QApplication 类

QApplication 类管理 GUI 应用程序的控制流和主要设置。 更多...

Header: #include <QApplication>
CMake: find_package(Qt6 COMPONENTS Widgets REQUIRED)
target_link_libraries(mytarget PRIVATE Qt6::Widgets)
qmake: QT += widgets
继承: QGuiApplication



QApplication (int & argc , char ** argv )
virtual ~QApplication ()
QString styleSheet () const


virtual bool notify (QObject * receiver , QEvent * e ) override


void aboutQt ()
bool autoSipEnabled () const
void closeAllWindows ()
void setAutoSipEnabled (const bool enabled )
void setStyleSheet (const QString & sheet )


void focusChanged (QWidget * old , QWidget * now )


QWidget * activeModalWidget ()
QWidget * activePopupWidget ()
QWidget * activeWindow ()
void alert (QWidget * widget , int msec = 0)
QWidgetList allWidgets ()
void beep ()
int cursorFlashTime ()
int doubleClickInterval ()
int exec ()
QWidget * focusWidget ()
QFont font ()
QFont font (const QWidget * widget )
QFont font (const char * className )
bool isEffectEnabled (Qt::UIEffect effect )
int keyboardInputInterval ()
Qt::NavigationMode navigationMode ()
QPalette palette (const QWidget * widget )
QPalette palette (const char * className )
void setActiveWindow (QWidget * active )
void setCursorFlashTime (int)
void setDoubleClickInterval (int)
void setEffectEnabled (Qt::UIEffect effect , bool enable = true)
void setFont (const QFont & font , const char * className = nullptr)
void setKeyboardInputInterval (int)
void setNavigationMode (Qt::NavigationMode mode )
void setPalette (const QPalette & palette , const char * className = nullptr)
void setStartDragDistance (int l )
void setStartDragTime (int ms )
void setStyle (QStyle * style )
QStyle * setStyle (const QString & style )
void setWheelScrollLines (int)
int startDragDistance ()
int startDragTime ()
QStyle * style ()
QWidget * topLevelAt (const QPoint & point )
QWidget * topLevelAt (int x , int y )
QWidgetList topLevelWidgets ()
int wheelScrollLines ()
QWidget * widgetAt (const QPoint & point )
QWidget * widgetAt (int x , int y )


virtual bool event (QEvent * e ) override


QApplication 专攻 QGuiApplication with some functionality needed for QWidget -based applications. It handles widget specific initialization, finalization.

For any GUI application using Qt, there is precisely one QApplication object, no matter whether the application has 0, 1, 2 or more windows at any given time. For non- QWidget based Qt applications, use QGuiApplication instead, as it does not depend on the QtWidgets 库。

Some GUI applications provide a special batch mode ie. provide command line arguments for executing tasks without manual intervention. In such non-GUI mode, it is often sufficient to instantiate a plain QCoreApplication to avoid unnecessarily initializing resources needed for a graphical user interface. The following example shows how to dynamically create an appropriate type of application instance:

QCoreApplication* createApplication(int &argc, char *argv[])
    for (int i = 1; i < argc; ++i) {
        if (!qstrcmp(argv[i], "-no-gui"))
            return new QCoreApplication(argc, argv);
    return new QApplication(argc, argv);
int main(int argc, char* argv[])
    QScopedPointer<QCoreApplication> app(createApplication(argc, argv));
    if (qobject_cast<QApplication *>( {
       // start GUI version...
    } else {
       // start non-GUI version...
    return app->exec();

The QApplication object is accessible through the instance () function that returns a pointer equivalent to the global qApp 指针。

QApplication 的主要职责领域:

  • It initializes the application with the user's desktop settings such as palette (), font () 和 doubleClickInterval (). It keeps track of these properties in case the user changes the desktop globally, for example through some kind of control panel.
  • It performs event handling, meaning that it receives events from the underlying window system and dispatches them to the relevant widgets. By using sendEvent () 和 postEvent () you can send your own events to widgets.
  • It parses common command line arguments and sets its internal state accordingly. See the constructor documentation below for more details.
  • It defines the application's look and feel, which is encapsulated in a QStyle object. This can be changed at runtime with setStyle ().
  • It provides localization of strings that are visible to the user via translate ().
  • It provides some magical objects like the clipboard ().
  • 它知道有关应用程序的窗口。可以询问在某个位置是哪个 Widget 使用 widgetAt (),获取列表为 topLevelWidgets () 和 closeAllWindows (),等。
  • It manages the application's mouse cursor handling, see setOverrideCursor ()

Since the QApplication object does so much initialization, it must be created before any other objects related to the user interface are created. QApplication also deals with common command line arguments. Hence, it is usually a good idea to create it before any interpretation or modification of argv is done in the application itself.

