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QApplication Class Reference


The QApplication class manages the GUI application's control flow and main settings. More...

#include <qapplication.h>

Inherits QObject.

Inherited by QXtApplication.

List of all member functions.

Public Members

Public Slots

Signals

Static Public Members

Related Functions

(Note that these are not member functions.)

Detailed Description

The QApplication class manages the GUI application's control flow and main settings.

It contains the main event loop, where all events from the window system and other sources are processed and dispatched. It also handles the application initialization and finalization, and provides session management. Finally, it handles most system-wide and application-wide settings.

For any GUI application that uses Qt, there is precisely one QApplication object, no matter whether the application has 0, 1, 2 or even more windows at the moment.

This object (you can access is using the global variable qApp) does a great many things, most importantly:

The Application walktrough example contains a typical complete main() that does the usual things with QApplication.

Since the QApplication object does so much initialization, it is absolutely necessary to create it before any other objects related to the user interface are created.

Since it also deals with common command line arguments, it is usually a good idea to create it before any interpretation or modification of argv is done in the application itself. (Note also that for X11, setMainWidget() may change the main widget according to the -geometry option. To preserve this functionality, you must set your defaults before setMainWidget() and any overrides after.)

Groups of functions:

Non-GUI programs
While Qt is not optimized or designed for writing non-GUI programs, it's possible to use some of its classes without creating a QApplication. This can be useful if you wish to share code between a non-GUI server and a GUI client.

Examples: qdir/qdir.cpp showimg/main.cpp rangecontrols/main.cpp validator/main.cpp themes/main.cpp listviews/main.cpp aclock/main.cpp checklists/main.cpp buttons_groups/main.cpp drawlines/connect.cpp dclock/main.cpp wizard/main.cpp xform/xform.cpp application/main.cpp qiconview/main.cpp cursor/cursor.cpp layout/layout.cpp life/main.cpp i18n/main.cpp drawdemo/drawdemo.cpp lineedits/main.cpp popup/popup.cpp listbox/main.cpp menu/menu.cpp progress/progress.cpp scribble/main.cpp qmag/qmag.cpp table/main.cpp splitter/splitter.cpp progressbar/main.cpp richtext/main.cpp tooltip/main.cpp qwerty/main.cpp forever/forever.cpp rot13/rot13.cpp desktop/desktop.cpp scrollview/scrollview.cpp qfd/qfd.cpp addressbook/main.cpp movies/main.cpp picture/picture.cpp listbox_combo/main.cpp hello/main.cpp qfileiconview/main.cpp qbrowser/main.cpp biff/main.cpp tictac/main.cpp customlayout/main.cpp dirview/main.cpp


Member Function Documentation

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

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

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 (includes widgets, pixmaps, bitmaps etc.)

Notice that argc and argv might be changed. Qt removes command line arguments that it recognizes. argc and argv are can be accessed later by qApp->argc() and qApp->argv(). The documentation for argv() contains a detailed description of how to process command line arguments.

Qt debugging options (not available if Qt was compiled with the NO_DEBUG flag defined):

See Debugging Techniques for a more detailed explanation.

All Qt programs automatically support the following command line options:

The X11 version of Qt also supports some traditional X11 command line options:

See also: argc() and argv().

QApplication::~QApplication() [virtual]

Cleans up any window system resources that were allocated by this application. Sets the global variable qApp to null. Unlike former versions of Qt the destructor does not delete all remaining widgets.

voidQApplication::aboutToQuit() [signal]

This signal is emitted when the application is about to quit the main event loop. This may happen either after a call to quit() from inside the applicaton or when the users shuts down the entire desktop session.

The signal is particularly useful if your application has to do some last-second cleanups. Note that no user interaction is possible at this state.

See also: quit().

QWidget*QApplication::activeModalWidget() [static]

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 to TRUE. A modal widget must be finished before the user can continue with other parts of the program.

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

See also: currentPopupWidget() and topLevelWidgets().

QWidget*QApplication::activePopupWidget() [static]

Returns the active popup widget.

A popup widget is a special top level widget that sets the WType_Popup widget flag, e.g. the QPopupMenu widget. When the application opens a popup widget, all events are sent to the popup and 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 on top of the stack.

See also: currentModalWidget() and topLevelWidgets().

