QGuiApplication 类

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QGuiApplication:: QGuiApplication ( 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 QGuiApplication object. In addition, argc must be greater than zero and argv must contain at least one valid character string.

The global 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 pixmaps, bitmaps etc.).

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

Supported Command Line Options

All Qt programs automatically support a set of command-line options that allow modifying the way Qt will interact with the windowing system. Some of the options are also accessible via environment variables, which are the preferred form if the application can launch GUI sub-processes or other applications (environment variables will be inherited by child processes). When in doubt, use the environment variables.

The options currently supported are the following:

• -platform platformName [:options] , specifies the Qt 平台抽象 (QPA) plugin.

  Overrides the QT_QPA_PLATFORM 环境变量。

• -platformpluginpath path , specifies the path to platform plugins.

  Overrides the QT_QPA_PLATFORM_PLUGIN_PATH 环境变量。

• -platformtheme platformTheme , specifies the platform theme.

  Overrides the QT_QPA_PLATFORMTHEME 环境变量。

• -plugin plugin , specifies additional plugins to load. The argument may appear multiple times.

  Concatenated with the plugins in the QT_QPA_GENERIC_PLUGINS 环境变量。

• -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.
• -qwindowgeometry geometry , specifies window geometry for the main window using the X11-syntax. For example: -qwindowgeometry 100x100+50+50
• -qwindowicon , sets the default window icon
• -qwindowtitle , sets the title of the first window
• -reverse , sets the application's layout direction to Qt::RightToLeft . This option is intended to aid debugging and should not be used in production. The default value is automatically detected from the user's locale (see also QLocale::textDirection ()).
• -session session , restores the application from an earlier session .

The following standard command line options are available for X11:

• -display hostname:screen_number , switches displays on X11.

  Overrides the DISPLAY 环境变量。

• -geometry geometry , same as -qwindowgeometry .

Platform-Specific Arguments

You can specify platform-specific arguments for the -platform option. Place them after the platform plugin name following a colon as a comma-separated list. For example, -platform windows:dialogs=xp,fontengine=freetype .

The following parameters are available for -platform windows :

• dialogs=[xp|none] , xp uses XP-style native dialogs and none disables them.
• fontengine=freetype , uses the FreeType font engine.
• menus=[native|none] , controls the use of native menus.

  Native menus are implemented using Win32 API and are simpler than QMenu -based menus in for example that they do allow for placing widgets on them or changing properties like fonts and do not provide hover signals. They are mainly intended for Qt Quick. By default, they will be used if the application is not an instance of QApplication or for Qt Quick Controls 2 applications.

• altgr , detect the key AltGr found on some keyboards as Qt::GroupSwitchModifier .

The following parameter is available for -platform cocoa (on macOS ):

• fontengine=freetype , uses the FreeType font engine.

For more information about the platform-specific arguments available for embedded Linux platforms, see Qt for Embedded Linux .

另请参阅 arguments () 和 QGuiApplication::platformName .

[virtual] QGuiApplication:: ~QGuiApplication ()

Destructs the application.

[static] QWindowList QGuiApplication:: allWindows ()

Returns a list of all the windows in the application.

The list is empty if there are no windows.

另请参阅 topLevelWindows ().

[static] Qt::ApplicationState QGuiApplication:: applicationState ()

Returns the current state of the application.

You can react to application state changes to perform actions such as stopping/resuming CPU-intensive tasks, freeing/loading resources or saving/restoring application data.

This function was introduced in Qt 5.2.

[signal] void QGuiApplication:: applicationStateChanged ( Qt::ApplicationState state )

此信号被发射当 state of the application changes.

This function was introduced in Qt 5.2.

另请参阅 applicationState ().

[static] void QGuiApplication:: changeOverrideCursor (const QCursor & cursor )

Changes the currently active application override cursor to cursor .

This function has no effect if setOverrideCursor () was not called.

另请参阅 setOverrideCursor (), overrideCursor (), restoreOverrideCursor ()，和 QWidget::setCursor ().

[static] QClipboard *QGuiApplication:: clipboard ()

Returns the object for interacting with the clipboard.

[signal] void QGuiApplication:: commitDataRequest ( QSessionManager & manager )

This signal deals with session management . It is emitted when the QSessionManager wants the application to commit all its data.

Usually this means saving all open files, after getting permission from the user. Furthermore you may want to provide a means by which the user can cancel the shutdown.

You should not exit the application within this signal. Instead, the session manager may or may not do this afterwards, depending on the context.

警告： Within this signal, no user interaction is possible, unless you ask the manager for explicit permission. See QSessionManager::allowsInteraction () 和 QSessionManager::allowsErrorInteraction () for details and example usage.

