QMainWindow Class

The QMainWindow class provides a main application window. More...

Header: #include <QMainWindow>
qmake: QT += widgets
Inherits: QWidget

Public Types

enum DockOption { AnimatedDocks, AllowNestedDocks, AllowTabbedDocks, ForceTabbedDocks, VerticalTabs, GroupedDragging }
flags DockOptions


Public Functions

QMainWindow(QWidget *parent = nullptr, Qt::WindowFlags flags = Qt::WindowFlags())
virtual ~QMainWindow()
void addDockWidget(Qt::DockWidgetArea area, QDockWidget *dockwidget)
void addDockWidget(Qt::DockWidgetArea area, QDockWidget *dockwidget, Qt::Orientation orientation)
void addToolBar(Qt::ToolBarArea area, QToolBar *toolbar)
void addToolBar(QToolBar *toolbar)
QToolBar *addToolBar(const QString &title)
void addToolBarBreak(Qt::ToolBarArea area = Qt::TopToolBarArea)
QWidget *centralWidget() const
Qt::DockWidgetArea corner(Qt::Corner corner) const
virtual QMenu *createPopupMenu()
QMainWindow::DockOptions dockOptions() const
Qt::DockWidgetArea dockWidgetArea(QDockWidget *dockwidget) const
bool documentMode() const
QSize iconSize() const
void insertToolBar(QToolBar *before, QToolBar *toolbar)
void insertToolBarBreak(QToolBar *before)
bool isAnimated() const
bool isDockNestingEnabled() const
QMenuBar *menuBar() const
QWidget *menuWidget() const
void removeDockWidget(QDockWidget *dockwidget)
void removeToolBar(QToolBar *toolbar)
void removeToolBarBreak(QToolBar *before)
void resizeDocks(const QList<QDockWidget *> &docks, const QList<int> &sizes, Qt::Orientation orientation)
bool restoreDockWidget(QDockWidget *dockwidget)
bool restoreState(const QByteArray &state, int version = 0)
QByteArray saveState(int version = 0) const
void setCentralWidget(QWidget *widget)
void setCorner(Qt::Corner corner, Qt::DockWidgetArea area)
void setDockOptions(QMainWindow::DockOptions options)
void setDocumentMode(bool enabled)
void setIconSize(const QSize &iconSize)
void setMenuBar(QMenuBar *menuBar)
void setMenuWidget(QWidget *menuBar)
void setStatusBar(QStatusBar *statusbar)
void setTabPosition(Qt::DockWidgetAreas areas, QTabWidget::TabPosition tabPosition)
void setTabShape(QTabWidget::TabShape tabShape)
void setToolButtonStyle(Qt::ToolButtonStyle toolButtonStyle)
void splitDockWidget(QDockWidget *first, QDockWidget *second, Qt::Orientation orientation)
QStatusBar *statusBar() const
QTabWidget::TabPosition tabPosition(Qt::DockWidgetArea area) const
QTabWidget::TabShape tabShape() const
QList<QDockWidget *> tabifiedDockWidgets(QDockWidget *dockwidget) const
void tabifyDockWidget(QDockWidget *first, QDockWidget *second)
QWidget *takeCentralWidget()
Qt::ToolBarArea toolBarArea(QToolBar *toolbar) const
bool toolBarBreak(QToolBar *toolbar) const
Qt::ToolButtonStyle toolButtonStyle() const
bool unifiedTitleAndToolBarOnMac() const

Public Slots

void setAnimated(bool enabled)
void setDockNestingEnabled(bool enabled)
void setUnifiedTitleAndToolBarOnMac(bool set)


void iconSizeChanged(const QSize &iconSize)
void tabifiedDockWidgetActivated(QDockWidget *dockWidget)
void toolButtonStyleChanged(Qt::ToolButtonStyle toolButtonStyle)

Reimplemented Protected Functions

virtual void contextMenuEvent(QContextMenuEvent *event) override
virtual bool event(QEvent *event) override

Detailed Description

Qt Main Window Framework

A main window provides a framework for building an application's user interface. Qt has QMainWindow and its related classes for main window management. QMainWindow has its own layout to which you can add QToolBars, QDockWidgets, a QMenuBar, and a QStatusBar. The layout has a center area that can be occupied by any kind of widget. You can see an image of the layout below.