QWidget*QApplication::activeWindow()const

Returns the application toplevel window that has the keyboard input focus, or null if no application window has the focus. Note that there might be an activeWindow even if there is no focusWidget, if no widget in that window accepts key events.

See also: QWidget::setFocus(), QWidget::hasFocus() and focusWidget().

QWidgetList*QApplication::allWidgets() [static]

Returns a list of all the widgets in the application.

The list is created using new and must be deleted by the caller.

The list is empty if there are no widgets.

Note that some of the widgets may be hidden.

Example:

    //
    // Updates all widgets.
    //
    QWidgetList  *list = QApplication::allWidgets();
    QWidgetListIt it( *list );          // iterate over the widgets
    while ( it.current() ) {            // for each top level widget...
        it.current()->update();
        ++it;
    }
    delete list;                        // delete the list, not the widgets

The QWidgetList class is defined in the qwidcoll.h header file.

Warning: Delete the list away as soon you have finished using it. You can get in serious trouble if you for instance try to access a widget that has been deleted.

See also: topLevelWidgets(), QWidget::isVisible() and QList::isEmpty(),.

intQApplication::argc()const

Returns the number of command line arguments.

The documentation for argv() contains a detailed description of how to process command line arguments.

See also: argv() and QApplication::QApplication().

char**QApplication::argv()const

Returns the command line argument vector.

argv()[0] is the program name, argv()[1] is the first argument and argv()[argc()-1] is the last argument.

A QApplication object is constructed by passing argc and argv from the main() function. Some of the arguments may be recognized as Qt options removed from the argument vector. For example, the X11 version of Qt knows about -display, -font and a few more options.

Example:

    // showargs.cpp - displays program arguments in a list box

    #include <qapplication.h>
    #include <qlistbox.h>

    int main( int argc, char **argv )
    {
        QApplication a( argc, argv );
        QListBox b;
        a.setMainWidget( &b );
        for ( int i=0; i<a.argc(); i++ )        // a.argc() == argc
            b.insertItem( a.argv()[i] );        // a.argv()[i] == argv[i]
        b.show();
        return a.exec();
    }

If you run showargs -display unix:0 -font 9x15bold hello world under X11, the list box contains the three strings "showargs", "hello" and "world".

See also: argc() and QApplication::QApplication().

voidQApplication::beep() [static]

Sounds the bell, using the default volume and sound.

QClipboard*QApplication::clipboard() [static]

Returns a pointer to the application global clipboard.

voidQApplication::closeAllWindows() [slot]

A convenience function that closes all toplevel windows.

The function is particularly useful for applications with many toplevel windows. It could for example be connected to a "Quit" entry in the file menu as shown in the following code example:

    // the "Quit" menu entry should try to close all windows
    QPopupMenu* file = new QPopupMenu( this );
    file->insertItem( tr("&Quit"), qApp, SLOT(closeAllWindows()), CTRL+Key_Q );

    // when the last window was closed, the application should quit
    connect( qApp, SIGNAL( lastWindowClosed() ), qApp, SLOT( quit() ) );

The windows are closed in random order, until one window does not accept the close event.

See also: QWidget::close(), QWidget::closeEvent(), lastWindowClosed(), quit(), topLevelWidgets() and QWidget::isTopLevel().

boolQApplication::closingDown() [static]

Returns TRUE if the application objects are being destroyed.

See also: startingUp().

intQApplication::colorSpec() [static]

Returns the color specification.

See also: QApplication::setColorSpec().

voidQApplication::commitData(QSessionManager&sm) [virtual]

This function deals with session management. It is invoked when the session manager wants the application to commit all its data.

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

Note that you should not exit the application within this function. Instead, the session manager may or may not do this afterwards, depending on the context.

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

Details about session management in general can be found here.

See also: isSessionRestored(), sessionId() and saveState().

intQApplication::cursorFlashTime() [static]

Returns the text cursor's flash time in milliseconds. The flash time is the time requried to display, invert and restore the caret display.

The default value is 1000 milliseconds. Under Windows, the control panel value is used.

Widgets should not cache this value since it may vary any time the user changes the global desktop settings.

See also: setCursorFlashTime().

QTextCodec*QApplication::defaultCodec()const

Returns the default codec (see setDefaultCodec()). Returns 0 by default (no codec).

QWidget*QApplication::desktop() [static]

Returns the desktop widget (also called the root window).