另请参阅 QCoreApplication , QAbstractEventDispatcher , QEventLoop ,和 QSettings .


autoSipEnabled : bool

toggles automatic SIP (software input panel) visibility

把此特性设为 true to automatically display the SIP when entering widgets that accept keyboard input. This property only affects widgets with the WA_InputMethodEnabled attribute set, and is typically used to launch a virtual keyboard on devices which have very few or no keys.

The property only has an effect on platforms that use software input panels.

The default is platform dependent.


bool autoSipEnabled () const
void setAutoSipEnabled (const bool enabled )

cursorFlashTime : int

This property holds the text cursor's flash (blink) time in milliseconds

The flash time is the time required to display, invert and restore the caret display. Usually the text cursor is displayed for half the cursor flash time, then hidden for the same amount of time, but this may vary.

The default value on X11 is 1000 milliseconds. On Windows, the Control Panel value is used and setting this property sets the cursor flash time for all applications.

We recommend that widgets do not cache this value as it may change at any time if the user changes the global desktop settings.

注意: This property may hold a negative value, for instance if cursor blinking is disabled.


int cursorFlashTime ()
void setCursorFlashTime (int)

doubleClickInterval : int

This property holds the time limit in milliseconds that distinguishes a double click from two consecutive mouse clicks

在 X11 默认值为 400 毫秒。在Windows 和 Mac OS 使用操作系统的值。


int doubleClickInterval ()
void setDoubleClickInterval (int)

keyboardInputInterval : int

此特性以毫秒为单位保持 (区分键按下和两次连续键按下的) 时间限制

在 X11 默认值为 400 毫秒。在Windows 和 Mac OS 使用操作系统的值。


int keyboardInputInterval ()
void setKeyboardInputInterval (int)

startDragDistance : int

This property holds the minimum distance required for a drag and drop operation to start.

If you support drag and drop in your application, and want to start a drag and drop operation after the user has moved the cursor a certain distance with a button held down, you should use this property's value as the minimum distance required.

For example, if the mouse position of the click is stored in startPos and the current position (e.g. in the mouse move event) is currentPos , you can find out if a drag should be started with code like this:

if ((startPos - currentPos).manhattanLength() >=

Qt 使用此值在内部,如在 QFileDialog .

The default value (if the platform doesn't provide a different default) is 10 pixels.


int startDragDistance ()
void setStartDragDistance (int l )

另请参阅 startDragTime (), QPoint::manhattanLength (),和 拖放 .

startDragTime : int

This property holds the time in milliseconds that a mouse button must be held down before a drag and drop operation will begin

If you support drag and drop in your application, and want to start a drag and drop operation after the user has held down a mouse button for a certain amount of time, you should use this property's value as the delay.

Qt also uses this delay internally, e.g. in QTextEdit and QLineEdit , for starting a drag.

默认值为 500 毫秒。


int startDragTime ()
void setStartDragTime (int ms )

另请参阅 startDragDistance () 和 拖放 .

styleSheet : QString

This property holds the application style sheet

By default, this property returns an empty string unless the user specifies the -stylesheet option on the command line when running the application.


QString styleSheet () const
void setStyleSheet (const QString & sheet )

另请参阅 QWidget::setStyle () 和 Qt 样式表 .

wheelScrollLines : int

This property holds the number of lines to scroll a widget, when the mouse wheel is rotated.

If the value exceeds the widget's number of visible lines, the widget should interpret the scroll operation as a single page up or page down . If the widget is an item view class , then the result of scrolling one line depends on the setting of the widget's scroll mode . Scroll one line can mean scroll one item or scroll one pixel .

By default, this property has a value of 3.


int wheelScrollLines ()
void setWheelScrollLines (int)

另请参阅 QStyleHints::wheelScrollLines ().


QApplication:: QApplication ( int & argc , char ** argv )

Initializes the window system and constructs an application object with argc command line arguments in argv .

警告: The data referred to by argc and argv must stay valid for the entire lifetime of the QApplication object. In addition, argc must be greater than zero and argv must contain at least one valid character string.

全局 qApp pointer refers to this application object. Only one application object should be created.

This application object must be constructed before any paint devices (including widgets, pixmaps, bitmaps etc.).

注意: argc and argv might be changed as Qt removes command line arguments that it recognizes.

