How can I add items to a layout in Qt?

Question

I am developing an application in Qt 4.8.4, in which I do the following:

I subclass QGridLayout as follows:

class Viewer : public QGridLayout
{
    Q_OBJECT
    ...................
private:
    // Objects
    /// Maximize button object
    ViewerGeneric* viewerGeneric;

    /// Maximize button object
    QPushButton* btnMaximize;

    /// Close button object
    QPushButton* btnClose;

    /// Connect button object
    QPushButton* btnConnect;

    /// Central viewer layout object
    QGridLayout* viewer;

    /// Indicates the row position in the main grid
    unsigned int row;

    /// Indicates the column position in the main grid
    unsigned int col;
};

Then in the constructor I do something like this:

// Create the objects
btnMaximize = new QPushButton("max");
btnClose = new QPushButton("close");
btnConnect = new QPushButton("connect");

// Add the horizontal toolbar
QHBoxLayout* toolbar = new QHBoxLayout();
toolbar->setSizeConstraint(QLayout::SetMinimumSize);
toolbar->addItem(new QSpacerItem(0, 0, 
                     QSizePolicy::Expanding, QSizePolicy::Minimum));
toolbar->addWidget(btnMaximize);
toolbar->addWidget(btnClose);

// Add the 'Connect' button
viewer = new QGridLayout();
viewer->addWidget(btnConnect);

// Add the widgets
this->addItem(toolbar, 0, 0);
this->addItem(viewer, 0, 0, 2);

But, in the end, when I show the Viewer class in my main window the window is completely blank! Hope anybody can help me. Thank you.

Cheers,

Answer 1

If parent widget is already visible, you need to call show() method of the later added widgets to make them visible.

Answer 2

Finally I have found the solution:

For adding layouts into layouts, use addLayout() function instead of addItem(). I do not really know which is the difference but it works.

Thanks for your comments!