The desktop widget is useful for obtaining the size of the screen. It can also be used to draw on the desktop.

    QWidget *d = QApplication::desktop();
    int w=d->width();                   // returns screen width
    int h=d->height();                  // returns screen height
    d->setBackgroundColor( red );       // makes desktop red

Examples: qmag/qmag.cpp

boolQApplication::desktopSettingsAware() [static]

Returns the value set by setDesktopSettingsAware(), by default TRUE.

See also: setDesktopSettingsAware().

intQApplication::doubleClickInterval() [static]

Returns the maximum duration for a double click.

The default value is 400 milliseconds. Under Windows, the control panel value is used.

See also: setDoubleClickInterval().

intQApplication::enter_loop()

This function enters the main event loop (recursively). Do not call it unless you really know what you are doing.

See also: exit_loop().

intQApplication::exec()

Enters the main event loop and waits until exit() is called or the main widget is destroyed. Returns the value that was specified to exit(), which is 0 if exit() is called via quit().

It is necessary to call this function to start event handling. The main event loop receives events from the window system and dispatches these to the application widgets.

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 widget have 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 with 0 timeout. More advanced idle processing schemes can be achieved by using processEvents() and processOneEvent().

See also: quit(), exit(), processEvents() and setMainWidget().

Examples: showimg/main.cpp rangecontrols/main.cpp validator/main.cpp themes/main.cpp listviews/main.cpp aclock/main.cpp checklists/main.cpp buttons_groups/main.cpp drawlines/connect.cpp dclock/main.cpp mainlyQt/editor.cpp xform/xform.cpp application/main.cpp qiconview/main.cpp cursor/cursor.cpp layout/layout.cpp life/main.cpp i18n/main.cpp drawdemo/drawdemo.cpp lineedits/main.cpp popup/popup.cpp listbox/main.cpp menu/menu.cpp progress/progress.cpp scribble/main.cpp qmag/qmag.cpp table/main.cpp splitter/splitter.cpp progressbar/main.cpp richtext/main.cpp tooltip/main.cpp qwerty/main.cpp forever/forever.cpp rot13/rot13.cpp scrollview/scrollview.cpp qfd/qfd.cpp addressbook/main.cpp movies/main.cpp picture/picture.cpp listbox_combo/main.cpp hello/main.cpp qfileiconview/main.cpp qbrowser/main.cpp biff/main.cpp tictac/main.cpp customlayout/main.cpp dirview/main.cpp

voidQApplication::exit(intretcode=0) [static]

Tells the application to exit with a return code.

After this function has been called, the application leaves the main event loop and returns from the call to exec(). The exec() function returns retcode.

By convention, retcode 0 means success, any non-zero value indicates an error.

Note that unlike the C library exit function, this function does returns to the caller - it is event processing that stops.

See also: quit() and exec().

Examples: picture/picture.cpp

voidQApplication::exit_loop()

This function leaves from a recursive call to the main event loop. Do not call it unless you are an expert.

See also: enter_loop().

voidQApplication::flushX() [static]

Flushes the X event queue in the X11 implementation. Does nothing on other platforms.

See also: syncX().

QWidget*QApplication::focusWidget()const

Returns the application widget that has the keyboard input focus, or null if no application widget has the focus.

See also: QWidget::setFocus(), QWidget::hasFocus() and activeWindow().

QFontQApplication::font(constQWidget*w=0) [static]

Returns the default font for a widget. Basically this function uses the class name of the widget to get a font for it.

If w is 0 the default application font is returned.

See also: setFont(), fontMetrics() and QWidget::font().

QFontMetricsQApplication::fontMetrics() [static]

Returns display (screen) font metrics for the application font.

See also: font(), setFont(), QWidget::fontMetrics() and QPainter::fontMetrics().

boolQApplication::hasGlobalMouseTracking() [static]

Returns TRUE if global mouse tracking is enabled, otherwise FALSE.

See also: setGlobalMouseTracking().

voidQApplication::installTranslator(QTranslator*mf)

Adds mf to the list of message files to be used for localization. Message files are searched starting with the most recently added file.

See also: removeTranslator(), translate() and QObject::tr().

Examples: i18n/main.cpp

boolQApplication::isSessionRestored()const

Returns whether the application has been restored from an earlier session.

See also: sessionId(), commitData() and saveState().

voidQApplication::lastWindowClosed() [signal]

This signal is emitted when the user has closed the last remaining top level window.