注意： 应使用 Qt::DirectConnection when connecting to this signal.

This function was introduced in Qt 4.2.

另请参阅 setFallbackSessionManagementEnabled (), isSessionRestored (), sessionId (), saveStateRequest ()，和 会话管理 .

[static] bool QGuiApplication:: desktopSettingsAware ()

返回 true if Qt is set to use the system's standard colors, fonts, etc.; otherwise returns false 。默认为 true .

另请参阅 setDesktopSettingsAware ().

qreal QGuiApplication:: devicePixelRatio () const

Returns the highest screen device pixel ratio found on the system. This is the ratio between physical pixels and device-independent pixels.

Use this function only when you don't know which window you are targeting. If you do know the target window, use QWindow::devicePixelRatio () 代替。

另请参阅 QWindow::devicePixelRatio ().

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

Reimplemented from QCoreApplication::event ().

[static] int QGuiApplication:: exec ()

进入主事件循环并等待，直到 exit () is called, and 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().

To make your application perform idle processing, e.g., 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被达成，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.

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

[static] QObject *QGuiApplication:: focusObject ()

返回 QObject in currently active window that will be final receiver of events tied to focus, such as key events.

[signal] void QGuiApplication:: focusObjectChanged ( QObject * focusObject )

This signal is emitted when final receiver of events tied to focus is changed. focusObject is the new receiver.

另请参阅 focusObject ().

[static] QWindow *QGuiApplication:: focusWindow ()

返回 QWindow that receives events tied to focus, such as key events.

[signal] void QGuiApplication:: focusWindowChanged ( QWindow * focusWindow )

This signal is emitted when the focused window changes. focusWindow is the new focused window.

另请参阅 focusWindow ().

[static] QFont QGuiApplication:: font ()

返回默认的应用程序字体。

另请参阅 setFont ().

[signal] void QGuiApplication:: fontChanged (const QFont & font )

此信号被发射当 font of the application changes.

This function was introduced in Qt 5.11.

另请参阅 font ().

[signal] void QGuiApplication:: fontDatabaseChanged ()

This signal is emitted when application fonts are loaded or removed.

另请参阅 QFontDatabase::addApplicationFont (), QFontDatabase::addApplicationFontFromData (), QFontDatabase::removeAllApplicationFonts ()，和 QFontDatabase::removeApplicationFont ().

[static] QInputMethod *QGuiApplication:: inputMethod ()

returns the input method.

The input method returns properties about the state and position of the virtual keyboard. It also provides information about the position of the current focused input element.

另请参阅 QInputMethod .

[static] bool QGuiApplication:: isFallbackSessionManagementEnabled ()

Returns whether QGuiApplication will use fallback session management.

默认为 true .

If this is true and the session manager allows user interaction, QGuiApplication will try to close toplevel windows after commitDataRequest () has been emitted. If a window cannot be closed, session shutdown will be canceled and the application will keep running.

Fallback session management only benefits applications that have an "are you sure you want to close this window?" feature or other logic that prevents closing a toplevel window depending on certain conditions, and that do nothing to explicitly implement session management. In applications that do implement session management using the proper session management API, fallback session management interferes and may break session management logic.

警告： If all windows are closed due to fallback session management and quitOnLastWindowClosed () 是 true , the application will quit before it is explicitly instructed to quit through the platform's session management protocol. That violation of protocol may prevent the platform session manager from saving application state.

This function was introduced in Qt 5.6.

另请参阅 setFallbackSessionManagementEnabled (), QSessionManager::allowsInteraction (), saveStateRequest (), commitDataRequest ()，和 会话管理 .

[static] bool QGuiApplication:: isLeftToRight ()

返回 true if the application's layout direction is Qt::LeftToRight ；否则返回 false .

另请参阅 layoutDirection () 和 isRightToLeft ().

[static] bool QGuiApplication:: isRightToLeft ()

返回 true if the application's layout direction is Qt::RightToLeft ；否则返回 false .

另请参阅 layoutDirection () 和 isLeftToRight ().

bool QGuiApplication:: isSavingSession () const

返回 true if the application is currently saving the session ；否则返回 false .

This is true when commitDataRequest () 和 saveStateRequest () are emitted, but also when the windows are closed afterwards by session management.

This function was introduced in Qt 5.0.

另请参阅 sessionId (), commitDataRequest ()，和 saveStateRequest ().

bool QGuiApplication:: isSessionRestored () const

返回 true if the application has been restored from an earlier session ；否则返回 false .

另请参阅 sessionId (), commitDataRequest ()，和 saveStateRequest ().

