Move a window by clicking an internal widget instead of title bar

Question

In Windows when I create a QMainWindow I can move it around the screen by clicking the title bar and dragging it.

In my application I\'ve hidden the title bar by using <

Answer 1

This is an example on how to implement a fake title bar, that has standard buttons (minimize, maximize, close), and can be dragged to move the whole window (this is based on the approach in @Kevin's answer).

#include 


class FakeTitleBar : public QWidget{
    Q_OBJECT
public:
    explicit FakeTitleBar(QWidget* parent= nullptr):QWidget(parent){
        label.setSizePolicy(QSizePolicy::Expanding,
                            QSizePolicy::Expanding);
        layout.addWidget(&label);
        layout.addWidget(&buttonMinimize);
        layout.addWidget(&buttonMaximize);
        layout.addWidget(&buttonClose);
        //connecting buttons' signals to slots
        connect(&buttonMinimize, &QPushButton::clicked,
                this, &FakeTitleBar::MinimizeWindow);
        connect(&buttonMaximize, &QPushButton::clicked,
                this, &FakeTitleBar::MaximizeWindow);
        connect(&buttonClose, &QPushButton::clicked,
                this, &FakeTitleBar::CloseWindow);
        //setting vertical fixed size policy
        //so that the title bar does not take up any additional space
        setSizePolicy(QSizePolicy::Preferred, QSizePolicy::Fixed);
        //a bit of styling
        setStyleSheet("QPushButton {margin:0px; padding:5px;}"
                      "QWidget {background-color:blue; color:white;}");
    }

public slots:
    //slots for corresponding buttons
    void MinimizeWindow(){
        window()->showMinimized();
    }
    void MaximizeWindow(){
        if(!window()->isMaximized())
            window()->showMaximized();
        else
            window()->showNormal();
    }
    void CloseWindow(){
        window()->close();
    }

protected:
    void mousePressEvent(QMouseEvent* event){
        //save the press position (this is relative to the current widget)
        pressPos= event->pos();
        isMoving= true;
    }
    void mouseMoveEvent(QMouseEvent* event){
        //isMoving flag makes sure that the drag and drop event originated
        //from within the titlebar, because otherwise the window shouldn't be moved
        if(isMoving){
            //calculate difference between the press position and the new Mouse position
            //(this is relative to the current widget)
            QPoint diff= event->pos() - pressPos;
            //move the window by diff
            window()->move(window()->pos()+diff);
        }
    }
    void mouseReleaseEvent(QMouseEvent* /*event*/){
        //drag and drop operation end
        isMoving= false;
    }
    //double-clicking on the title bar should maximize the window
    void mouseDoubleClickEvent(QMouseEvent* /*event*/){
        MaximizeWindow();
    }
    //in order for the style sheet to apply on this custom widget
    //see https://doc.qt.io/qt-5/stylesheet-reference.html#qwidget-widget
    void paintEvent(QPaintEvent *)
    {
        QStyleOption opt;
        opt.init(this);
        QPainter p(this);
        style()->drawPrimitive(QStyle::PE_Widget, &opt, &p, this);
    }

private:
    QHBoxLayout layout{this};
    QLabel label{"Fake Title Bar"};
    QPushButton buttonMinimize{"-"};
    QPushButton buttonMaximize{"M"};
    QPushButton buttonClose{"X"};
    QPoint pressPos;
    bool isMoving{false};
};

//sample usage

class Widget : public QWidget{
public:
    explicit Widget(QWidget* parent= nullptr):QWidget(parent){
        setWindowFlags(Qt::CustomizeWindowHint);
        layout.addWidget(&titleBar);
        layout.addWidget(&label);
        layout.setContentsMargins(0, 0, 0, 0);
        label.setAlignment(Qt::AlignCenter);
        //default size for the window
        resize(320,240);
    }
    ~Widget(){}

private:
    QVBoxLayout layout{this};
    FakeTitleBar titleBar;
    QLabel label{"this is a sample window"};
};

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

    Widget w;
    w.show();

    return app.exec();
}

#include "main.moc"