The signal is very useful when your application has many top level widgets but no main widget. You can then connect it to the quit() slot.

For convenience, transient toplevel widgets such as popup menus and dialogs are omitted.

See also: mainWidget(), topLevelWidgets(), QWidget::isTopLevel() and QWidget::close().

intQApplication::loopLevel()const

Returns the current loop level

See also: enter_loop() and exit_loop().

QWidget*QApplication::mainWidget()const

Returns the main application widget, or 0 if there is not a defined main widget.

See also: setMainWidget().

boolQApplication::notify(QObject*receiver, QEvent*event) [virtual]

Sends event to receiver: receiver->event( event ) Returns the value that is returned from the receiver's event handler.

Reimplementing this virtual function is one of five ways to process an event:

  1. Reimplementing this function. Very powerful, you get complete control, but of course only one subclass can be qApp.

  2. Installing an event filter on qApp. Such an event filter gets to process all events for all widgets, so it's just as powerful as reimplementing notify(), and in this way it's possible to have more than one application-global event filter. Global event filter get to see even mouse events for disabled widgets, and if global mouse tracking is enabled, mouse move events for all widgets.

  3. Reimplementing QObject::event() (as QWidget does). If you do this you get tab key-presses, and you get to see the events before any widget-specific event filters.

  4. Installing an event filter on the object. Such an even filter gets all the events except Tab and Shift-Tab key presses.

  5. Finally, reimplementing paintEvent(), mousePressEvent() and so on. This is the normal, easiest and least powerful way.

See also: QObject::event() and installEventFilter().

QCursor*QApplication::overrideCursor() [static]

Returns the active application override cursor.

This function returns 0 if no application cursor has been defined (i.e. the internal cursor stack is empty).

See also: setOverrideCursor() and restoreOverrideCursor().

QPaletteQApplication::palette(constQWidget*w=0) [static]

Returns a pointer to the default application palette. There is always an application palette, i.e. the returned pointer is guaranteed to be non-null.

If a widget is passed as argument, the default palette for the widget's class is returned. This may or may not be the application palette, but in most cases there won't be a special palette for certain types of widgets. An exception is the popup menu under Windows, when the user defined a special background color for menus in the display settings.

See also: setPalette() and QWidget::palette().

voidQApplication::polish(QWidget*w) [virtual]

Polishing of widgets.

Usually widgets call this automatically when they are polished. It may be used to do some style-based central customization of widgets.

Note that you are not limited to public functions of QWidget. Instead, based on meta information like QObject::className() you are able to customize any kind of widgets.

The default implementation sets a class specific font or palette if available and no font or palette has been set yet. Then it calls QStyle::polish().

See also: QStyle::polish(), QWidget::polish(), setPalette() and setFont().

voidQApplication::postEvent(QObject*receiver, QEvent*event) [static]

Stores the event in a queue and returns immediately.

The event must be allocated on the heap, as it is deleted when the event has been posted.

When control returns to the main event loop, all events that are stored in the queue will be sent using the notify() function.

See also: sendEvent().

voidQApplication::processEvents()

Processes pending events, for 3 seconds or until there are no more events to process, then return.

You can call this function occasionally when your program is busy doing a long operation (e.g. copying a file).

See also: processOneEvent(), exec() and QTimer.

voidQApplication::processEvents(intmaxtime)

Processes pending events, for maxtime milliseconds or until there are no more events to process, then return.

You can call this function occasionally when you program is busy doing a long operation (e.g. copying a file).

See also: processOneEvent(), exec() and QTimer.

voidQApplication::processOneEvent()

Waits for an event to occur, processes it, then returns.

This function is useful for adapting Qt to situations where the event processing must be grafted into existing program loops. Beware that using this function in new applications may be an indication of design problems.

See also: processEvents(), exec() and QTimer.

voidQApplication::quit() [slot]

Tells the application to exit with return code 0 (success). Equivalent to calling QApplication::exit( 0 ).

This function is a slot, i.e. you may connect any signal to activate quit().

Example:

    QPushButton *quitButton = new QPushButton( "Quit" );
    connect( quitButton, SIGNAL(clicked()), qApp, SLOT(quit()) );

See also: exit() and aboutToQuit().

voidQApplication::removePostedEvents(QObject*receiver) [static]

Removes all events posted using postEvent() for receiver.