Note: Creating a main window without a central widget is not supported. You must have a central widget even if it is just a placeholder.

Creating Main Window Components

A central widget will typically be a standard Qt widget such as a QTextEdit or a QGraphicsView. Custom widgets can also be used for advanced applications. You set the central widget with setCentralWidget().

Main windows have either a single (SDI) or multiple (MDI) document interface. You create MDI applications in Qt by using a QMdiArea as the central widget.

We will now examine each of the other widgets that can be added to a main window. We give examples on how to create and add them.

Creating Menus

Qt implements menus in QMenu and QMainWindow keeps them in a QMenuBar. QActions are added to the menus, which display them as menu items.

You can add new menus to the main window's menu bar by calling menuBar(), which returns the QMenuBar for the window, and then add a menu with QMenuBar::addMenu().

QMainWindow comes with a default menu bar, but you can also set one yourself with setMenuBar(). If you wish to implement a custom menu bar (i.e., not use the QMenuBar widget), you can set it with setMenuWidget().

An example of how to create menus follows:

    void MainWindow::createMenus()
        fileMenu = menuBar()->addMenu(tr("&File"));

The createPopupMenu() function creates popup menus when the main window receives context menu events. The default implementation generates a menu with the checkable actions from the dock widgets and toolbars. You can reimplement createPopupMenu() for a custom menu.

Creating Toolbars

Toolbars are implemented in the QToolBar class. You add a toolbar to a main window with addToolBar().

You control the initial position of toolbars by assigning them to a specific Qt::ToolBarArea. You can split an area by inserting a toolbar break - think of this as a line break in text editing - with addToolBarBreak() or insertToolBarBreak(). You can also restrict placement by the user with QToolBar::setAllowedAreas() and QToolBar::setMovable().

The size of toolbar icons can be retrieved with iconSize(). The sizes are platform dependent; you can set a fixed size with setIconSize(). You can alter the appearance of all tool buttons in the toolbars with setToolButtonStyle().

An example of toolbar creation follows:

    void MainWindow::createToolBars()
        fileToolBar = addToolBar(tr("File"));

Creating Dock Widgets

Dock widgets are implemented in the QDockWidget class. A dock widget is a window that can be docked into the main window. You add dock widgets to a main window with addDockWidget().

There are four dock widget areas as given by the Qt::DockWidgetArea enum: left, right, top, and bottom. You can specify which dock widget area that should occupy the corners where the areas overlap with setCorner(). By default each area can only contain one row (vertical or horizontal) of dock widgets, but if you enable nesting with setDockNestingEnabled(), dock widgets can be added in either direction.

Two dock widgets may also be stacked on top of each other. A QTabBar is then used to select which of the widgets should be displayed.

We give an example of how to create and add dock widgets to a main window:

    QDockWidget *dockWidget = new QDockWidget(tr("Dock Widget"), this);
    dockWidget->setAllowedAreas(Qt::LeftDockWidgetArea |
    addDockWidget(Qt::LeftDockWidgetArea, dockWidget);

The Status Bar

You can set a status bar with setStatusBar(), but one is created the first time statusBar() (which returns the main window's status bar) is called. See QStatusBar for information on how to use it.

Storing State

QMainWindow can store the state of its layout with saveState(); it can later be retrieved with restoreState(). It is the position and size (relative to the size of the main window) of the toolbars and dock widgets that are stored.

See also QMenuBar, QToolBar, QStatusBar, QDockWidget, Application Example, Dock Widgets Example, MDI Example, SDI Example, and Menus Example.

Member Type Documentation

enum QMainWindow::DockOption
flags QMainWindow::DockOptions

This enum contains flags that specify the docking behavior of QMainWindow.

