parent moves? The children don't move then (relative) so no event is needed.

Dariusz

@Christian-Ehrlicher Hence my question... How can I properly detect if a "on screen" position of a widget has changed on one of my child widgets?
:- )))

Christian Ehrlicher

You already answered this by yourself - you know when the parent moved, so the absolute position of the child must have changed too...

mrjj

Hi
Ahh. now i get what you ask. The reverse.
But why would you need to know that?
the children will move with parents automatically.

Dariusz

@mrjj I have created a "new" floating widget. That user can move anywhere to screenn, but at the same time widget will move in relation to specified X widget. For example it will be a button in future. Now when button moves that can be a child of Widget>dockWidget>mainWindow changing position of mainWindow, will move button to new position thus my hover widget has to move as well. Same goes if user change dockWidget position... and there can be nested hierarchy like docket>docked>docked/etc/etc... so I'm looking if there is any way at all to be notified if a widget change its screen position at any time...

The example above shows that. where self.w is my floating widget that is meant to follow parentWidget... but when parent widget is a centralWidget of mainWindow... then the self.w no longer gets notified to change its positionw hen parentWIdget gets moved via its parent...

Dariusz

@Christian-Ehrlicher said in Detect top/parent move event on child widget:

You already answered this by yourself - you know when the parent moved, so the absolute position of the child must have changed too...

I'm not sure... as far as I can tell I have to recrusively notify all widgets children+their children+their children of position/size/ change and let them all recalculate properly.... but I'm not sure if thats the best approach...

mrjj

@Dariusz said in Detect top/parent move event on child widget:

as far as I can tell I have to recrusively notify all widgets children+their children+their children of position/size/ change and let them all recalculate properly

That's what Layouts normally are for. Automatic resize when parent is resized.

Did you use layouts for the children ?

Dariusz

@mrjj Yes I did, so I take I could listen to layout resizeevent/etc. But what about moveEvent?

Christian Ehrlicher

@Dariusz said in Detect top/parent move event on child widget:

But what about moveEvent?

Again: they do not move - so there is no move event!

Dariusz

@Christian-Ehrlicher So how can I detect it? Or I have to travers entire hierarchy ?

Christian Ehrlicher

This was already answered.

mrjj

@Dariusz said in Detect top/parent move event on child widget:

@mrjj Yes I did, so I take I could listen to layout resizeevent/etc. But what about moveEvent?

well, you can add a new signal to the top parent and then hook up that signal
to all children. then in
parent moveEvent emit the signal to tell the children

But i cannot for the life of me understand why you need that.
If using layouts, the child will scale with Parent and a child is
NOT moved when a parent is moved. it stays in same position inside the parent. So no need for it to know it at all.

Dariusz

@mrjj Did you look at the example above? The childWidget is not actually in layout or anything like that... he does not even have parent. Hes being moved by parentWidget() inside moveEvent... I'm trying to affect non-related widget... MoveEvent() moves its correctly... except that it does not when the parentWidget is inside another widget... So I'm trying to get that example code above work. Without having to recursively spam hundreds of widgets... Perhaps I should not name them childWidget/parentWidget :/

Dariusz

@Christian-Ehrlicher said in Detect top/parent move event on child widget:

This was already answered.

Are you reffering to this?

@Christian-Ehrlicher said in Detect top/parent move event on child widget:

You already answered this by yourself - you know when the parent moved, so the absolute position of the child must have changed too...

What signal/slot/function does get called on child to notify it of new parent position ?

kshegunov

@Dariusz said in Detect top/parent move event on child widget:

What signal/slot/function does get called on child to notify it of new parent position ?

None. If a widget is moved in relation to its parent's client rect (for top-level windows the "parent's client rect" is the screen), then it's going to receive a move event. Listen to that event, if you wish, by means of installing an event filter, as already mentioned.

There's no signal/slot/function that gets called on the children to notify of move, because that makes no sense. The parent moves, hence the rect of the widget (the non-client rect) moves, but children's rects are still left exactly the same relative to their parent's rect, so they ain't moving, hence no move event.

mrjj

@Dariusz
Ahhhhhhhhhhh. We are talking floating widgets here :)
That explains a lot.

When you say "child" it implies it has a parent that Widget acting as a window
never has. (QDialog types being an exception)

So you on the right way with moveEvent and some signal.

except that it does not when the parentWidget is inside another widget.
Which would make it a child. :) but in this case, it will move with the parent automatically.

In any case, you should be aware of
QApplication::topLevelWidgets()

that will give a list with all Windows types. those are the one, you want to move manually.