get the last QWidget actived

bozo6919

I found this signal : QApplication::focusChanged(QWidget *old, QWidget *new)
And it's work for what I want to do.
But, this function sends me the most little child of all my widgets. So I have implemented this function :

template <class T>T findParent(QObject *child)
{
	T r = 0;

	if (!child)
		return nullptr;
	QObject *parent = child->parent();
	
	while (parent) {
		r = dynamic_cast<T> (parent);
		if (r)
			return r;
		parent = parent->parent();
	}
	return r;
}

And it's working with "findParent<LayoutPanelTabber *>(new);"
Thanks

mrjj

@bozo6919
Hi
Should dynamic_cast not be qobject_cast ?

bozo6919

@mrjj
Hi yes but I have some problems with qobject_cast :
"Error C2338 qobject_cast requires the type to have a Q_OBJECT macro"
But in my class, I have the macro :

class ProjectManager : public QObject
{
	Q_OBJECT

public:
	// Some function...
	template <class T>
	T findParent(QObject *child)
	{
		T r = nullptr;

		if (!child)
			return nullptr;
		QObject *parent = child->parent();

		while (parent) {
			r = qobject_cast<T>(parent);
			if (r)
				return r;
			parent = parent->parent();
		}
		return r;
	}
};

JonB

@bozo6919
I don't know what the answer is and I don't do C++, but

r = qobject_cast<T>(parent);
"Error C2338 qobject_cast requires the type to have a Q_OBJECT macro"

This will be complaining about the Q_OBJECT on parent or on type T (not sure which, perhaps the latter) not on your class, won't it?

mrjj

@bozo6919
Hi
Ah maybe it don't like templates as T don't exist yet.
So if static check, there is no way for it to know if contains Q_OBJECT
or not.

JonB

@mrjj said in get the last QWidget actived:

Ah maybe it don't like templates as T don't exist yet.

That's what I was wondering/suspecting....

bozo6919

Yes, it's what I was suspecting too, but in my class, if I call qobject_cast with T = ContentPanelEditor *, who is contained in the same project and have the macro Q_OBJECT, I have the same error...

Edit:
No, I misread. ^^' after the qobject_cast on my ContentPanelEditor, I have another cast for a class in another project. So he doesn't know about this class.
This other class is contained in a dll. There is a way to apply qobject_cast on it?

SGaist

Hi,

Can you give more details about that chain of casts ?

bozo6919

Hi,

My program has two projects :

one is a DLL.
the other an EXE.
In my EXE, I have to apply a qobject_cast on a class who is contained in my DLL.
But if I put in this class (in the DLL) the macro Q_OBJECT, my IDE (visual studio 2017) cannot compile the project with an error of linking.

SGaist

Is your .dll project also managed with Qt ?

bozo6919

Yes, theses projects was made with Qt

SGaist

Then there should be no problem with qobject_cast.

bozo6919

Yes, but I have problems, and I don't know yet how to resolve them

SGaist

What exact problems ?

bozo6919

Hi, sorry for my late

This problem for example :

#pragma once

#include <QtCore/qobject.h>

class __declspec(dllexport) LayoutManager : public QObject
{
	Q_OBJECT

public:
	template <class T>T findParent(QObject *child)
	{
		T r = nullptr;

		if (!child)
			return nullptr;
		QObject *parent = child->parent();

		while (parent) {
			r = qobject_cast<T>(parent);
			if (r)
				return r;
			parent = parent->parent();
		}
		return r;
	}
};

And I have this error message :
Error : C2338 : qobject_cast requires the type to have a Q_OBJECT macro

But the macro is here. So instead of qobject_cast, I have to use dynamic_cast

SGaist

What type are you looking for ?

bozo6919

This is a type who doesn't exist in this project. I use this function in another project

SGaist

And is that type a QObject based class with Q_OBJECT in it's declaration ?

@bozo6919 said in get the last QWidget actived:

class __declspec(dllexport) LayoutManager : public QObject

On a side note, Qt provides macros to properly handle the export/import stuff. See here.