The events are not dispatched, simply removed from the queue. You should never need to call this function.

voidQApplication::removeTranslator(QTranslator*mf)

Removes mf from the list of message files used by this application. Does not, of course, delete mf.

See also: installTranslator(), translate() and QObject::tr().

voidQApplication::restoreOverrideCursor() [static]

Restores the effect of setOverrideCursor().

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

Application cursors are stored on an internal stack. setOverrideCursor() pushes the cursor onto the stack, and restoreOverrideCursor() pops the active cursor off the stack. Every setOverrideCursor() must have an corresponding restoreOverrideCursor(), otherwise the stack will get out of sync. overrideCursor() returns 0 if the cursor stack is empty.

See also: setOverrideCursor() and overrideCursor().

voidQApplication::saveState(QSessionManager&sm) [virtual]

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

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

Note that you should never exit the application within this function. Instead, the session manager may or may not do this afterwards, depending on the context. Futhermore, 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.

Important
Within this function, no user interaction is possible, unless you ask the session manager sm for explicit permission. See QSessionManager::allowsInteraction() and QSessionManager::allowsErrorInteraction() for details.

Details about session management in general can be found here

See also: isSessionRestored(), sessionId() and commitData().

boolQApplication::sendEvent(QObject*receiver, QEvent*event) [static]

Sends an event directly to a receiver, using the notify() function. Returns the value that was returned from the event handler.

See also: postEvent() and notify().

Examples: popup/popup.cpp

voidQApplication::sendPostedEvents() [static]

Dispatches all posted events.

voidQApplication::sendPostedEvents(QObject*receiver, intevent_type) [static]

Immediately dispatches all events which have been previously enqueued with QApplication::postEvent() and which are for the object receiver and have the event_type.

If receiver is 0, all objects get their events. If event_type is 0, all types of events are dispatched.

Some event compression may occur. Note that events from the window system are not dispatched by this function.

QStringQApplication::sessionId()const

Returns the identifier of the current session.

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 for both different applications and different instances of the same application.

See also: isSessionRestored(), commitData() and saveState().

voidQApplication::setColorSpec(intspec) [static]

Sets the color specification for the application to spec.

The color specification controls how your application allocates colors. You must set the color specification before you create the QApplication object.

The choices are:

Example:

  int main( int argc, char **argv )
  {
      QApplication::setColorSpec( QApplication::ManyColor );
      QApplication a( argc, argv );
      ...
  }

QColor provides more functionality for controlling color allocation and freeing up certain colors. See QColor::enterAllocContext() for more information.

To see what mode you end up with, you can call QColor::numBitPlanes() once the QApplication object exists. A value greater than 8 (typically 16, 24 or 32) means true color.

The color cube used by Qt are all those colors with red, green, and blue components of either 0x00, 0x33, 0x66, 0x99, 0xCC, or 0xFF.

See also: colorSpec(), QColor::numBitPlanes() and QColor::enterAllocContext().

Examples: showimg/main.cpp themes/main.cpp tetrix/tetrix.cpp qbrowser/main.cpp

voidQApplication::setCursorFlashTime(intmsecs) [static]

Sets the text cursor's flash time to msecs milliseconds. The flash time is the time requried to display, invert and restore the caret display: A full flash cycle. Usually, the text cursor is displayed for msecs/2 millisecnds, then hidden for msecs/2 milliseconds.

Under windows, calling this function sets the double click interval for all windows.

See also: cursorFlashTime().

voidQApplication::setDefaultCodec(QTextCodec*codec)

If the literal quoted text in the program is not in the Latin1 encoding, this function can be used to set the appropriate encoding. For example, software developed by Korean programmers might use eucKR for all the text in the program, in which case main() would be:

    main(int argc, char** argv)
    {
        QApplication app(argc, argv);
        ... install any additional codecs ...
        app.setDefaultCodec( QTextCodec::codecForName("eucKR") );
        ...
    }

Note that this is not the way to select the encoding that the user has chosen. For example, to convert an application containing literal English strings to Korean, all that is needed is for the English strings to be passed through tr() and for translation files to be loaded. For details of internationalization, see the Qt Internationalization documentation.

