parent() not returning the "parent" QWidget given to constructor, why?

DasCapschen

I have a problem, the parent() function does not return the same object that I passed into the constructor. Thus, when I ((MainWindow*)parent())->function(); I get a segfault... not nice...

so I checked why this happens with a bunch of qDebug()s... this is what I got...

MainWindow Contructor, this                      == 0x7ffc53ce97f0
FileList Constructor, parent()                   == 0x7ffc53ce97f0
FileList Function, parent()                      == 0x557b8c8c9170
parent()->parent()->parent()->parent()->parent() == 0x7ffc53ce97f0

so... where do 4 parent objects come from, that I never created? And it seems they only spawn into existance AFTER my constructor ran... so it's not like it's the superclass constructor that causes this...

I mean I guess I could just save the parent I give to the constructor as a member variable (or just call parent() five times...), but doesn't that kind of defeat the purpose of parent()?

I'd like to know, WHY does this happen? And what can I do about it?

raven-worx

@DasCapschen
this depends on your code.
If you call QMainWindow::setCentralWidget() for example your widget is reparented. No matter what parent you passed at construction time

VRonin

@DasCapschen said in parent() not returning the "parent" QWidget given to constructor, why?:

WHY does this happen?

Layouts and container widgets re-parent anything that is passed to them.

And what can I do about it?

Good OOP design works as a 1 way tree, the parent knows about the child but the child assumes and knows nothing about the parent so ((MainWindow*)parent())->function(); is very bad design. the child should emit a signal and the parent should connect to that signal to run the function() slot

mrjj

Hi
As the others says, this should be done via signal and slots for a much better design.

However, the cast is also suboptimal and dangerous. ( as your segfault tells you :)
This will not crash if parent is not what you think.

MainWindow* mywin = qobject_cast<MainWindow* > ( parent() ) ;
if (mywin) mywin->function();