Why does QT DLL process calls this class from .exe process give an access violation?

mirro

the following link Error screenshot
link Error screenshot

//dll code

#include <QtWidgets/QWidget>
#include "qtdll_global.h"

class QTDLL_EXPORT widgetdll : public QWidget
{
	Q_OBJECT

public:
	widgetdll(QWidget *parent = 0,HWND hwnd = 0);
	~widgetdll();
};
#include "widgetdll.h"
#include <QWindow>
#include <QMessageBox>
widgetdll::widgetdll(QWidget *parent,HWND hwnd)
	: QWidget(parent)
{
        setFixedSize(600, 400);
	//
	QWindow *container = QWindow::fromWinId((WId)hwnd);

	container->show();
}

widgetdll::~widgetdll()
{

}

.exe code

#include <QtWidgets/QMainWindow>
#include "ui_callDll.h"

class callDll : public QMainWindow
{
	Q_OBJECT

public:
	callDll(QWidget *parent = 0);
	~callDll();

private:
	Ui::callDllClass ui;
};

#include "callDll.h"
#include "widgetdll.h"
#include <QtWidgets/QLayout>
#include <QWindow>
#include <QPushButton>
callDll::callDll(QWidget *parent)
	: QMainWindow(parent)
{
	ui.setupUi(this);
	QWidget  *pUserWidget = new QWidget;
	pUserWidget->setObjectName(QString::fromUtf8("Sub Window"));
	pUserWidget->setFixedSize(600, 400);
	pUserWidget->setWindowTitle("Sub Window");

	WId hwndParentWidget = pUserWidget->effectiveWinId();
	widgetdll * p = new widgetdll(0,(HWND)hwndParentWidget);
	p->show();

	setWindowTitle("Parent Window");
	setObjectName("Parent Window");
}

callDll::~callDll()
{

}

mrjj

Hi
If you do
QWindow *container = QWindow::fromWinId((WId)hwnd);
if ( container )
container->show();

does it still crash ?

mirro

@mrjj

Cannot the following code be used in another process?

QWindow *container = QWindow::fromWinId((WId)hwnd);

mrjj

@mirro said in Why does QT DLL process calls this class from .exe process give an access violation?:

fromWinId

Docs sounds like it can.
https://doc.qt.io/qt-5/qwindow.html#fromWinId

so if you check for NULL you no longer crash ?

mirro

@mrjj

If the null pointer is checked, the program does not crash.

Can't the following code be used in another process?

QWindow *container = QWindow::fromWinId((WId)hwnd);

Bonnie

@mirro
Have you checked that if hwnd / hwndParentWidget is a valid value?

mirro

@Bonnie How to convert Hwnd to Wid?

Bonnie

@mirro
I don't mean that.
I've tested your code with

    QWidget  *pUserWidget = new QWidget;
    pUserWidget->setObjectName(QString::fromUtf8("Sub Window"));
    pUserWidget->setFixedSize(600, 400);
    pUserWidget->setWindowTitle("Sub Window");

    WId hwndParentWidget = pUserWidget->effectiveWinId();
    qDebug() << hwndParentWidget;

And the value of hwndParentWidget is 0.
So I ask you if you've checked that.
If the hwnd is 0, then it is reasonable that the result of QWindow::fromWinId is nullptr.

mirro

@Bonnie
thank you.
is (HWND)hwndParentWidget null value?
How to convert WId to HWND?

callDll::callDll(QWidget *parent)
	: QMainWindow(parent)
{
	ui.setupUi(this);
	//
	QWidget  *pUserWidget = new QWidget;
	pUserWidget->setObjectName(QString::fromUtf8("another progress widget"));
	pUserWidget->setFixedSize(600, 400);
	pUserWidget->setWindowTitle("another progress widget");
	WId hwndParentWidget = pUserWidget->effectiveWinId();
	widgetdll * p = new widgetdll(0,(HWND)hwndParentWidget);
	p->show();
}

widgetdll::widgetdll(QWidget *parent,HWND hwnd)
	: QWidget(parent)
{
	//
	QWindow *container = QWindow::fromWinId((WId)hwnd);
	if (container)
		container->show();
}

Bonnie

@mirro
Your conversion has no problem.
But I think you should use winId() instead of effectiveWinId()