Note also that some Qt built-in classes call tr() with various strings. These strings are in English, so for a full translation, a codec would be required for these strings.

voidQApplication::setDesktopSettingsAware(boolon) [static]

By default, Qt will try to get the current standard colors, fonts etc. from the underlying window system's desktop settings (resources), and use them for all relevant widgets. This behavior can be switched off by calling this function with on set to FALSE.

This static function must be called before creating the QApplication object, like this:

  int main( int argc, char** argv ) {
    QApplication::setDesktopSettingsAware( FALSE ); // I know better than the user
    QApplication myApp( argc, argv );           // gimme default fonts & colors
    ...
  }

See also: desktopSettingsAware().

voidQApplication::setDoubleClickInterval(intms) [static]

Sets the time limit that distinguishes a double click from two consecutive mouse clicks to ms milliseconds.

Under windows, calling this function sets the double click interval for all windows.

See also: doubleClickInterval().

voidQApplication::setFont(constQFont&font, boolupdateAllWidgets=FALSE, constchar*className=0) [static]

Changes the default application font to font.

The default font depends on the underlying window system, under X Windows on the X server in use.

If updateAllWidgets is TRUE, then the font of all existing widgets is set to font.

If a className is passed, then the font is only set for widgets that inherit this class in the sense of QObject::inherits()

Widgets created after this call get font as their font when they access it.

See also: font(), fontMetrics() and QWidget::setFont().

Examples: showimg/main.cpp desktop/desktop.cpp

voidQApplication::setGlobalMouseTracking(boolenable) [static]

Enables global mouse tracking if enable is TRUE or disables it if enable is FALSE.

Enabling global mouse tracking makes it possible for widget event filters or application event filters to get all mouse move events, even when no button is depressed. This is useful for special GUI elements, e.g. tool tips.

Global mouse tracking does not affect widgets and their mouseMoveEvent(). For a widget to get mouse move events when no button is depressed, it must do QWidget::setMouseTracking(TRUE).

This function has an internal counter. Each setGlobalMouseTracking(TRUE) must have a corresponding setGlobalMouseTracking(FALSE).

See also: hasGlobalMouseTracking() and QWidget::hasMouseTracking().

voidQApplication::setMainWidget(QWidget*mainWidget) [virtual]

Sets the main widget of the application.

The special thing about the main widget is that destroying the main widget (i.e. the program calls QWidget::close() or the user double-clicks the window close box) will leave the main event loop and exit the application.

For X11, this function also resizes and moves the main widget according to the -geometry command-line option, so you should set the default geometry before calling setMainWidget().

See also: mainWidget(), exec() and quit().

Examples: rangecontrols/main.cpp validator/main.cpp themes/main.cpp listviews/main.cpp aclock/main.cpp checklists/main.cpp buttons_groups/main.cpp drawlines/connect.cpp dclock/main.cpp mainlyQt/editor.cpp xform/xform.cpp qiconview/main.cpp cursor/cursor.cpp layout/layout.cpp life/main.cpp i18n/main.cpp drawdemo/drawdemo.cpp lineedits/main.cpp popup/popup.cpp listbox/main.cpp menu/menu.cpp progress/progress.cpp scribble/main.cpp qmag/qmag.cpp table/main.cpp splitter/splitter.cpp progressbar/main.cpp richtext/main.cpp tooltip/main.cpp forever/forever.cpp rot13/rot13.cpp qfd/qfd.cpp addressbook/main.cpp picture/picture.cpp listbox_combo/main.cpp hello/main.cpp qfileiconview/main.cpp biff/main.cpp tictac/main.cpp customlayout/main.cpp dirview/main.cpp

voidQApplication::setOverrideCursor(constQCursor&cursor, boolreplace=FALSE) [static]

Sets the application override cursor to cursor.

Application override cursor 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 application 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. Every setOverrideCursor() must have an corresponding restoreOverrideCursor(), otherwise the stack will get out of sync. overrideCursor() returns 0 if the cursor stack is empty.

If replace is TRUE, the new cursor will replace the last override cursor.

Example:

    QApplication::setOverrideCursor( waitCursor );
    calculateHugeMandelbrot();                  // lunch time...
    QApplication::restoreOverrideCursor();

See also: overrideCursor(), restoreOverrideCursor() and QWidget::setCursor().

voidQApplication::setPalette(constQPalette&palette, boolupdateAllWidgets=FALSE, constchar*className=0) [static]

Changes the default application palette to palette.

If updateAllWidgets is TRUE, then the palette of all existing widgets is set to palette.