QMainWindow::AnimatedDocks0x01Identical to the animated property.
QMainWindow::AllowNestedDocks0x02Identical to the dockNestingEnabled property.
QMainWindow::AllowTabbedDocks0x04The user can drop one dock widget "on top" of another. The two widgets are stacked and a tab bar appears for selecting which one is visible.
QMainWindow::ForceTabbedDocks0x08Each dock area contains a single stack of tabbed dock widgets. In other words, dock widgets cannot be placed next to each other in a dock area. If this option is set, AllowNestedDocks has no effect.
QMainWindow::VerticalTabs0x10The two vertical dock areas on the sides of the main window show their tabs vertically. If this option is not set, all dock areas show their tabs at the bottom. Implies AllowTabbedDocks. See also setTabPosition().
QMainWindow::GroupedDragging0x20When dragging the titlebar of a dock, all the tabs that are tabbed with it are going to be dragged. Implies AllowTabbedDocks. Does not work well if some QDockWidgets have restrictions in which area they are allowed. (This enum value was added in Qt 5.6.)

These options only control how dock widgets may be dropped in a QMainWindow. They do not re-arrange the dock widgets to conform with the specified options. For this reason they should be set before any dock widgets are added to the main window. Exceptions to this are the AnimatedDocks and VerticalTabs options, which may be set at any time.

This enum was introduced or modified in Qt 4.3.

The DockOptions type is a typedef for QFlags<DockOption>. It stores an OR combination of DockOption values.

Property Documentation

animated : bool

This property holds whether manipulating dock widgets and tool bars is animated

When a dock widget or tool bar is dragged over the main window, the main window adjusts its contents to indicate where the dock widget or tool bar will be docked if it is dropped. Setting this property causes QMainWindow to move its contents in a smooth animation. Clearing this property causes the contents to snap into their new positions.

By default, this property is set. It may be cleared if the main window contains widgets which are slow at resizing or repainting themselves.

Setting this property is identical to setting the AnimatedDocks option using setDockOptions().

This property was introduced in Qt 4.2.

Access functions:

bool isAnimated() const
void setAnimated(bool enabled)

dockNestingEnabled : bool

This property holds whether docks can be nested

If this property is false, dock areas can only contain a single row (horizontal or vertical) of dock widgets. If this property is true, the area occupied by a dock widget can be split in either direction to contain more dock widgets.

Dock nesting is only necessary in applications that contain a lot of dock widgets. It gives the user greater freedom in organizing their main window. However, dock nesting leads to more complex (and less intuitive) behavior when a dock widget is dragged over the main window, since there are more ways in which a dropped dock widget may be placed in the dock area.

Setting this property is identical to setting the AllowNestedDocks option using setDockOptions().

This property was introduced in Qt 4.2.

Access functions:

bool isDockNestingEnabled() const
void setDockNestingEnabled(bool enabled)

dockOptions : DockOptions

This property holds the docking behavior of QMainWindow

The default value is AnimatedDocks | AllowTabbedDocks.

This property was introduced in Qt 4.3.

Access functions:

QMainWindow::DockOptions dockOptions() const
void setDockOptions(QMainWindow::DockOptions options)

documentMode : bool

This property holds whether the tab bar for tabbed dockwidgets is set to document mode.

The default is false.

This property was introduced in Qt 4.5.

Access functions:

bool documentMode() const
void setDocumentMode(bool enabled)

See also QTabBar::documentMode.

iconSize : QSize

size of toolbar icons in this mainwindow.

The default is the default tool bar icon size of the GUI style. Note that the icons used must be at least of this size as the icons are only scaled down.

Access functions:

QSize iconSize() const
void setIconSize(const QSize &iconSize)

tabShape : QTabWidget::TabShape

This property holds the tab shape used for tabbed dock widgets.

The default is QTabWidget::Rounded.

This property was introduced in Qt 4.5.

Access functions:

QTabWidget::TabShape tabShape() const
void setTabShape(QTabWidget::TabShape tabShape)

See also setTabPosition().

toolButtonStyle : Qt::ToolButtonStyle

style of toolbar buttons in this mainwindow.

To have the style of toolbuttons follow the system settings, set this property to Qt::ToolButtonFollowStyle. On Unix, the user settings from the desktop environment will be used. On other platforms, Qt::ToolButtonFollowStyle means icon only.

The default is Qt::ToolButtonIconOnly.

