Qt GUI design programmatically - qt

Question

I'm try to create a GUI application.
The main window, a QMainWindow, contains 9 labels with fixed size and also the size of the main window.
I tried to make it programmatically without Qt GUI Designer. The project is built without error but I cannot see any label nor layout shown on the main window. it's just blank.
Here is my source code:
WCwindow::WCwindow()
{
// initialize widgets with text
CAM111 = new QLabel("CAM 01");
CAM121 = new QLabel("CAM 02");
CAM131 = new QLabel("CAM 03");
CAM211 = new QLabel("CAM 04");
CAM221 = new QLabel("CAM 05");
CAM231 = new QLabel("CAM 06");
CAM311 = new QLabel("CAM 07");
CAM321 = new QLabel("CAM 08");
CAM331 = new QLabel("CAM 09");
CAM111->setFixedSize(wcW,wcH);
CAM121->setFixedSize(wcW,wcH);
CAM131->setFixedSize(wcW,wcH);
CAM211->setFixedSize(wcW,wcH);
CAM221->setFixedSize(wcW,wcH);
CAM231->setFixedSize(wcW,wcH);
CAM311->setFixedSize(wcW,wcH);
CAM321->setFixedSize(wcW,wcH);
CAM331->setFixedSize(wcW,wcH);
QGridLayout *layout = new QGridLayout;
layout->addWidget(CAM111,0,0);
layout->addWidget(CAM121,0,1);
layout->addWidget(CAM131,0,2);
layout->addWidget(CAM211,1,0);
layout->addWidget(CAM221,1,1);
layout->addWidget(CAM231,1,2);
layout->addWidget(CAM311,2,0);
layout->addWidget(CAM321,2,1);
layout->addWidget(CAM331,2,2);
setLayout(layout);
setWindowTitle("Camera Window");
setFixedSize(1000, 800);
}
of course, the class is initialized and evoked in main.cpp:
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
WCwindow *WCwin = new WCwindow;
WCwin->show();
return app.exec();
}
what kind of bug am I having??

Answer 1

The code below works fine. The problem was in the code you weren't showing. When you use a QMainWindow, as you've eventually admitted to doing, you need to set its centralWidget with a new widget that you construct.
// main.cpp
#include <QVector>
#include <QMainWindow>
#include <QLabel>
#include <QGridLayout>
#include <QApplication>
class WCwindow : public QMainWindow
{
public:
WCwindow();
private:
QVector<QLabel*> cams;
QLabel* cam(int r, int c) const {
return cams[r*3 + c];
}
};
WCwindow::WCwindow()
{
QGridLayout *layout = new QGridLayout;
for (int i = 1; i < 10; ++ i) {
QLabel * const label = new QLabel(QString("CAM %1").arg(i, 2, 10, QLatin1Char('0')));
label->setFixedSize(200, 50);
layout->addWidget(label, (i-1) / 3, (i-1) % 3);
cams << label;
}
QWidget * central = new QWidget();
setCentralWidget(central);
centralWidget()->setLayout(layout);
setWindowTitle("Camera Window");
setFixedSize(1000, 800);
}
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
WCwindow win;
win.show();
return app.exec();
}

Answer 2

Is WCwindow a subclass of QMainWindow? In that case i would advise to remove the layout from your window in the GUI editor by clicking the "break layout" button in the top bar, then use the following:
//setup all your labels and layout ...
//creating a QWidget, and setting the WCwindow as parent
QWidget * widget = new QWidget(this);
//set the gridlayout for the widget
widget->setLayout(layout);
//setting the WCwindow's central widget
setCentralWidget(widget);