If a className is passed, then the palette is only set for widgets that inherit this class in the sense of QObject::inherits()

Widgets created after this call get palette as their palette when they access it.

The palette may be changed according to the current GUI style in QStyle::polish().

See also: QWidget::setPalette(), palette() and QStyle::polish().

voidQApplication::setStyle(QStyle*style) [static]

Sets the application GUI style to style.

See also: style() and QStyle.

Examples: themes/main.cpp

voidQApplication::setWinStyleHighlightColor(constQColor&c) [static]

This function is obsolete. It is provided to keep old programs working. We strongly advise against using it in new code.

Sets the color used to mark selections in windows style for all widgets in the application. Will repaint all widgets if the color is changed.

The default color is darkBlue.

See also: winStyleHighlightColor().

boolQApplication::startingUp() [static]

Returns TRUE if an application object has not been created yet.

See also: closingDown().

QStyle&QApplication::style() [static]

Returns the style object of the application.

See also: setStyle() and QStyle.

voidQApplication::syncX() [static]

Synchronizes with the X server in the X11 implementation. Does nothing on other platforms.

See also: flushX().

QWidgetList*QApplication::topLevelWidgets() [static]

Returns a list of the top level widgets in the application.

The list is created using new and must be deleted by the caller.

The list is empty if there are no top level widgets.

Note that some of the top level widgets may be hidden, for example all the popup menus of a menubar.

Example:

    //
    // Shows all hidden top level widgets.
    //
    QWidgetList  *list = QApplication::topLevelWidgets();
    QWidgetListIt it( *list );          // iterate over the widgets
    while ( it.current() ) {            // for each top level widget...
        if ( !it.current()->isVisible() )
            it.current()->show();
        ++it;
    }
    delete list;                        // delete the list, not the widgets

The QWidgetList class is defined in the qwidcoll.h header file.

Warning: Delete the list away as soon you have finished using it. You can get in serious trouble if you for instance try to access a widget that has been deleted.

See also: allWidgets(), QWidget::isTopLevel(), QWidget::isVisible() and QList::isEmpty().

QStringQApplication::translate(constchar*scope, constchar*key)const

Returns the best available translation for key in scope, by querying the installed messages files. The message file that was installed last is asked first.

QObject::tr() offers a more convenient way to use this functionality.

scope is typically a class name (e.g. MyDialog) and is either English text or a short marker text, if the output text will be very long (as for help texts).

If none of the message files contain a translation for key in scope, this function returns key.

This function is not virtual, but you can add alternative translation techniques by installing subclasses of QTranslator.

See also: QObject::tr(), installTranslator(), removeTranslator() and QTranslator.

QWidget*QApplication::widgetAt(intx, inty, boolchild=FALSE) [static]

Returns a pointer to the widget at global screen position (x,y), or a null pointer if there is no Qt widget there.

If child is FALSE and there is a child widget at position (x,y), the top-level widget containing it is returned. If child is TRUE the child widget at position (x,y) is returned.

See also: QCursor::pos(), QWidget::grabMouse() and QWidget::grabKeyboard().

QWidget*QApplication::widgetAt(constQPoint&pos, boolchild=FALSE) [static]

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

constQColor&QApplication::winStyleHighlightColor() [static]

This function is obsolete. It is provided to keep old programs working. We strongly advise against using it in new code.

Returns the color used to mark selections in windows style.

See also: setWinStyleHighlightColor().


Related Functions

void CHECK_PTR (void * p)

If p is null, a fatal messages says that the program ran out of memory and exits. If p is not null, nothing happens.

This is really a macro defined in qglobal.h.

Example:

    int *a;
    CHECK_PTR( a = new int[80] );       // never do this!
      // do this instead:
    a = new int[80];
    CHECK_PTR( a );                     // this is fine

See also: fatal() and Debugging

Q_EXPORT void qWarning (const char * msg, ...)

Prints a warning message, or calls the message handler (if it has been installed).

This function takes a format string and a list of arguments, similar to the C printf() function.

Example:

    void f( int c )
    {
        if ( c > 200 )
            qWarning( "f: bad argument, c == %d", c );
    }

Under X11, the text is printed to stderr. Under Windows, the text is sent to the debugger.

Warning: The internal buffer is limited to 512 bytes (including the 0-terminator).