Access functions:

Qt::ToolButtonStyle toolButtonStyle() const
void setToolButtonStyle(Qt::ToolButtonStyle toolButtonStyle)

unifiedTitleAndToolBarOnMac : bool

This property holds whether the window uses the unified title and toolbar look on macOS

Note that the Qt 5 implementation has several limitations compared to Qt 4:

  • Use in windows with OpenGL content is not supported. This includes QGLWidget and QOpenGLWidget.
  • Using dockable or movable toolbars may result in painting errors and is not recommended

This property was introduced in Qt 5.2.

Access functions:

bool unifiedTitleAndToolBarOnMac() const
void setUnifiedTitleAndToolBarOnMac(bool set)

Member Function Documentation

QMainWindow::QMainWindow(QWidget *parent = nullptr, Qt::WindowFlags flags = Qt::WindowFlags())

Constructs a QMainWindow with the given parent and the specified widget flags.

QMainWindow sets the Qt::Window flag itself, and will hence always be created as a top-level widget.

[signal] void QMainWindow::iconSizeChanged(const QSize &iconSize)

This signal is emitted when the size of the icons used in the window is changed. The new icon size is passed in iconSize.

You can connect this signal to other components to help maintain a consistent appearance for your application.

See also setIconSize().

[signal] void QMainWindow::tabifiedDockWidgetActivated(QDockWidget *dockWidget)

This signal is emitted when the tabified dock widget is activated by selecting the tab. The activated dock widget is passed in dockWidget.

This function was introduced in Qt 5.8.

See also tabifyDockWidget() and tabifiedDockWidgets().

[signal] void QMainWindow::toolButtonStyleChanged(Qt::ToolButtonStyle toolButtonStyle)

This signal is emitted when the style used for tool buttons in the window is changed. The new style is passed in toolButtonStyle.

You can connect this signal to other components to help maintain a consistent appearance for your application.

See also setToolButtonStyle().

[virtual] QMainWindow::~QMainWindow()

Destroys the main window.

void QMainWindow::addDockWidget(Qt::DockWidgetArea area, QDockWidget *dockwidget)

Adds the given dockwidget to the specified area.

void QMainWindow::addDockWidget(Qt::DockWidgetArea area, QDockWidget *dockwidget, Qt::Orientation orientation)

Adds dockwidget into the given area in the direction specified by the orientation.

void QMainWindow::addToolBar(Qt::ToolBarArea area, QToolBar *toolbar)

Adds the toolbar into the specified area in this main window. The toolbar is placed at the end of the current tool bar block (i.e. line). If the main window already manages toolbar then it will only move the toolbar to area.

See also insertToolBar(), addToolBarBreak(), and insertToolBarBreak().

void QMainWindow::addToolBar(QToolBar *toolbar)

This is an overloaded function.

Equivalent of calling addToolBar(Qt::TopToolBarArea, toolbar)

QToolBar *QMainWindow::addToolBar(const QString &title)

This is an overloaded function.

Creates a QToolBar object, setting its window title to title, and inserts it into the top toolbar area.

See also setWindowTitle().

void QMainWindow::addToolBarBreak(Qt::ToolBarArea area = Qt::TopToolBarArea)

Adds a toolbar break to the given area after all the other objects that are present.

QWidget *QMainWindow::centralWidget() const

Returns the central widget for the main window. This function returns zero if the central widget has not been set.

See also setCentralWidget().

[override virtual protected] void QMainWindow::contextMenuEvent(QContextMenuEvent *event)

Reimplements: QWidget::contextMenuEvent(QContextMenuEvent *event).

Qt::DockWidgetArea QMainWindow::corner(Qt::Corner corner) const

Returns the dock widget area that occupies the specified corner.

See also setCorner().

[virtual] QMenu *QMainWindow::createPopupMenu()

Returns a popup menu containing checkable entries for the toolbars and dock widgets present in the main window. If there are no toolbars and dock widgets present, this function returns nullptr.

By default, this function is called by the main window when the user activates a context menu, typically by right-clicking on a toolbar or a dock widget.

If you want to create a custom popup menu, reimplement this function and return a newly-created popup menu. Ownership of the popup menu is transferred to the caller.

See also addDockWidget(), addToolBar(), and menuBar().

