Drag&drop in other window

SGaist

Hi and welcome to devnet,

Which version of Qt are you using ?
On which OS ?
Can you provide a complete minimal compilable example that shows that behaviour ?

mrjj

Hi
Is that this example?
https://doc.qt.io/qt-5/qtwidgets-draganddrop-puzzle-example.html

I tried to make puzzleWidget fullscreen but it still worked.
alt text

magicDM

I think, that problem connected with widget attributes:
Widget

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>

class Widget : public QWidget
{
	Q_OBJECT
public:
	explicit Widget(QWidget *parent = nullptr);

	void turnOnFullscreen();

	void dragEnterEvent(QDragEnterEvent *event) override;
	void dropEvent(QDropEvent *event) override;

signals:

};

#endif // WIDGET_H

// ==========================================================
#include "widget.h"

#include <QApplication>
#include <QWindow>
#include <QDragEnterEvent>
#include <QDropEvent>
#include <QDebug>

Widget::Widget(QWidget *parent) : QWidget(parent)
{
	setAcceptDrops(true);
	setAttribute(Qt::WA_NativeWindow); // comment it, to fix problem
	setAttribute(Qt::WA_AcceptTouchEvents);
	setAutoFillBackground(false);
	setUpdatesEnabled(true);
	setFocusPolicy(Qt::StrongFocus);
	setMouseTracking(true);
	setTabletTracking(true);

	setMinimumSize(600, 600);
	setMaximumSize(600, 600);
}

void Widget::turnOnFullscreen()
{
	if (!windowState().testFlag(Qt::WindowFullScreen))
	{
		if (auto parent = parentWidget())
		{
			setWindowIcon(parent->windowIcon());
		}
		setParent(nullptr);

		const auto& screens = QApplication::screens();
		const int screenNumber = 0;
		if (screenNumber >= 0 && screenNumber < screens.size())
		{
			show();
			windowHandle()->setScreen(screens[screenNumber]);
		}

		showFullScreen();
		activateWindow();
		raise();
		setFocus();
	}
}

void Widget::dragEnterEvent(QDragEnterEvent *event)
{
	event->accept();
}

void Widget::dropEvent(QDropEvent *event)
{
	qInfo() << "Drop";
	event->accept();
}

MainWindow:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

class MainWindow : public QMainWindow
{
	Q_OBJECT

public:
	MainWindow(QWidget *parent = nullptr);
	~MainWindow();
};
#endif // MAINWINDOW_H

// ======================================
#include "mainwindow.h"
#include "widget.h"

#include <QCheckBox>
#include <QVBoxLayout>
#include <QFrame>

MainWindow::MainWindow(QWidget *parent)
	: QMainWindow(parent)
{
	QFrame *frame = new QFrame;
	QVBoxLayout* layout = new QVBoxLayout(frame);
	Widget* widget = new Widget();
	widget->setStyleSheet("background-color:white;");

	QCheckBox* checkBox = new QCheckBox("fullscreen");

	connect(checkBox, &QCheckBox::stateChanged, [=](int state){
		if(state == Qt::Checked)
		{
			if(widget)
			{
				widget->turnOnFullscreen();
			}
		}
		else
		{
			// ...
		}
	});


	layout->addWidget(widget);
	layout->addWidget(checkBox);

	setCentralWidget(frame);
}

MainWindow::~MainWindow()
{
}

#include "mainwindow.h"

#include <QApplication>

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
	MainWindow w;
	w.show();
	return a.exec();
}

If comment line: setAttribute(Qt::WA_NativeWindow); that drag&drop correct work for other window, but documentation nothing say about it, i think it's bug. OS: windows, QT 15.14.2 MSVC 2017 x64

mrjj

Hi
I tried
puzzleWidget->setAttribute(Qt::WA_NativeWindow);
but it still worked.
This is Qt 5.14.2, window 10. vs2017

magicDM

@mrjj Are you using this code to turn on fullscreen?

void PuzzleWidget::turnOnFullscreen()
{
	if (!windowState().testFlag(Qt::WindowFullScreen))
	{
		if (auto parent = parentWidget())
		{
			setWindowIcon(parent->windowIcon());
		}
		setParent(nullptr);

		const auto& screens = QApplication::screens();
		const int screenNumber = 0;
		if (screenNumber >= 0 && screenNumber < screens.size())
		{
			show();
			windowHandle()->setScreen(screens[screenNumber]);
		}

		showFullScreen();
		activateWindow();
		raise();
		setFocus();
	}
}

Now, i checked, that in my PC incorrect behavior is continues. You can run code (it's full), that i mentioned below

mrjj

@magicDM
Well i just did

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    setupMenus();
    setupWidgets();
    setSizePolicy(QSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed));
    setWindowTitle(tr("Puzzle"));

    puzzleWidget->setParent(nullptr);
    puzzleWidget->show();    
    puzzleWidget->showFullScreen();
    puzzleWidget->activateWindow();
    puzzleWidget->raise();
    puzzleWidget->setFocus();
    puzzleWidget->setAttribute(Qt::WA_NativeWindow);

}

So it seems the same except the monitor handling but i only have one monitor so seems pretty much the same.

mrjj

@mrjj
Ok tried yours turnOnFullscreen()
just for kick and still working.

I go fullscreen from start. Do you start up in normal mode and then swap ?

magicDM

@mrjj Yes, now i'm comment windowHandle()->setScreen(screens[screenNumber]); and drag and drop fine work, may be something wrong with it. I go in normal mode, and then via checkbox change state to fullscreen mode

mrjj

@magicDM
Hi
If i wait and use the menu to call turnOnFullscreen then it stops working and shows
the red not accepted on whole form.

magicDM

@mrjj This code should simulate problem:

#include <QApplication>
#include <QMainWindow>
#include <QWidget>
#include <QTextEdit>
#include <QHBoxLayout>
#include <QCheckBox>
#include <QDebug>

class Widget : public QTextEdit
{
public:
	Widget(QWidget* parent = nullptr) : QTextEdit(parent) {
		setAcceptDrops(true);
		setAttribute(Qt::WA_NativeWindow);
		setAttribute(Qt::WA_AcceptTouchEvents);
		setAutoFillBackground(false);
		setUpdatesEnabled(true);
		setFocusPolicy(Qt::StrongFocus);
		setMouseTracking(true);
		setTabletTracking(true);
	}
	void turnOnFullscreen()
	{
		if (!windowState().testFlag(Qt::WindowFullScreen))
		{
			setParent(nullptr);
			show();
			showFullScreen();
			activateWindow();
			raise();
			setFocus();
		}
	}
};

class MMainWindow : public QMainWindow
{
public:
	MMainWindow(QWidget* parent = nullptr) : QMainWindow(parent)
	{
		QHBoxLayout* layout = new QHBoxLayout(this);
		Widget* textEdit = new Widget(this);
		QCheckBox* checkBox = new QCheckBox("Fullscreen mode", this);
		QTextEdit* dragText = new QTextEdit("Text for drag and drop", this);
		dragText->setReadOnly(true);

		connect(checkBox, &QCheckBox::stateChanged, [=](int state){
			if(state == Qt::Checked)
			{
				textEdit->turnOnFullscreen();
			}
		});

		layout->addWidget(textEdit);
		layout->addWidget(dragText);
		layout->addWidget(checkBox);

		QWidget* window = new QWidget(this);
		window->setLayout(layout);
		setCentralWidget(window);
	}
};

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
	MMainWindow w;
	w.show();
	return a.exec();
}

magicDM

A bug reported: https://bugreports.qt.io/browse/QTBUG-85775