[static] Qt::KeyboardModifiers QGuiApplication:: keyboardModifiers ()

返回键盘修饰符键的当前状态。当前状态会被同步更新，当事件队列中的自发改变键盘状态的事件被清空时 ( QEvent::KeyPress and QEvent::KeyRelease 事件)。

应注意，这可能不反映调用时在输入设备上保持的实际键，而反映上述事件之一最后报告的修饰符。若没有被保持的键， Qt::NoModifier 被返回。

另请参阅 mouseButtons () 和 queryKeyboardModifiers ().

[signal] void QGuiApplication:: lastWindowClosed ()

This signal is emitted from exec () when the last visible primary window (i.e. window with no parent) is closed.

默认情况下， QGuiApplication quits after this signal is emitted. This feature can be turned off by setting quitOnLastWindowClosed to false .

另请参阅 QWindow::close () 和 QWindow::isTopLevel ().

[static] QWindow *QGuiApplication:: modalWindow ()

Returns the most recently shown modal window. If no modal windows are visible, this function returns zero.

A modal window is a window which has its modality property set to Qt::WindowModal or Qt::ApplicationModal . A modal window must be closed before the user can continue with other parts of the program.

Modal window are organized in a stack. This function returns the modal window at the top of the stack.

另请参阅 Qt::WindowModality and QWindow::setModality ().

[static] Qt::MouseButtons QGuiApplication:: mouseButtons ()

Returns the current state of the buttons on the mouse. The current state is updated synchronously as the event queue is emptied of events that will spontaneously change the mouse state ( QEvent::MouseButtonPress and QEvent::MouseButtonRelease 事件)。

It should be noted this may not reflect the actual buttons held on the input device at the time of calling but rather the mouse buttons as last reported in one of the above events. If no mouse buttons are being held Qt::NoButton 被返回。

另请参阅 keyboardModifiers ().

[override virtual] bool QGuiApplication:: notify ( QObject * object , QEvent * event )

Reimplemented from QCoreApplication::notify ().

[static] QCursor *QGuiApplication:: overrideCursor ()

返回活动应用程序的覆盖光标。

此函数返回 nullptr if no application cursor has been defined (i.e. the internal cursor stack is empty).

另请参阅 setOverrideCursor () 和 restoreOverrideCursor ().

[static] QPalette QGuiApplication:: palette ()

Returns the default application palette.

另请参阅 setPalette ().

[signal] void QGuiApplication:: paletteChanged (const QPalette & palette )

此信号被发射当 palette of the application changes.

This function was introduced in Qt 5.4.

另请参阅 palette ().

[static] QFunctionPointer QGuiApplication:: platformFunction (const QByteArray & function )

Returns a function pointer from the platformplugin matching function

[static] QPlatformNativeInterface *QGuiApplication:: platformNativeInterface ()

Returns the platform's native interface, for platform specific functionality.

[static] Qt::KeyboardModifiers QGuiApplication:: queryKeyboardModifiers ()

查询并返回键盘修饰符键的状态。不像 keyboardModifiers 此方法返回调用方法时保持在输入设备上的实际键。

它不依赖由此进程已接收的键按下事件，譬如：这使得当移动窗口时校验修饰符成为可能。注意：在大多数情况下，应使用 keyboardModifiers ()，其更快更准确，因为它包含的修饰符状态 (如同接收当前处理事件时状态)。

另请参阅 keyboardModifiers ().

[static] void QGuiApplication:: restoreOverrideCursor ()

撤消最后 setOverrideCursor ().

若 setOverrideCursor () has been called twice, calling restoreOverrideCursor() will activate the first cursor set. Calling this function a second time restores the original widgets' cursors.

另请参阅 setOverrideCursor () 和 overrideCursor ().

[signal] void QGuiApplication:: saveStateRequest ( QSessionManager & manager )

This signal deals with session management . It is invoked when the session manager wants the application to preserve its state for a future session.

For example, a text editor would create a temporary file that includes the current contents of its edit buffers, the location of the cursor and other aspects of the current editing session.

You should never exit the application within this signal. Instead, the session manager may or may not do this afterwards, depending on the context. Furthermore, most session managers will very likely request a saved state immediately after the application has been started. This permits the session manager to learn about the application's restart policy.

警告： Within this signal, no user interaction is possible, unless you ask the manager for explicit permission. See QSessionManager::allowsInteraction () 和 QSessionManager::allowsErrorInteraction () 了解细节。

注意： 应使用 Qt::DirectConnection when connecting to this signal.

This function was introduced in Qt 4.2.

另请参阅 isSessionRestored (), sessionId (), commitDataRequest ()，和 会话管理 .

