I have now created an independent example: (Sorry it does not use an .ui file)

main.cpp
Qt Code: 
  1. #include <qt/qapplication.h>
  2. #include "MainWindow.h"
  3.  
  4. int main(int argc, char** argv)
  5. {
  6. 	QApplication app( argc, argv );
  7. 	MainWindow mainWindow;	
  8. 	mainWindow.show();
  9. 	return app.exec();
  10. }
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MainWindow.h
Qt Code: 
  1. #ifndef MAINWINDOW_H_
  2. #define MAINWINDOW_H_
  3.  
  4. #include <QtGui/QApplication>
  5. #include <QtGui/QGridLayout>
  6. #include <QtGui/QMainWindow>
  7. #include <QtGui/QTextEdit>
  8. #include <QtGui/QWidget>
  9.  
  10. class MainWindow : public QMainWindow
  11. {
  12. 	Q_OBJECT
  13. public:
  14.     QWidget *m_centralwidget;
  15.     QWidget *gridLayout;
  16.     QGridLayout *gridLayout1;
  17.     QTextEdit *textEdit;
  18.  
  19.     void setupUi(QMainWindow *MainWindow)
  20.     {
  21. 		MainWindow->resize(500, 500);
  22. 		m_centralwidget = new QWidget(MainWindow);
  23.  
  24. 		QSizePolicy sizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
  25. 		sizePolicy.setHorizontalStretch(0);
  26. 		sizePolicy.setVerticalStretch(0);
  27. 		m_centralwidget->setSizePolicy(sizePolicy);
  28.  
  29. 		gridLayout = new QWidget(m_centralwidget);
  30. 		gridLayout->setGeometry(QRect(50, 50, 300, 200));
  31. 		gridLayout->setSizePolicy(sizePolicy);
  32.  
  33. 		textEdit = new QTextEdit(gridLayout);
  34.  
  35. 		gridLayout1 = new QGridLayout(gridLayout);
  36. 		gridLayout1->setContentsMargins(0, 0, 0, 0);
  37. 		gridLayout1->addWidget(textEdit, 0, 0, 1, 1);
  38.  
  39. 		MainWindow->setCentralWidget(m_centralwidget);
  40.  
  41. 		QMetaObject::connectSlotsByName(MainWindow);
  42.     } // setupUi
  43.  
  44. public:
  45. 	MainWindow(QWidget* parent = 0, Qt::WFlags flags = 0);
  46.  
  47. 	virtual ~MainWindow(){};
  48. 	//void resizeEvent(QResizeEvent * /* event */);
  49.  
  50. };
  51. #endif
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MainWindow.cpp
Qt Code: 
  1. #include "MainWindow.h"
  2. //
  3. MainWindow::MainWindow(QWidget* parent /*= 0*/, Qt::WFlags flags /*= 0*/) : QMainWindow(parent, flags)
  4. {
  5. 	setupUi(this);
  6. }
  7.  
  8. //void MainWindow::resizeEvent(QResizeEvent * /* event */)
  9. //{
  10. //	gridLayout->setGeometry(QRect(0, 0, this->width(), this->height()));
  11. //}
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In this example nothing is resized if I resize the dialog.

Matthias