See also: debug(), fatal(), qInstallMsgHandler() and Debugging

Examples: progress/progress.cpp tictac/main.cpp

void ASSERT (bool test)

Prints a warning message containing the source code file name and line number if test is FALSE.

This is really a macro defined in qglobal.h.

ASSERT is useful for testing required conditions in your program.

Example:

    //
    // File: div.cpp
    //

    #include <qglobal.h>

    int divide( int a, int b )
    {
        ASSERT( b != 0 );                       // this is line 9
        return a/b;
    }

If b is zero, the ASSERT statement will output the following message using the warning() function:

    ASSERT: "b == 0" in div.cpp (9)

See also: warning() and Debugging

Q_EXPORT bool qSysInfo (int * wordSize, bool * bigEndian)

Obtains information about the system.

The system's word size in bits (typically 32) is returned in *wordSize. The *bigEndian is set to TRUE if this is a big-endian machine, or to FALSE if this is a little-endian machine.

This function calls fatal() with a message if the computer is truly weird (i.e. different endianness for 16 bit and 32 bit integers).

Q_EXPORT msg_handler qInstallMsgHandler (msg_handler h)

Installs a Qt message handler. Returns a pointer to the message handler previously defined.

The message handler is a function that prints out debug messages, warnings and fatal error messages. The Qt library (debug version) contains hundreds of warning messages that are printed when internal errors (usually invalid function arguments) occur. If you implement your own message handler, you get total control of these messages.

The default message handler prints the message to the standard output under X11 or to the debugger under Windows. If it is a fatal message, the application aborts immediately.

Only one message handler can be defined, since this is usually done on an application-wide basis to control debug output.

To restore the message handler, call qInstallMsgHandler(0).

Example:

    #include <qapplication.h>
    #include <stdio.h>
    #include <stdlib.h>

    void myMessageOutput( QtMsgType type, const char *msg )
    {
        switch ( type ) {
            case QtDebugMsg:
                fprintf( stderr, "Debug: %s\n", msg );
                break;
            case QtWarningMsg:
                fprintf( stderr, "Warning: %s\n", msg );
                break;
            case QtFatalMsg:
                fprintf( stderr, "Fatal: %s\n", msg );
                abort();                        // dump core on purpose
        }
    }

    int main( int argc, char **argv )
    {
        qInstallMsgHandler( myMessageOutput );
        QApplication a( argc, argv );
        ...
        return a.exec();
    }

See also: debug(), warning(), fatal() and Debugging

Q_EXPORT void qFatal (const char * msg, ...)

Prints a fatal error message and exits, or calls the message handler (if it has been installed).

This function takes a format string and a list of arguments, similar to the C printf() function.

Example:

    int divide( int a, int b )
    {
        if ( b == 0 )                           // program error
            qFatal( "divide: cannot divide by zero" );
        return a/b;
    }

Under X11, the text is printed to stderr. Under Windows, the text is sent to the debugger.

Warning: The internal buffer is limited to 512 bytes (including the 0-terminator).

See also: debug(), warning(), qInstallMsgHandler() and Debugging

Q_EXPORT const char * qVersion ()

Returns the Qt version number for the library, typically "1.30" or "1.31".

Q_EXPORT void qDebug (const char * msg, ...)

Prints a debug message, or calls the message handler (if it has been installed).

This function takes a format string and a list of arguments, similar to the C printf() function.

Example:

    qDebug( "my window handle = %x", myWidget->id() );

Under X11, the text is printed to stderr. Under Windows, the text is sent to the debugger.

Note: If DEBUG was not defined when the Qt library was built (i.e. NO_DEBUG was defined), this function does nothing.

Warning: The internal buffer is limited to 512 bytes (including the 0-terminator).

See also: warning(), fatal(), qInstallMsgHandler() and Debugging

Examples: qdir/qdir.cpp mainlyXt/editor.cpp

void qAddPostRoutine (Q_CleanUpFunction p)

Adds a global routine that will be called from the QApplication destructor. This function is normally used to add cleanup routines.

The function given by p should take no arguments and return nothing.

Example of use:

    static int *global_ptr = 0;

    void cleanup_ptr()
    {
        delete [] global_ptr;
    }

    void init_ptr()
    {
        global_ptr = new int[100];              // allocate data
        qAddPostRoutine( cleanup_ptr );         // delete later
    }

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Qt version 2.0.2