Qt::DockWidgetArea QMainWindow::dockWidgetArea(QDockWidget *dockwidget) const

Returns the Qt::DockWidgetArea for dockwidget. If dockwidget has not been added to the main window, this function returns Qt::NoDockWidgetArea.

See also addDockWidget(), splitDockWidget(), and Qt::DockWidgetArea.

[override virtual protected] bool QMainWindow::event(QEvent *event)

Reimplements: QWidget::event(QEvent *event).

void QMainWindow::insertToolBar(QToolBar *before, QToolBar *toolbar)

Inserts the toolbar into the area occupied by the before toolbar so that it appears before it. For example, in normal left-to-right layout operation, this means that toolbar will appear to the left of the toolbar specified by before in a horizontal toolbar area.

See also insertToolBarBreak(), addToolBar(), and addToolBarBreak().

void QMainWindow::insertToolBarBreak(QToolBar *before)

Inserts a toolbar break before the toolbar specified by before.

Returns the menu bar for the main window. This function creates and returns an empty menu bar if the menu bar does not exist.

If you want all windows in a Mac application to share one menu bar, don't use this function to create it, because the menu bar created here will have this QMainWindow as its parent. Instead, you must create a menu bar that does not have a parent, which you can then share among all the Mac windows. Create a parent-less menu bar this way:

QMenuBar *menuBar = new QMenuBar(nullptr);

See also setMenuBar().

Returns the menu bar for the main window. This function returns null if a menu bar hasn't been constructed yet.

This function was introduced in Qt 4.2.

See also setMenuWidget().

void QMainWindow::removeDockWidget(QDockWidget *dockwidget)

Removes the dockwidget from the main window layout and hides it. Note that the dockwidget is not deleted.

void QMainWindow::removeToolBar(QToolBar *toolbar)

Removes the toolbar from the main window layout and hides it. Note that the toolbar is not deleted.

void QMainWindow::removeToolBarBreak(QToolBar *before)

Removes a toolbar break previously inserted before the toolbar specified by before.

void QMainWindow::resizeDocks(const QList<QDockWidget *> &docks, const QList<int> &sizes, Qt::Orientation orientation)

Resizes the dock widgets in the list docks to the corresponding size in pixels from the list sizes. If orientation is Qt::Horizontal, adjusts the width, otherwise adjusts the height of the dock widgets. The sizes will be adjusted such that the maximum and the minimum sizes are respected and the QMainWindow itself will not be resized. Any additional/missing space is distributed amongst the widgets according to the relative weight of the sizes.


    resizeDocks({blueWidget, yellowWidget}, {20 , 40}, Qt::Horizontal);

If the blue and the yellow widget are nested on the same level they will be resized such that the yellowWidget is twice as big as the blueWidget

If some widgets are grouped in tabs, only one widget per group should be specified. Widgets not in the list might be changed to respect the constraints.

This function was introduced in Qt 5.6.

bool QMainWindow::restoreDockWidget(QDockWidget *dockwidget)

Restores the state of dockwidget if it is created after the call to restoreState(). Returns true if the state was restored; otherwise returns false.

See also restoreState() and saveState().

bool QMainWindow::restoreState(const QByteArray &state, int version = 0)

Restores the state of this mainwindow's toolbars and dockwidgets. Also restores the corner settings too. The version number is compared with that stored in state. If they do not match, the mainwindow's state is left unchanged, and this function returns false; otherwise, the state is restored, and this function returns true.

To restore geometry saved using QSettings, you can use code like this:

void MainWindow::readSettings()
    QSettings settings("MyCompany", "MyApp");

See also saveState(), QWidget::saveGeometry(), QWidget::restoreGeometry(), and restoreDockWidget().

QByteArray QMainWindow::saveState(int version = 0) const

Saves the current state of this mainwindow's toolbars and dockwidgets. This includes the corner settings which can be set with setCorner(). The version number is stored as part of the data.

The objectName property is used to identify each QToolBar and QDockWidget. You should make sure that this property is unique for each QToolBar and QDockWidget you add to the QMainWindow

To restore the saved state, pass the return value and version number to restoreState().

