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/****************************************************************************
**
** 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.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\page qtquicklayouts-overview.html
\title Qt Quick Layouts Overview
\brief A set of APIs for arranging QML items in a user interface.
Qt Quick Layouts are items that are used to arrange items in a user interface. Since Qt Quick
Layouts also resize their items, they are well suited for resizable user interfaces.
\section1 Getting Started
The QML types can be imported into your application using the following import statement in your \c {.qml} file.
\code
import QtQuick.Layouts 1.2
\endcode
\section1 Key Features
Some of the key features are:
\list
\li \l{Layout::alignment}{Alignment} of items can be specified with the
\l{Layout::alignment}{Layout.alignment} property
\li \l{Layout::fillWidth}{Resizable items} can be specified with the
\l{Layout::fillWidth}{Layout.fillWidth} and \l{Layout::fillHeight}{Layout.fillHeight}
properties.
\li \l{Size constraints} can be specified with
\l{Layout::minimumWidth}{Layout.minimumWidth},
\l{Layout::preferredWidth}{Layout.preferredWidth}, and
\l{Layout::maximumWidth}{Layout.maximumWidth} properties ("Width" can be replaced
with "Height" for specifying similar constraints to the height).
\li \l{RowLayout::spacing}{Spacings} can be specified with \l{RowLayout::spacing}{spacing},
\l{GridLayout::rowSpacing}{rowSpacing} or \l{GridLayout::columnSpacing}{columnSpacing}
\endlist
In addition to the above features, GridLayout adds these features:
\list
\li \l{Layout::row}{Grid coordinates} can be specified with the \l{Layout::row}{Layout.row} and
\l{Layout::column}{Layout.column} properties.
\li \l{GridLayout::flow}{Automatic grid coordinates} used together with the
\l{GridLayout::flow}{flow}, \l{GridLayout::rows}{rows}, and
\l{GridLayout::columns}{columns} properties.
\li \l{Layout::columnSpan}{Spans} across rows or columns can be specified with the
\l{Layout::rowSpan}{Layout.rowSpan} and \l{Layout::columnSpan}{Layout.columnSpan}
properties.
\endlist
\section1 Size Constraints
Since an item can be resized by its layout, the layout needs to know the
\l{Layout::minimumWidth}{minimum}, \l{Layout::preferredWidth}{preferred},
and \l{Layout::maximumWidth}{maximum} sizes of all items where \l{Layout::fillWidth}{Layout.fillWidth} or
\l{Layout::fillHeight}{Layout.fillHeight} is set to \c true.
For instance, the following will produce a layout with two rectangles lying side-by-side that
stretches horizontally. The azure rectangle can be resized from 50x150 to 300x150, and the plum
rectangle can be resized from 100x100 to ∞x100.
\snippet qml/windowconstraints.qml rowlayout
\image rowlayout-minimum.png "RowLayout at its minimum"
Combining each item's constraints will give these implicit constraints to the layout element:
\table
\header
\li
\li minimum
\li preferred
\li maximum
\row
\li implicit constraints (width)
\li 156
\li 306
\li ∞ (\c Number.POSITIVE_INFINITY)
\row
\li implicit constraints (heights)
\li 150
\li 150
\li 150
\endtable
Thus, the layout cannot be narrower than 156 or be taller or shorter than 150 without breaking
any of the constraints of its child items.
\section2 Specifying Preferred Size
For each item, the effective preferred size may come from one of several candidate properties.
For determining the effective preferred size, it will query these candidate properties in the
following order, and use the first candidate with a valid width or height.
\table
\header
\li Candidate properties
\li Description
\row
\li \l{Layout::preferredWidth}{Layout.preferredWidth} or
\l{Layout::preferredHeight}{Layout.preferredHeight}
\li These properties are supposed to be modified by the application if the default implicit
size does not give the optimal arrangement.
\row
\li \l{Item::implicitWidth}{implicitWidth} or \l{Item::implicitHeight}{implicitHeight}
\li These properties are supposed to be supplied by each item to give a meaningful ideal size,
for example the size needed to display all the contents of a \l Text type.
An implicit width or height of \c 0 is interpreted as invalid.
\row
\li \l{Item::width}{width} and \l{Item::height}{height}
\li If none of the above properties are valid, the layout will resort to the
\l{Item::width}{width} and \l{Item::height}{height} properties.
\endtable
An item can specify \l{Layout::preferredWidth}{Layout.preferredWidth} without having to specify
\l{Layout::preferredHeight}{Layout.preferredHeight}. In this case, the effective preferred
height will be determined from the \l{Item::implicitHeight}{implicitHeight} (or ultimately
\l{Item::height}{height}).
\note Resorting to \l{Item::width}{width} or \l{Item::height}{height} properties is only
provided as a final fallback. If you want to override the preferred size, it is recommended to
use \l{Layout::preferredWidth}{Layout.preferredWidth} or
\l{Layout::preferredHeight}{Layout.preferredHeight}. Relying on the \l{Item::width}{width} or
\l{Item::height}{height} properties for specifying the preferred size might give some
unexpected behavior. For instance, changing the \l{Item::width}{width} or
\l{Item::height}{height} properties won't trigger a layout rearrangement. Also, when the layout
is forced to do a full rebuild it might use the actual width and height, and not the width and
height specified in the QML file.
\section1 Connecting Windows and Layouts
You can just use normal anchoring concepts to ensure that the layout will follow the window
resizing.
\snippet qml/windowconstraints.qml anchoring
The size constraints of layouts can be used to ensure that the window cannot be resized beyond
the layout constraints. You can take the size constraints from the layout and set these
constraints on the minimumWidth, minimumHeight, maximumWidth, and maximumHeight of the Window
element. The following code ensures that the window cannot be resized beyond the constraints of
the layout:
\snippet qml/windowconstraints.qml bindconstraints
\note Since layout.Layout.maximumWidth is infinite in this case, we cannot bind that to the
maximumWidth property of Window, since that is an integer number. We therefore set a fixed
maximum width to 1000.
Finally, you usually want the initial size of the window to be the layout's implicit size:
\snippet qml/windowconstraints.qml binddefaultsize
*/
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