qt-everywhere-src-5.14.1/qtbase/examples/widgets/doc/src/basiclayouts.qdoc

/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** GNU Free Documentation License Usage
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
    \example layouts/basiclayouts
    \title Basic Layouts Example
    \brief Shows how to use the standard layout managers.

    \e{Basic Layouts} shows how to use the standard layout managers that are
    available in Qt: QBoxLayout, QGridLayout, and QFormLayout.

    \image basiclayouts-example.png Screenshot of the Basic Layouts example

    The QBoxLayout class lines up widgets horizontally or vertically.
    QHBoxLayout and QVBoxLayout are convenience subclasses of QBoxLayout.
    QGridLayout lays out widgets in cells by dividing the available space
    into rows and columns. QFormLayout, on the other hand, sets its
    children in a two-column form with labels in the left column and
    input fields in the right column.

    For more information, visit the \l{Layout Management} page.

    \include examples-run.qdocinc

    \section1 Dialog Class Definition

    \snippet layouts/basiclayouts/dialog.h 0

    The \c Dialog class inherits QDialog. It is a custom widget that
    displays its child widgets using the geometry managers:
    QHBoxLayout, QVBoxLayout, QGridLayout, and QFormLayout.

    There are four private functions to simplify the class
    constructor: the \c createMenu(), \c createHorizontalGroupBox(),
    \c createGridGroupBox(), and \c createFormGroupBox() functions create
    several widgets that the example uses to demonstrate how the layout
    affects their appearances.

    \section1 Dialog Class Implementation

    \snippet layouts/basiclayouts/dialog.cpp 0

    In the constructor, we first use the \c createMenu() function to
    create and populate a menu bar and the \c createHorizontalGroupBox()
    function to create a group box containing four buttons with a
    horizontal layout. Next, we use the \c createGridGroupBox() function
    to create a group box containing several line edits and a small text
    editor which are displayed in a grid layout. Finally, we use the
    \c createFormGroupBox() function to create a group box with
    three labels and three input fields: a line edit, a combo box, and
    a spin box.

    \snippet layouts/basiclayouts/dialog.cpp 1

    We also create a big text editor and a dialog button box. The
    QDialogButtonBox class is a widget that presents buttons in a
    layout that is appropriate to the current widget style. The
    preferred buttons can be specified as arguments to the
    constructor, using the QDialogButtonBox::StandardButtons enum.

    Note that we don't have to specify a parent for the widgets when
    we create them. The reason is that all the widgets we create here
    will be added to a layout, and when we add a widget to a layout,
    it is automatically reparented to the widget the layout is
    installed on.

    \snippet layouts/basiclayouts/dialog.cpp 2

    The main layout is a QVBoxLayout object. QVBoxLayout is a
    convenience class for a box layout with vertical orientation.

    In general, the QBoxLayout class takes the space it gets (from its
    parent layout or from the parent widget), divides it up into a
    series of boxes, and makes each managed widget fill one box.  If
    the QBoxLayout's orientation is Qt::Horizontal the boxes are
    placed in a row. If the orientation is Qt::Vertical, the boxes are
    placed in a column.  The corresponding convenience classes are
    QHBoxLayout and QVBoxLayout, respectively.

    \snippet layouts/basiclayouts/dialog.cpp 3

    When we call the QLayout::setMenuBar() function, the layout places
    the provided menu bar at the top of the parent widget, and outside
    the widget's \l {QWidget::contentsRect()}{content margins}. All
    child widgets are placed below the bottom edge of the menu bar.

    \snippet layouts/basiclayouts/dialog.cpp 4

    We use the QBoxLayout::addWidget() function to add the widgets to
    the end of the layout. Each widget will get at least its minimum size
    and at most its maximum size. It is possible to specify a stretch
    factor in the \l {QBoxLayout::addWidget()}{addWidget()} function,
    and any excess space is shared according to these stretch
    factors. If not specified, a widget's stretch factor is 0.

    \snippet layouts/basiclayouts/dialog.cpp 5

    We install the main layout on the \c Dialog widget using the
    QWidget::setLayout() function, and all of the layout's widgets are
    automatically reparented to be children of the \c Dialog widget.

    \snippet layouts/basiclayouts/dialog.cpp 6

    In the private \c createMenu() function we create a menu bar, and
    add a pull-down \uicontrol File menu containing an \uicontrol Exit option.

    \snippet layouts/basiclayouts/dialog.cpp 7

    When we create the horizontal group box, we use a QHBoxLayout as
    the internal layout. We create the buttons we want to put in the
    group box, add them to the layout and install the layout on the
    group box.

    \snippet layouts/basiclayouts/dialog.cpp 8

    In the \c createGridGroupBox() function we use a QGridLayout which
    lays out widgets in a grid. It takes the space made available to
    it (by its parent layout or by the parent widget), divides it up
    into rows and columns, and puts each widget it manages into the
    correct cell.

    \snippet layouts/basiclayouts/dialog.cpp 9

    For each row in the grid we create a label and an associated line
    edit, and add them to the layout. The QGridLayout::addWidget()
    function differ from the corresponding function in QBoxLayout: It
    needs the row and column specifying the grid cell to put the
    widget in.

    \snippet layouts/basiclayouts/dialog.cpp 10

    QGridLayout::addWidget() can in addition take arguments
    specifying the number of rows and columns the cell will be
    spanning. In this example, we create a small editor which spans
    three rows and one column.

    For both the QBoxLayout::addWidget() and QGridLayout::addWidget()
    functions it is also possible to add a last argument specifying
    the widget's alignment. By default it fills the whole cell. But we
    could, for example, align a widget with the right edge by
    specifying the alignment to be Qt::AlignRight.

    \snippet layouts/basiclayouts/dialog.cpp 11

    Each column in a grid layout has a stretch factor. The stretch
    factor is set using QGridLayout::setColumnStretch() and determines
    how much of the available space the column will get over and above
    its necessary minimum.

    In this example, we set the stretch factors for columns 1 and 2.
    The stretch factor is relative to the other columns in this grid;
    columns with a higher stretch factor take more of the available
    space. So column 2 in our grid layout will get more of the
    available space than column 1, and column 0 will not grow at all
    since its stretch factor is 0 (the default).

    Columns and rows behave identically; there is an equivalent
    stretch factor for rows, as well as a QGridLayout::setRowStretch()
    function.

    \snippet layouts/basiclayouts/dialog.cpp 12

    In the \c createFormGroupBox() function, we use a QFormLayout
    to neatly arrange objects into two columns - name and field.
    There are three QLabel objects for names with three
    corresponding input widgets as fields: a QLineEdit, a QComboBox
    and a QSpinBox. Unlike QBoxLayout::addWidget() and
    QGridLayout::addWidget(), we use QFormLayout::addRow() to add widgets
    to the layout.
*/