All Qt programs automatically support the following command line options:

  • -style= style , sets the application GUI style. Possible values depend on your system configuration. If you compiled Qt with additional styles or have additional styles as plugins these will be available to the -style command line option. You can also set the style for all Qt applications by setting the QT_STYLE_OVERRIDE 环境变量。
  • -style style , is the same as listed above.
  • -stylesheet= stylesheet , sets the application styleSheet . The value must be a path to a file that contains the Style Sheet.

    注意: Relative URLs in the Style Sheet file are relative to the Style Sheet file's path.

  • -stylesheet stylesheet , is the same as listed above.
  • -widgetcount, prints debug message at the end about number of widgets left undestroyed and maximum number of widgets existed at the same time
  • -reverse, sets the application's layout direction to Qt::RightToLeft
  • -qmljsdebugger=, activates the QML/JS debugger with a specified port. The value must be of format port:1234[,block], where block is optional and will make the application wait until a debugger connects to it.

另请参阅 QCoreApplication::arguments ().

[static slot] void QApplication:: aboutQt ()

Displays a simple message box about Qt. The message includes the version number of Qt being used by the application.

This is useful for inclusion in the Help menu of an application, as shown in the 菜单 范例。

This function is a convenience slot for QMessageBox::aboutQt ().

[static slot] void QApplication:: closeAllWindows ()


This function is particularly useful for applications with many top-level windows.

The windows are closed in random order, until one window does not accept the close event. The application quits when the last window was successfully closed, unless quitOnLastWindowClosed is set to false. To trigger application termination from e.g. a menu, use QCoreApplication::quit () 而不是此函数。

另请参阅 quitOnLastWindowClosed , lastWindowClosed (), QWidget::close (), QWidget::closeEvent (), lastWindowClosed (), QCoreApplication::quit (), topLevelWidgets (),和 QWidget::isWindow ().

[signal] void QApplication:: focusChanged ( QWidget * old , QWidget * now )

This signal is emitted when the widget that has keyboard focus changed from old to now , i.e., because the user pressed the tab-key, clicked into a widget or changed the active window. Both old and now 可以是 nullptr .

The signal is emitted after both widget have been notified about the change through QFocusEvent .

另请参阅 QWidget::setFocus (), QWidget::clearFocus (),和 Qt::FocusReason .

[virtual] QApplication:: ~QApplication ()

Cleans up any window system resources that were allocated by this application. Sets the global variable qApp to nullptr .

[static] QWidget *QApplication:: activeModalWidget ()

Returns the active modal widget.

A modal widget is a special top-level widget which is a subclass of QDialog that specifies the modal parameter of the constructor as true. A modal widget must be closed before the user can continue with other parts of the program.

Modal widgets are organized in a stack. This function returns the active modal widget at the top of the stack.

另请参阅 activePopupWidget () 和 topLevelWidgets ().

[static] QWidget *QApplication:: activePopupWidget ()

Returns the active popup widget.

A popup widget is a special top-level widget that sets the Qt::WType_Popup widget flag, e.g. the QMenu widget. When the application opens a popup widget, all events are sent to the popup. Normal widgets and modal widgets cannot be accessed before the popup widget is closed.

Only other popup widgets may be opened when a popup widget is shown. The popup widgets are organized in a stack. This function returns the active popup widget at the top of the stack.

另请参阅 activeModalWidget () 和 topLevelWidgets ().

[static] QWidget *QApplication:: activeWindow ()

返回拥有键盘输入聚焦的应用程序顶层窗口,或 nullptr 若应用程序窗口不拥有聚焦。可能存在 activeWindow(),即使没有 focusWidget (),例如:若该窗口的 Widget 不接受键事件。

另请参阅 setActiveWindow (), QWidget::setFocus (), QWidget::hasFocus (),和 focusWidget ().

[static] void QApplication:: alert ( QWidget * widget , int msec = 0)

Causes an alert to be shown for widget if the window is not the active window. The alert is shown for msec miliseconds. If msec is zero (the default), then the alert is shown indefinitely until the window becomes active again.

Currently this function does nothing on Qt for Embedded Linux.

On macOS, this works more at the application level and will cause the application icon to bounce in the dock.

On Windows, this causes the window's taskbar entry to flash for a time. If msec is zero, the flashing will stop and the taskbar entry will turn a different color (currently orange).

On X11, this will cause the window to be marked as "demands attention", the window must not be hidden (i.e. not have hide() called on it, but be visible in some sort of way) in order for this to work.

[static] QWidgetList QApplication:: allWidgets ()

返回应用程序的所有 Widget 的列表。

列表是空的 ( QList::isEmpty ()) 若没有 Widget。

注意: 某些 Widget 可能被隐藏。


void updateAllWidgets()
    const QWidgetList allWidgets = QApplication::allWidgets();
    for (QWidget *widget : allWidgets)

另请参阅 topLevelWidgets () 和 QWidget::isVisible ().