[signal] void QGuiApplication:: screenAdded ( QScreen * screen )

This signal is emitted whenever a new screen screen has been added to the system.

另请参阅 screens (), primaryScreen ，和 screenRemoved ().

[static] QScreen *QGuiApplication:: screenAt (const QPoint & point )

返回屏幕，位于 point ，或 nullptr 若在任何屏幕之外。

point is in relation to the virtualGeometry() of each set of virtual siblings. If the point maps to more than one set of virtual siblings the first match is returned.

This function was introduced in Qt 5.10.

[signal] void QGuiApplication:: screenRemoved ( QScreen * screen )

This signal is emitted whenever a screen is removed from the system. It provides an opportunity to manage the windows on the screen before Qt falls back to moving them to the primary screen.

This function was introduced in Qt 5.4.

另请参阅 screens (), screenAdded (), QObject::destroyed ()，和 QWindow::setScreen ().

[static] QList < QScreen *> QGuiApplication:: screens ()

Returns a list of all the screens associated with the windowing system the application is connected to.

QString QGuiApplication:: sessionId () const

返回当前 session's 标识符。

If the application has been restored from an earlier session, this identifier is the same as it was in that previous session. The session identifier is guaranteed to be unique both for different applications and for different instances of the same application.

另请参阅 isSessionRestored (), sessionKey (), commitDataRequest ()，和 saveStateRequest ().

QString QGuiApplication:: sessionKey () const

返回会话键，在当前 session .

If the application has been restored from an earlier session, this key is the same as it was when the previous session ended.

The session key changes every time the session is saved. If the shutdown process is cancelled, another session key will be used when shutting down again.

另请参阅 isSessionRestored (), sessionId (), commitDataRequest ()，和 saveStateRequest ().

[static] void QGuiApplication:: setDesktopSettingsAware ( bool on )

Sets whether Qt should use the system's standard colors, fonts, etc., to on . By default, this is true .

此函数必须先被调用，才能创建 QGuiApplication 对象，像这样：

int main(int argc, char *argv[])
{
    QApplication::setDesktopSettingsAware(false);
    QApplication app(argc, argv);
    ...
    return app.exec();
}
							

另请参阅 desktopSettingsAware ().

[static] void QGuiApplication:: setFallbackSessionManagementEnabled ( bool enabled )

Sets whether QGuiApplication will use fallback session management to enabled .

This function was introduced in Qt 5.6.

另请参阅 isFallbackSessionManagementEnabled ().

[static] void QGuiApplication:: setFont (const QFont & font )

把默认应用程序字体改为 font .

另请参阅 font ().

[static] void QGuiApplication:: setOverrideCursor (const QCursor & cursor )

Sets the application override cursor to cursor .

Application override cursors are intended for showing the user that the application is in a special state, for example during an operation that might take some time.

This cursor will be displayed in all the application's widgets until restoreOverrideCursor () or another setOverrideCursor() is called.

Application cursors are stored on an internal stack. setOverrideCursor() pushes the cursor onto the stack, and restoreOverrideCursor () pops the active cursor off the stack. changeOverrideCursor () changes the curently active application override cursor.

Every setOverrideCursor() must eventually be followed by a corresponding restoreOverrideCursor (), otherwise the stack will never be emptied.

范例：

QApplication::setOverrideCursor(QCursor(Qt::WaitCursor));
calculateHugeMandelbrot();              // lunch time...
QApplication::restoreOverrideCursor();
							

另请参阅 overrideCursor (), restoreOverrideCursor (), changeOverrideCursor ()，和 QWidget::setCursor ().

[static] void QGuiApplication:: setPalette (const QPalette & pal )

Changes the default application palette to pal .

另请参阅 palette ().

[static] QStyleHints *QGuiApplication:: styleHints ()

Returns the application's style hints.

The style hints encapsulate a set of platform dependent properties such as double click intervals, full width selection and others.

The hints can be used to integrate tighter with the underlying platform.

另请参阅 QStyleHints .

[static] void QGuiApplication:: sync ()

Function that can be used to sync Qt state with the Window Systems state.

This function will first empty Qts events by calling QCoreApplication::processEvents (), then the platform plugin will sync up with the windowsystem, and finally Qts events will be delived by another call to QCoreApplication::processEvents ();

This function is timeconsuming and its use is discouraged.

This function was introduced in Qt 5.2.

[static] QWindow *QGuiApplication:: topLevelAt (const QPoint & pos )

Returns the top level window at the given position pos , if any.

[static] QWindowList QGuiApplication:: topLevelWindows ()

返回应用程序顶层窗口列表。

另请参阅 allWindows ().