source: trunk/doc/src/declarative/positioners.qdoc

/****************************************************************************
**
** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial Usage
** Licensees holding valid Qt Commercial licenses may use this file in
** accordance with the Qt Commercial License Agreement provided with the
** Software or, alternatively, in accordance with the terms contained in a
** written agreement between you and Nokia.
**
** GNU Free Documentation License
** 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.
**
** If you have questions regarding the use of this file, please contact
** Nokia at qt-info@nokia.com.
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
\page qml-positioners.html
\title Using QML Positioner and Repeater Items

\section1 Introduction

Positioner items are container items that manage the positions and sizes of
items in a declarative user interface. Positioners behave in a similar way to
the \l{Widgets and Layouts}{layout managers} used with standard Qt widgets,
except that they are also containers in their own right.

Positioners and repeaters make it easier to work with many items when they need
to be arranged in a regular layout.

\section1 Positioners

A set of standard positioners are provided in the basic set of Qt Quick
graphical elements:

\list
\o \l{#Column}{Column} arranges its children in a column
\o \l{#Row}{Row} arranges its children in a row
\o \l{#Grid}{Grid} arranges its children in a grid
\o \l{#Flow}{Flow} arranges its children like words on a page
\endlist

\section2 Column

\beginfloatright
\image qml-column.png
\endfloat

\l Column items are used to vertically arrange items. The following example
uses a Column item to arrange three \l Rectangle items in an area defined
by an outer \l Item. The \l{Column::spacing}{spacing} property is set to
include a small amount of space between the rectangles.

\clearfloat
\snippet doc/src/snippets/declarative/column/column.qml document

Note that, since Column inherits directly from Item, any background color
must be added to a parent Rectangle, if desired.

\section2 Row

\beginfloatright
\image qml-row.png
\endfloat

\l Row items are used to horizontally arrange items. The following example
uses a Row item to arrange three rounded \l Rectangle items in an area defined
by an outer colored Rectangle. The \l{Row::spacing}{spacing} property is set to
include a small amount of space between the rectangles.

We ensure that the parent Rectangle is large enough so that there is some space
left around the edges of the horizontally centered Row item.

\clearfloat
\snippet doc/src/snippets/declarative/row.qml document

\section2 Grid

\beginfloatright
\image qml-grid-spacing.png
\endfloat

\l Grid items are used to place items in a grid or table arrangement.
The following example uses a Grid item to place four \l Rectangle items
in a 2-by-2 grid. As with the other positioners, the spacing between items
can be specified using the \l{Grid::spacing}{spacing} property.

\clearfloat
\snippet doc/src/snippets/declarative/grid/grid-spacing.qml document

There is no difference between horizontal and vertical spacing inserted
between items, so any additional space must be added within the items
themselves.

Any empty cells in the grid must be created by defining placeholder items
at the appropriate places in the Grid definition.

\section2 Flow

\beginfloatright
\image qml-flow-text1.png
\image qml-flow-text2.png
\endfloat

\l Flow items are used to place items like words on a page, with rows or
columns of non-overlapping items.

Flow items arrange items in a similar way to \l Grid items, with items
arranged in lines along one axis (the minor axis), and lines of items
placed next to each other along another axis (the major axis). The
direction of flow, as well as the spacing between items, are controlled
by the \l{Flow::}{flow} and \l{Flow::}{spacing} properties.

The following example shows a Flow item containing a number of \l Text
child items. These are arranged in a similar way to those shown in the
screenshots.

\clearfloat
\snippet doc/src/snippets/declarative/flow.qml document

The main differences between the Grid and Flow positioners are that items
inside a Flow will wrap when they run out of space on the minor axis, and
items on one line may not be aligned with items on another line if the
items do not have uniform sizes. As with Grid items, there is no independent
control of spacing between items and between lines of items.

\section1 Repeaters

\beginfloatright
\image qml-repeater-grid-index.png
\endfloat

Repeaters create items from a template for use with positioners, using data
from a model. Combining repeaters and positioners is an easy way to lay out
lots of items. A \l Repeater item is placed inside a positioner, and generates
items that the enclosing positioner arranges.

Each Repeater creates a number of items by combining each element of data
from a model, specified using the \l{Repeater::model}{model} property, with
the template item, defined as a child item within the Repeater.
The total number of items is determined by the amount of data in the model.

The following example shows a repeater used with a \l{#Grid}{Grid} item to
arrange a set of Rectangle items. The Repeater item creates a series of 24
rectangles for the Grid item to position in a 5 by 5 arrangement.

\clearfloat
\snippet doc/src/snippets/declarative/repeaters/repeater-grid-index.qml document

The number of items created by a Repeater is held by its \l{Repeater::}{count}
property. It is not possible to set this property to determine the number of
items to be created. Instead, as in the above example, we use an integer as
the model. This is explained in the \l{QML Data Models#An Integer}{QML Data Models}
document.

It is also possible to use a delegate as the template for the items created
by a Repeater. This is specified using the \l{Repeater::}{delegate} property.

\section1 Using Transitions

Transitions can be used to animate items that are added to, moved within,
or removed from a positioner.

Transitions for adding items apply to items that are created as part of a
positioner, as well as those that are reparented to become children of a
positioner.
Transitions for removing items apply to items within a positioner that are
deleted, as well as those that are removed from a positioner and given new
parents in a document.

Additionally, changing the opacity of items to zero will cause them to
disappear using the remove transition, and making the opacity non-zero will
cause them to appear using the add transition.

\section1 Other Ways to Position Items

There are several other ways to position items in a user interface. In addition
to the basic technique of specifying their coordinates directly, they can be
positioned relative to other items with \l{anchor-layout}{anchors}, or used
with \l{QML Data Models} such as
\l{QML Data Models#VisualItemModel}{VisualItemModel}.
*/