Question

Here is a pruned version of a problem I have using QT/linux. The program runs, but the size of the displayed widget is wrong (the contents, frame + labels, does not fit).

I understood that the size of a windows should be computed fron its contents (children). Why is that not happening properly here?

So the first question is, of course why this is happening.

The real program actually updates the contents of the widget at run-time. I have tried to simulate that behavior by the insertion of the main_window->show() (commented //SHOW1). If this first show() call is made, then the second show() does not show the new contents the widget. I have tried with update without success…

 #include <QApplication>
 #include <QtCore>
 #include <QMainWindow>
 #include <QTabWidget>
 #include <QWidget>
 #include <QGroupBox>
 #include <QVBoxLayout>
 #include <QLabel>

 #include <stdlib.h>


 int main(int argc, char *argv[])
 {
     QApplication app(argc, argv);
     QMainWindow* main_window = new(QMainWindow);
    main_window->setObjectName("main_window");
    main_window->resize(800, 600);
    main_window->setWindowTitle("Hello");

    QTabWidget* node_tab_widget = new QTabWidget(main_window);
 //    node_tab_widget->setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
 //    node_tab_widget->setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
    node_tab_widget->setObjectName(QString::fromUtf8("tab_widget"));
    node_tab_widget->resize(500, 400);

     QWidget* w= new QWidget(node_tab_widget);
     node_tab_widget->addTab(w, "TAB");

     //main_window->show();  //SHOW1
     QGroupBox* group_widget = new QGroupBox("GROUPNAME", w);
     QVBoxLayout*  group_layout = new QVBoxLayout;
     group_widget->setLayout(group_layout);
     group_layout->addWidget((QLabel*)new QLabel(">>>>>>>>>>>>>>>>>>>>>>>>>here1"));
     group_layout->addWidget((QLabel*)new QLabel("here2"));
 //     group_widget->setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);


     main_window->update();
     main_window->show();
     return app.exec();
 }

Answer 1

I don’t really understand what is the result you expect, can be something like what you get from this code:

#include <QApplication>
#include <QtCore>
#include <QMainWindow>
#include <QTabWidget>
#include <QWidget>
#include <QGroupBox>
#include <QVBoxLayout>
#include <QLabel>
#include <stdlib.h>

int main(int argc, char *argv[]) {

 QApplication app(argc, argv);
 QMainWindow* main_window = new(QMainWindow);
 main_window->setObjectName("main_window");
 main_window->resize(800, 600);
 main_window->setWindowTitle("Hello");

 QTabWidget* node_tab_widget = new QTabWidget();
 node_tab_widget->setObjectName(QString::fromUtf8("tab_widget"));
 node_tab_widget->resize(500, 400);

 QWidget* w= new QWidget();
 node_tab_widget->addTab(w, "TAB");

 QGroupBox* group_widget = new QGroupBox("GROUPNAME", w);
 QVBoxLayout*  group_layout = new QVBoxLayout;
 group_widget->setLayout(group_layout);
 group_layout->addWidget((QLabel*)new QLabel(">>>>>>>>>>>>>>>>>>>>>>>>>here1"));
 group_layout->addWidget((QLabel*)new QLabel("here2"));

 QVBoxLayout*  gl = new QVBoxLayout;
 gl->addWidget(group_widget);

 main_window->setCentralWidget(node_tab_widget);
 main_window->show();
 return app.exec();
}

which add the QTabWidget node_tab_widget as central widget, with a tab TAB.

The tab contain the QGroupBox GROUPNAME with the two labels (vertical aligned)