Detect top/parent move event on child widget

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.

Dariusz

@mrjj Yes I have totally failed. I should have not called it parent/child as it confused every1 and no1 has read the code :- )))

So I'll try to rephrase the question here...

Problem A:
I have 2 widgets.
WidgetA is a data widget, say QGraphicsView. - this widget can be inside layout of another widget.
WidgetB is a floating window, with tools.

The idea is that whenever WidgetA moves, the widgetB should move with it - as well as being able to move by itself - it's all in the python example above...

The problem is, that if WidgetA is inside layout, then it no longer informs widgetB of the new position because it don't get move events.

Current working "approach" that I can think off is that I have to subclass all of my widgets, and reimplement their moveEvent() & inform each child widget of new position so that they can properly handle their positioning in relationship to new parent position.

On another side I'm also thinking of implementing a qApp->eventFilter() - a global one, then look for moveEvent() in there and emit signals to all registered widgets from that...

Given that my app is "dynamically" build, meaning that parenting/widget hierarchy can change at any time, I'm looking for "automated" approach, hard coding stuff won't work here :- )

Problem B: (just emerged)
How do I et WidgetB Z depth, to be always +1 over its WidgetA so that it can be always visible above WidgetA but not visible if WidgetX moves mover it... ?

TIA :- )

mrjj

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

Oh yes. Words can be deceiving. I did read the code but since you said child widget i still
didnt get why you needed any code at all :)

The problem is, that if WidgetA is inside layout, then it no longer informs widgetB of the new position because it don't get move events.

But why must it be WidgetA ? should dit not be the top widget (the window) ?
Or the issue is that sometimes
WidgetA is a window and life is good, but then same class (WidgetA ) is used in a layout and then suddenly
it cant inform widgetB any more since only top parent knows it was moved ?

Something like that ?

Dariusz

I'm sorry, my bad :- ((

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

@Dariusz said in Detect top/parent move event on child widget:
Or the issue is that sometimes
WidgetA is a window and life is good, but then same class (WidgetA ) is used in a layout and then suddenly
it cant inform widgetB any more since only top parent knows it was moved ?
Something like that ?

Yes, since its dynamically generated UI based on a user template, the WidgetA can be inside layout of another widget, or be by itself.

ThThoma

I know this is an old post, but I can't seem to find a solution.

To recap, I have the same problem:
A floating widget (Qt::Tool | Qt::FramelessWindowHint ) that tracks another widget, let's call it the placeholder.

So the placeholder is inside a layout and as such has a parent. I want the floating widget to follow the rect of the placeholder.

The setup (what I know/assume) :

the floating widget has a valid pointer to the placeholder and can do anything to it.
the placeholder has a parent. So it does not receive any move events.
ideally, the solution can be achieved from within the floating/placeholder classes.

My thoughts so far:

The floating widget has a timer and periodically changes itself to follow the placeholder. -> This does not seem like a great idea, if the timer is too fast, we are wasting resources and if the timer is too slow, the user might move the window containing the placeholder, and the delay will be noticeable.
The floating widget installs an event filter, not to catch any QEvent::Move, but to catch QEvent::WindowActivate that all the child widgets receive after a move is complete (please correct me if this is not the case). There will be a delay, yes, until the user completes the window movement but for now acceptable (cheaper than timer). -> Problem? What if the placeholder is placed inside a widget that is scrollable (QScrollArea::setWidget())? It won't receive QEvent::WindowActivate, but the placeholder parent widget (the widget inside the QScrollArea) will actually move! And this leads me to:
The floating widget installs an event filter to the whole parent hierarchy, to catch the actual QEvent::Move . Starting from the placeholder and going up on parentWidget() until we find nullptr we install an eventFilter listening on QEvent::Move and probably to QEvent::ParentChange to fix the event filtering in case some dynamic reparenting happens. How bad of a solution is this?

I'd love your feedback on this.

kshegunov

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

The floating widget has a timer and periodically changes itself to follow the placeholder. -> This does not seem like a great idea, if the timer is too fast, we are wasting resources and if the timer is too slow, the user might move the window containing the placeholder, and the delay will be noticeable.

Agreed. This seems like an ugly clutch.

The floating widget installs an event filter, not to catch any QEvent::Move, but to catch QEvent::WindowActivate that all the child widgets receive after a move is complete (please correct me if this is not the case). There will be a delay, yes, until the user completes the window movement but for now acceptable (cheaper than timer). -> Problem? What if the placeholder is placed inside a widget that is scrollable (QScrollArea::setWidget())? It won't receive QEvent::WindowActivate, but the placeholder parent widget (the widget inside the QScrollArea) will actually move! And this leads me to:

Eh, I'm not sure you're guaranteed to get that event, it may be platform specific.

The floating widget installs an event filter to the whole parent hierarchy, to catch the actual QEvent::Move . Starting from the placeholder and going up on parentWidget() until we find nullptr we install an eventFilter listening on QEvent::Move and probably to QEvent::ParentChange to fix the event filtering in case some dynamic reparenting happens. How bad of a solution is this?

Almost what I get off the top of my head. You can still keep the pointer to the placeholder, but on "attachment" you traverse the object hierarchy up until you get a widget that has the Qt::Window flag set (i.e. it's a top-level window). Then you install the event filter on that widget. Bear in mind that if the placeholder changes ancestry, you may need to respond to the appropriate event and remove the event filter from the old object, and install it to the new top-level window.