Layout Problem

[Seema Rao]

Hi all I have problem in adding QLabel to the layout of the widget. It never appears on the widget, here is the code I have written. I have derived a class from QMainWindow and here is the code,

MainWindow::MainWindow()
{

first= new QWidget;
second= new QWidget;
third= new QWidget;

middleWindow();

QHBoxLayout *mainLayout= new QHBoxLayout;
mainLayout->addWidget(first);
mainLayout->addWidget(second);
mainLayout->addWidget(third);
.
.
.
}

void MainWindow::middleWindow()
{
imageLabel=new QLabel;

imageLabel->setBackgroundRole(QPalette::Base);
imageLabel->setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
imageLabel->setScaledContents(true);

// Load the Centre image

QImage image("images/middle.bmp");
imageLabel->setPixmap(QPixmap::fromImage(image));
QVBoxLayout *d= new QVBoxLayout;
d->addWidget(imageLabel);
second->setLayout(d);

}

I dont know why label doesnt appear on the second widget. Have I missed anything, in the Layout code?

Thanks in advance,
Seema Rao

[Sarma]

hi seema,
That was quite well. But u have not mentioned the parents for these labels. Try this code:

MainWindow::MainWindow()
{
 
first= new QWidget(this);
second= new QWidget(this);
third= new QWidget(this);
 
middleWindow();
 
QHBoxLayout *mainLayout= new QHBoxLayout(this);
mainLayout->addWidget(first);
mainLayout->addWidget(second);
mainLayout->addWidget(third);
.
.
.
}
 
void MainWindow::middleWindow()
{
imageLabel=new QLabel(this);
 
imageLabel->setBackgroundRole(QPalette::Base);
imageLabel->setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
imageLabel->setScaledContents(true);
 
// Load the Centre image
 
QImage image("images/middle.bmp");
imageLabel->setPixmap(QPixmap::fromImage(image));
QVBoxLayout *d= new QVBoxLayout(this);
d->addWidget(imageLabel);
second->setLayout(d);
}

MainWindow::MainWindow()
{

first= new QWidget(this);
second= new QWidget(this);
third= new QWidget(this);

middleWindow();

QHBoxLayout *mainLayout= new QHBoxLayout(this);
mainLayout->addWidget(first);
mainLayout->addWidget(second);
mainLayout->addWidget(third);
.
.
.
}

void MainWindow::middleWindow()
{
imageLabel=new QLabel(this);

imageLabel->setBackgroundRole(QPalette::Base);
imageLabel->setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
imageLabel->setScaledContents(true);

// Load the Centre image

QImage image("images/middle.bmp");
imageLabel->setPixmap(QPixmap::fromImage(image));
QVBoxLayout *d= new QVBoxLayout(this);
d->addWidget(imageLabel);
second->setLayout(d);
}

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Please let me know what happenned.

Regards,
sarma.

[SkripT]

You could try calling to show for the label, too

[Seema Rao]

Event though I specify the parent as you had said it doesnt work. I have simplified the program and here is the whole code,

//mainwindow.h
#include <QMainWindow>
class QWidget;
class QLabel;

class MainWindow : public QMainWindow
{
Q_OBJECT

public:
MainWindow();

private:
QWidget *first;
QWidget *second;
QWidget *third;
QLabel *imageLabel;
void middleWindow();
};


//mainwindow.cpp
#include <QtGui>
#include "mainwindow.h"

MainWindow::MainWindow()
{

first= new QWidget(this);
second= new QWidget(this);
third= new QWidget(this);

middleWindow();

QHBoxLayout *mainLayout= new QHBoxLayout;
mainLayout->addWidget(first);
mainLayout->addWidget(second);
mainLayout->addWidget(third);

}

void MainWindow::middleWindow()
{

imageLabel=new QLabel("HILABEL");

QVBoxLayout *d= new QVBoxLayout(second);
d->addWidget(imageLabel);
second->setLayout(d);
imageLabel->show();

}

//main.cpp
#include <QApplication>
#include "mainwindow.h"

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

I dont know why, may be I have to subclass the second widget and in the constructor of that class I have to add the layout that binds the QLabel

[jpn]

- Call base class constructor in MainWindow ctor
- Where do you apply that mainLayout? Create a "central" widget, set mainLayout as it's layout, and set the "central" widget as mainwindow's central widget.

MainWindow::MainWindow() : QMainWindow()
{
	...
 
	QHBoxLayout* mainLayout = new QHBoxLayout;
	mainLayout->addWidget(first);
	mainLayout->addWidget(second);
	mainLayout->addWidget(third);
 
	QWidget* central = new QWidget;
	central->setLayout(mainLayout);
	setCentralWidget(central);
}

MainWindow::MainWindow() : QMainWindow()
{
	...

	QHBoxLayout* mainLayout = new QHBoxLayout;
	mainLayout->addWidget(first);
	mainLayout->addWidget(second);
	mainLayout->addWidget(third);

	QWidget* central = new QWidget;
	central->setLayout(mainLayout);
	setCentralWidget(central);
}

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