To save the geometry when the window closes, you can implement a close event like this:

void MyMainWindow::closeEvent(QCloseEvent *event)
    QSettings settings("MyCompany", "MyApp");
    settings.setValue("geometry", saveGeometry());
    settings.setValue("windowState", saveState());

See also restoreState(), QWidget::saveGeometry(), and QWidget::restoreGeometry().

void QMainWindow::setCentralWidget(QWidget *widget)

Sets the given widget to be the main window's central widget.

Note: QMainWindow takes ownership of the widget pointer and deletes it at the appropriate time.

See also centralWidget().

void QMainWindow::setCorner(Qt::Corner corner, Qt::DockWidgetArea area)

Sets the given dock widget area to occupy the specified corner.

See also corner().

void QMainWindow::setMenuBar(QMenuBar *menuBar)

Sets the menu bar for the main window to menuBar.

Note: QMainWindow takes ownership of the menuBar pointer and deletes it at the appropriate time.

See also menuBar().

void QMainWindow::setMenuWidget(QWidget *menuBar)

Sets the menu bar for the main window to menuBar.

QMainWindow takes ownership of the menuBar pointer and deletes it at the appropriate time.

This function was introduced in Qt 4.2.

See also menuWidget().

void QMainWindow::setStatusBar(QStatusBar *statusbar)

Sets the status bar for the main window to statusbar.

Setting the status bar to nullptr will remove it from the main window. Note that QMainWindow takes ownership of the statusbar pointer and deletes it at the appropriate time.

See also statusBar().

void QMainWindow::setTabPosition(Qt::DockWidgetAreas areas, QTabWidget::TabPosition tabPosition)

Sets the tab position for the given dock widget areas to the specified tabPosition. By default, all dock areas show their tabs at the bottom.

Note: The VerticalTabs dock option overrides the tab positions set by this method.

This function was introduced in Qt 4.5.

See also tabPosition() and setTabShape().

void QMainWindow::splitDockWidget(QDockWidget *first, QDockWidget *second, Qt::Orientation orientation)

Splits the space covered by the first dock widget into two parts, moves the first dock widget into the first part, and moves the second dock widget into the second part.

The orientation specifies how the space is divided: A Qt::Horizontal split places the second dock widget to the right of the first; a Qt::Vertical split places the second dock widget below the first.

Note: if first is currently in a tabbed docked area, second will be added as a new tab, not as a neighbor of first. This is because a single tab can contain only one dock widget.

Note: The Qt::LayoutDirection influences the order of the dock widgets in the two parts of the divided area. When right-to-left layout direction is enabled, the placing of the dock widgets will be reversed.

See also tabifyDockWidget(), addDockWidget(), and removeDockWidget().

QStatusBar *QMainWindow::statusBar() const

Returns the status bar for the main window. This function creates and returns an empty status bar if the status bar does not exist.

See also setStatusBar().

QTabWidget::TabPosition QMainWindow::tabPosition(Qt::DockWidgetArea area) const

Returns the tab position for area.

Note: The VerticalTabs dock option overrides the tab positions returned by this function.

This function was introduced in Qt 4.5.

See also setTabPosition() and tabShape().

QList<QDockWidget *> QMainWindow::tabifiedDockWidgets(QDockWidget *dockwidget) const

Returns the dock widgets that are tabified together with dockwidget.

This function was introduced in Qt 4.5.

See also tabifyDockWidget().

void QMainWindow::tabifyDockWidget(QDockWidget *first, QDockWidget *second)

Moves second dock widget on top of first dock widget, creating a tabbed docked area in the main window.

See also tabifiedDockWidgets().

QWidget *QMainWindow::takeCentralWidget()

Removes the central widget from this main window.

The ownership of the removed widget is passed to the caller.

This function was introduced in Qt 5.2.

Qt::ToolBarArea QMainWindow::toolBarArea(QToolBar *toolbar) const

Returns the Qt::ToolBarArea for toolbar. If toolbar has not been added to the main window, this function returns Qt::NoToolBarArea.

See also addToolBar(), addToolBarBreak(), and Qt::ToolBarArea.

bool QMainWindow::toolBarBreak(QToolBar *toolbar) const

Returns whether there is a toolbar break before the toolbar.

See also addToolBarBreak() and insertToolBarBreak().

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