source: trunk/doc/src/windows-and-dialogs/mainwindow.qdoc@ 769

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/*!
    \group mainwindow-classes
    \title Main Window and Related Classes
*/

/*!
    \page application-windows.html
    \title Application Windows and Dialogs
    \ingroup frameworks-technologies

    \nextpage The Application Main Window

    A \l{Widgets Tutorial}{widget} that is not embedded in a parent widget is called a window.
    Usually, windows have a frame and a title bar, although it is also possible to create
    windows without such decoration using suitable window flags). In Qt, QMainWindow
    and the various subclasses of QDialog are the most common window types.

    In applications, windows provide the screen space upon which the user
    interface is built. Windows separate applications visually from each other
    and usually provide a window decoration that allows the user to resize and
    position the applications according to his preferences. Windows are typically
    integrated into the desktop environment and to some degree managed by the
    window management system that the desktop environment provides. For instance,
    selected windows of an application are represented in the task bar.

    \section1 Primary and Secondary Windows

    Any QWidget that has no parent will become a window, and will on most platforms
    be listed in the desktop's task bar. This is usually only wanted for one
    window in the application, the \e{primary window}.

    In addition, a QWidget that has a parent can become a window by setting the 
    \l{Qt::WindowType}{Qt::WA_Window} flag. Depending on the window management system
    such \e{secondary windows} are usually stacked on top of their respective parent
    window, and not have a task bar entry of their own.

    The QMainWindow and the QDialog classes set the Qt::WA_Window flag in their
    constructor, as they are designed to be used as windows and provide facilities
    that are not wanted for child widgets.

    \section1 Main Windows and Dialogs

    \l{The Application Main Window} provides the framework for building the
    application's main user interface, and are created by subclassing QMainWindow.
    QMainWindow has its own layout to which you can add a \l{QMenuBar}{menu bar},
    \l{QToolBar}{tool bars}, \l{QDockWidget}{dockable widgets} and a
    \l{QStatusBar}{status bar}. The center area can be occupied by any kind of
    QWidget.

    \l{Dialog Windows} are used as secondary windows that present the user with
    options and choices. Dialogs are created by subclassing QDialog and using
    \l{Widgets and Layouts}{widgets and layouts} to implement the user interface.
    In addition, Qt provides a number of ready-made standard dialogs that can be
    used for standard tasks like file or font selection.

    Both main windows and dialogs can be created with \QD, Qt's visual design tool.
    Using \QD is a lot faster than hand-coding, and makes it easy to test different
    design ideas. Creating designs visually and reading the code generated by
    \l{uic} is a great way to learn Qt!

    \keyword window geometry
    \section1 Window Geometry

    QWidget provides several functions that deal with a widget's
    geometry. Some of these functions operate on the pure client area
    (i.e. the window excluding the window frame), others include the
    window frame. The differentiation is done in a way that covers the
    most common usage transparently.

    \list
    \o \bold{Including the window frame:}
        \l{QWidget::x()}{x()},
        \l{QWidget::y()}{y()},
        \l{QWidget::frameGeometry()}{frameGeometry()},
        \l{QWidget::pos()}{pos()}, and
        \l{QWidget::move()}{move()}.
    \o \bold{Excluding the window frame:}
        \l{QWidget::geometry()}{geometry()},
        \l{QWidget::width()}{width()},
        \l{QWidget::height()}{height()},
        \l{QWidget::rect()}{rect()}, and
        \l{QWidget::size()}{size()}.
    \endlist

    Note that the distinction only matters for decorated top-level
    widgets. For all child widgets, the frame geometry is equal to the
    widget's client geometry.

    This diagram shows most of the functions in use:
    \img geometry.png Geometry diagram

    \section2 X11 Peculiarities

    On X11, a window does not have a frame until the window manager
    decorates it. This happens asynchronously at some point in time
    after calling QWidget::show() and the first paint event the
    window receives, or it does not happen at all. Bear in mind that
    X11 is policy-free (others call it flexible). Thus you cannot
    make any safe assumption about the decoration frame your window
    will get. Basic rule: There's always one user who uses a window
    manager that breaks your assumption, and who will complain to
    you.

    Furthermore, a toolkit cannot simply place windows on the screen. All
    Qt can do is to send certain hints to the window manager. The window
    manager, a separate process, may either obey, ignore or misunderstand
    them. Due to the partially unclear Inter-Client Communication
    Conventions Manual (ICCCM), window placement is handled quite
    differently in existing window managers.