[static] void QApplication:: beep ()

响铃声,使用默认音量和声音。函数 not 可用于 Qt for Embedded Linux。

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

重实现: QGuiApplication::event (QEvent *e).

[static] int QApplication:: exec ()

进入主事件循环并等待,直到 exit () is called, then returns the value that was set to exit () (其为 0 若 exit () 被调用凭借 quit ()).

有必要调用此函数以启动事件处理。主事件循环从窗口系统接收事件,并将其分派给应用程序 Widget。

Generally, no user interaction can take place before calling exec(). As a special case, modal widgets like QMessageBox can be used before calling exec(), because modal widgets call exec() to start a local event loop.

To make your application perform idle processing, i.e., executing a special function whenever there are no pending events, use a QTimer 采用 0 超时。更高级空闲处理方案可以达成使用 processEvents ().

推荐把清理代码连接到 aboutToQuit() 信号,而非将其放入应用程序的 main() function. This is because, on some platforms the QApplication::exec() call may not return. For example, on the Windows platform, when the user logs off, the system terminates the process after Qt closes all top-level windows. Hence, there is no guarantee that the application will have time to exit its event loop and execute code at the end of the main() function, after the QApplication::exec() call.

另请参阅 quitOnLastWindowClosed , QCoreApplication::quit (), QCoreApplication::exit (), QCoreApplication::processEvents (),和 QCoreApplication::exec ().

[static] QWidget *QApplication:: focusWidget ()

返回拥有键盘输入聚焦的应用程序 Widget,或 nullptr 若此应用程序的 Widget 不拥有聚焦。

另请参阅 QWidget::setFocus (), QWidget::hasFocus (), activeWindow (),和 focusChanged ().

[static] QFont QApplication:: font ()


另请参阅 setFont (), fontMetrics (),和 QWidget::font ().

[static] QFont QApplication:: font (const QWidget * widget )


返回默认字体,为 widget 。若未注册默认字体为 widget 类,它返回其最近注册超类的默认字体。

另请参阅 fontMetrics (), setFont (),和 QWidget::setFont ().

[static] QFont QApplication:: font (const char * className )


返回 Widget 字体为给定 className .

另请参阅 setFont () 和 QWidget::font ().

[static] bool QApplication:: isEffectEnabled ( Qt::UIEffect effect )

返回 true if effect 被启用;否则返回 false .

By default, Qt will try to use the desktop settings. To prevent this, call setDesktopSettingsAware(false).

注意: 当低于 16 位颜色深度运行屏幕,禁用所有效果。

另请参阅 setEffectEnabled () 和 Qt::UIEffect .

返回 Qt 使用哪种聚焦导航。

此特征只可用于 Qt for Embedded Linux。

另请参阅 setNavigationMode ().

[override virtual] bool QApplication:: notify ( QObject * receiver , QEvent * e )

重实现: QGuiApplication::notify (QObject *object, QEvent *event).

[static] QPalette QApplication:: palette (const QWidget * widget )

widget is passed, the default palette for the widget's class is returned. This may or may not be the application palette. In most cases there is no special palette for certain types of widgets, but one notable exception is the popup menu under Windows, if the user has defined a special background color for menus in the display settings.

另请参阅 setPalette () 和 QWidget::palette ().

[static] QPalette QApplication:: palette (const char * className )


Returns the palette for widgets of the given className .

另请参阅 setPalette () 和 QWidget::palette ().

[static] void QApplication:: setActiveWindow ( QWidget * active )

Sets the active window to the active widget in response to a system event. The function is called from the platform specific event handlers.

警告: This function does not set the keyboard focus to the active widget. Call QWidget::activateWindow () 代替。

It sets the activeWindow () 和 focusWidget () attributes and sends proper WindowActivate / WindowDeactivate and FocusIn / FocusOut events to all appropriate widgets. The window will then be painted in active state (e.g. cursors in line edits will blink), and it will have tool tips enabled.

另请参阅 activeWindow () 和 QWidget::activateWindow ().

[static] void QApplication:: setEffectEnabled ( Qt::UIEffect effect , bool enable = true)

启用 UI 效果 effect if enable 为 True,否则效果将不会被使用。

注意: 当低于 16 位颜色深度运行屏幕,禁用所有效果。

另请参阅 isEffectEnabled (), Qt::UIEffect ,和 setDesktopSettingsAware ().

