Change background color of a custom widget

[rubikon]

Hello.

Creating a QWidget and change its background colour works fine. But if I try the same with a custom widget which inherits for QWidget it won't work.

This is an minamal example which shows this behaviour:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QMainWindow>
 
namespace Ui {
class MainWindow;
}
 
class MyWidget : public QWidget
{
	Q_OBJECT
 
	public:
		explicit MyWidget(QWidget *parent = 0);
};
 
class MainWindow : public QMainWindow
{
	Q_OBJECT
 
	public:
		explicit MainWindow(QWidget *parent = 0);
		~MainWindow();
 
	private slots:
		void on_pushButton_clicked();
 
	private:
		Ui::MainWindow *ui;
		QWidget *m_pMyWidget;
};
 
#endif // MAINWINDOW_H

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MyWidget : public QWidget
{
	Q_OBJECT

	public:
		explicit MyWidget(QWidget *parent = 0);
};

class MainWindow : public QMainWindow
{
	Q_OBJECT
	
	public:
		explicit MainWindow(QWidget *parent = 0);
		~MainWindow();

	private slots:
		void on_pushButton_clicked();

	private:
		Ui::MainWindow *ui;
		QWidget *m_pMyWidget;
};

#endif // MAINWINDOW_H

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#include "mainwindow.h"
#include "ui_mainwindow.h"
 
MyWidget::MyWidget(QWidget *parent) :
	QWidget(parent)
{
 
}
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
	ui->setupUi(this);
}
 
MainWindow::~MainWindow()
{
	delete ui;
}
 
void MainWindow::on_pushButton_clicked()
{
	//m_pMyWidget = new QWidget(this);		// <= Works !!!
	m_pMyWidget = new MyWidget(this);		// <= Does not work !!!
	m_pMyWidget->setGeometry(0,0,300,100);
	m_pMyWidget->setStyleSheet("background-color:black;");
	m_pMyWidget->show();
}

#include "mainwindow.h"
#include "ui_mainwindow.h"

MyWidget::MyWidget(QWidget *parent) :
	QWidget(parent)
{

}

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
	ui->setupUi(this);
}

MainWindow::~MainWindow()
{
	delete ui;
}

void MainWindow::on_pushButton_clicked()
{
	//m_pMyWidget = new QWidget(this);		// <= Works !!!
	m_pMyWidget = new MyWidget(this);		// <= Does not work !!!
	m_pMyWidget->setGeometry(0,0,300,100);
	m_pMyWidget->setStyleSheet("background-color:black;");
	m_pMyWidget->show();
}

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What am I doing wrong?

[high_flyer]

show your MyWidget implementation.

[rubikon]

It's already in my first post: second Qt Code Line 4 to Line 8.

[high_flyer]

works perfectly for me...
Try a clean and rebuild.

[rubikon]

I've tried clean and rebuild. But it is still not working. I've tried Qt 4.8.1 (with MinGW and MSVC2008) and Qt 4.7.4 (with MinGW 4.4 and MSVC2008) all four in QtCreator 2.4.0

[high_flyer]

Did you post your real code?
Post your poroject here in a zip and I will try it.

[rubikon]

Yes this is the real code. I've attached the zip file.

[high_flyer]

Remove the Q_OBJECT macro from your MyWidget subclass - you wont have signals/slots then.
I don't have the time or mental resources to think why this is a problem though - or what you are doing wrong.
Also, you are shadowing your own MainWindow class name with the Ui::MainWindow - give them different names.

[corrected]

[rubikon]

If I remove the Q_OBJECT macro changing the background colour works. But then it seems that I can't define signals:

class MyWidget : public QWidget
{
//Q_OBJECT

public:
explicit MyWidget(QWidget *parent = 0);

signals:
void mySignal();

};

The compiler says:

mainwindow.h:20: Error: Class declarations lacks Q_OBJECT macro.
mingw32-make.exe[1]: *** [release/moc_mainwindow.cpp] Error 1
mingw32-make.exe: *** [release] Error 2

[high_flyer]

sorry, when you use a QWidget direct subclass you need to re implement the paintEvent() as follows:
http://qt-project.org/doc/qt-4.8/sty...qwidget-widget

(I wonder why when Q_OBJECT is omitted from the subclass it does work....? don't see where the connection is at the moment...)

[rubikon]

Edit: This seems to work.

Thank you!