    X11 provides no standard or easy way to get the frame geometry
    once the window is decorated. Qt solves this problem with nifty
    heuristics and clever code that works on a wide range of window
    managers that exist today. Don't be surprised if you find one
    where QWidget::frameGeometry() returns wrong results though.

    Nor does X11 provide a way to maximize a window.
    QWidget::showMaximized() has to emulate the feature. Its result
    depends on the result of QWidget::frameGeometry() and the
    capability of the window manager to do proper window placement,
    neither of which can be guaranteed.
*/

/*!
    \page mainwindow.html
    \title The Application Main Window
    \brief Everything you need for a typical modern main application window,
    including menus, toolbars, workspace, etc.

    \contentspage Application Windows and Dialogs
    \nextpage Dialog Windows

    \tableofcontents

    \section1 Overview of the Main Window Classes

    These classes provide everything you need for a typical modern main
    application window, like the main window itself, menu and tool bars,
    a status bar, etc.
    
    \annotatedlist mainwindow-classes

    \section1 The Main Window Classes

    Qt 4 provides the following classes for managing main windows and
    associated user interface components:

    \list
    \o QMainWindow remains the central class around which applications
       can be built. The interface to this class has been simplified, and
       much of the functionality previously included in this class is now
       present in the companion QDockWidget and QToolBar classes.

    \o QDockWidget provides a widget that can be used to create
       detachable tool palettes or helper windows. Dock widgets keep track
       of their own properties, and they can be moved, closed, and floated
       as external windows.

    \o QToolBar provides a generic toolbar widget that can hold a
       number of different action-related widgets, such as buttons,
       drop-down menus, comboboxes, and spin boxes. The emphasis on a
       unified action model in Qt 4 means that toolbars cooperate well
       with menus and keyboard shortcuts.
    \endlist

    \section1 Example Code

    Using QMainWindow is straightforward. Generally, we subclass
    QMainWindow and set up menus, toolbars, and dock widgets inside
    the QMainWindow constructor.

    To add a menu bar to the main window, we simply create the menus, and
    add them to the main window's menu bar. Note that the
    QMainWindow::menuBar() function will automatically create the menu bar
    the first time it is called. You can also call
    QMainWindow::setMenuBar() to use a custom menu bar in the main window.

    \snippet doc/src/snippets/code/doc_src_qt4-mainwindow.qdoc 0
    \dots
    \snippet examples/mainwindows/menus/mainwindow.cpp 5
    \dots

    Once actions have been created, we can add them to the main window
    components. To begin with, we add them to the pop-up menus:

    \snippet examples/mainwindows/menus/mainwindow.cpp 10
    \dots
    \snippet examples/mainwindows/menus/mainwindow.cpp 11
    \dots

    The QToolBar and QMenu classes use Qt's action system to provide a
    consistent API. In the above code, some existing actions were added to
    the file menu with the QMenu::addAction() function. QToolBar also
    provides this function, making it easy to reuse actions in different
    parts of the main window. This avoids unnecessary duplication of work.

    We create a toolbar as a child of the main window, and add the desired
    actions to it:

    \snippet examples/mainwindows/sdi/mainwindow.cpp 0
    \dots
    \snippet doc/src/snippets/code/doc_src_qt4-mainwindow.qdoc 1

    In this example, the toolbar is restricted to the top and bottom
    toolbar areas of the main window, and is initially placed in the
    top tool bar area. We can see that the actions specified by \c
    newAct and \c openAct will be displayed both on the toolbar and in
    the file menu.

    QDockWidget is used in a similar way to QToolBar. We create a
    dock widget as a child of the main window, and add widgets as children
    of the dock widget:

    \snippet doc/src/snippets/dockwidgets/mainwindow.cpp 0

    In this example, the dock widget can only be placed in the left and
    right dock areas, and it is initially placed in the left dock area. 

    The QMainWindow API allows the programmer to customize which dock
    widget areas occupy the four corners of the dock widget area. If
    required, the default can be changed with the
    QMainWindow::setCorner() function:

    \snippet doc/src/snippets/code/doc_src_qt4-mainwindow.qdoc 2

    The following diagram shows the configuration produced by the above code.
    Note that the left and right dock widgets will occupy the top and bottom
    corners of the main window in this layout.

    \image mainwindow-docks-example.png

    Once all of the main window components have been set up, the central widget
    is created and installed by using code similar to the following:

    \snippet doc/src/snippets/code/doc_src_qt4-mainwindow.qdoc 3

    The central widget can be any subclass of QWidget.
*/