[static] void QApplication:: setFont (const QFont & font , const char * className = nullptr)

把默认应用程序字体改为 font 。若 className 有传递,改变仅适用的类继承 className (作为报告通过 QObject::inherits ()).

On application start-up, the default font depends on the window system. It can vary depending on both the window system version and the locale. This function lets you override the default font; but overriding may be a bad idea because, for example, some locales need extra large fonts to support their special characters.

警告: 不要将使用此函数结合 Qt 样式表 . The font of an application can be customized using the "font" style sheet property. To set a bold font for all QPushButtons, set the application styleSheet () as " QPushButton { font: bold }"

另请参阅 font (), fontMetrics (),和 QWidget::setFont ().

[static] void QApplication:: setNavigationMode ( Qt::NavigationMode mode )

将聚焦导航 Qt 应使用的种类设为 mode .

此特征只可用于 Qt for Embedded Linux。

另请参阅 navigationMode ().

[static] void QApplication:: setPalette (const QPalette & palette , const char * className = nullptr)

将应用程序调色板更改为 palette .

className is passed, the change applies only to widgets that inherit className (作为报告通过 QObject::inherits ()). If className is left 0, the change affects all widgets, thus overriding any previously set class specific palettes.

调色板可能根据当前 GUI 样式改变在 QStyle::polish ().

警告: 不要将使用此函数结合 Qt 样式表 . When using style sheets, the palette of a widget can be customized using the "color", "background-color", "selection-color", "selection-background-color" and "alternate-background-color".

注意: Some styles do not use the palette for all drawing, for instance, if they make use of native theme engines. This is the case for the Windows Vista and macOS styles.

另请参阅 QWidget::setPalette (), palette (),和 QStyle::polish ().

[static] void QApplication:: setStyle ( QStyle * style )

将应用程序的 GUI 样式设为 style 。样式对象的所有权被转移给 QApplication ,因此 QApplication will delete the style object on application exit or when a new style is set and the old style is still the parent of the application object.



When switching application styles, the color palette is set back to the initial colors or the system defaults. This is necessary since certain styles have to adapt the color palette to be fully style-guide compliant.

Setting the style before a palette has been set, i.e., before creating QApplication , will cause the application to use QStyle::standardPalette () for the palette.

警告: Qt 样式表目前不支持自定义 QStyle 子类。计划在某些未来发行中解决这。

另请参阅 style (), QStyle , setPalette (),和 desktopSettingsAware ().

[static] QStyle *QApplication:: setStyle (const QString & style )


请求 QStyle 对象为 style QStyleFactory .

字符串必须是某一 QStyleFactory::keys (),通常是 windows、windowsvista、fusion 或 macos 之一。样式名不区分大小写。

返回 nullptr 若未知 style 被传递,否则 QStyle 返回对象被设为应用程序的 GUI 样式。

警告: 要确保应用程序样式设置正确,最好调用此函数先于 QApplication 构造函数,若可能的话。

[static] QStyle *QApplication:: style ()

另请参阅 setStyle () 和 QStyle .

[static] QWidget *QApplication:: topLevelAt (const QPoint & point )

返回的顶层 Widget 在给定 point ;返回 nullptr 若没有这样的 Widget。

[static] QWidget *QApplication:: topLevelAt ( int x , int y )


返回的顶层 Widget 在 point ( x , y );返回 0 若没有这种 Widget。

[static] QWidgetList QApplication:: topLevelWidgets ()

返回应用程序顶层 Widget (窗口) 的列表。

注意: 某些顶层 Widget 可能被隐藏,例如:工具提示,若目前未展示工具提示。


void showAllHiddenTopLevelWidgets()
    const QWidgetList topLevelWidgets = QApplication::topLevelWidgets();
    for (QWidget *widget : topLevelWidgets) {
        if (widget->isHidden())

另请参阅 allWidgets (), QWidget::isWindow (),和 QWidget::isHidden ().

[static] QWidget *QApplication:: widgetAt (const QPoint & point )

返回 Widget,在全局屏幕位置 point ,或 nullptr 若那里没有 Qt Widget。


另请参阅 QCursor::pos (), QWidget::grabMouse (),和 QWidget::grabKeyboard ().

[static] QWidget *QApplication:: widgetAt ( int x , int y )


返回 Widget,在全局屏幕位置 ( x , y ),或 nullptr 若那里没有 Qt Widget。



引用唯一应用程序对象的全局指针。它相当于 QCoreApplication::instance (),但铸造作为 QApplication 指针,因此才有效当唯一应用程序对象为 QApplication .

另请参阅 QCoreApplication::instance () 和 qGuiApp .