1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
|
/****************************************************************************
**
** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** 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.
**
** Other Usage
** Alternatively, this file may be used in accordance with the terms
** and conditions contained in a signed written agreement between you
** and Nokia.
**
**
**
**
**
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\page qtqml-modules-cppplugins.html
\title Creating C++ Plugins for QML
\brief Description of how to write C++ plugins for QML
\section1 Creating a Plugin
The \l{QQmlEngine}{QML engine} load C++ plugins for QML.
Such plugins are usually provided in a QML extension module, and can
provide types and functionality for use by clients in QML documents
which import the module.
QQmlExtensionPlugin is a plugin interface that makes it possible to
create QML extensions that can be loaded dynamically into QML applications.
These extensions allow custom QML types to be made available to the
QML engine.
To write a QML extension plugin:
\list 1
\li Subclass QQmlExtensionPlugin
\li Implement QQmlExtensionPlugin's
\l{QQmlExtensionPlugin::}{registerTypes()} method
\li Register types with qmlRegisterType()
\li Export the class using the Q_EXPORT_PLUGIN2() macro
\li Write a project file for the plugin
\li Create a \l{Syntax of a qmldir file}{qmldir file} to describe the plugin
\endlist
QML extension plugins are for either application-specific or library-like
plugins. Library plugins should limit themselves to registering types, as
any manipulation of the engine's root context may cause conflicts or other
issues in the library user's code.
\section1 Plugin Example
Suppose there is a new \c TimeModel C++ class that should be made available
as a new QML element. It provides the current time through \c hour and \c minute
properties.
\snippet examples/qml/cppextensions/plugins/plugin.cpp 0
\dots
A plugin class, \c QExampleQMLPlugin, is a subclass of
\l QQmlExtensionPlugin and it implements the
\l{QQmlExtensionPlugin::}{registerTypes()} method.
In the registerTypes() method, the plugin class can
register the \c TimeModel class to the declarative
runtime with the qmlRegisterType() function. The Q_EXPORT_PLUGIN2() macro has
two parameters, the generated plugin name and the class name.
\snippet examples/qml/cppextensions/plugins/plugin.cpp plugin
\codeline
\snippet examples/qml/cppextensions/plugins/plugin.cpp export
The \c TimeModel class receives a \c{1.0} version of this plugin library, as
a QML type called \c Time. The Q_ASSERT() macro can ensure the module is
imported correctly by any QML components that use this plugin. The
\l{Defining QML Object Types from C++} article has more information about registering C++
types into the runtime.
For this example, the TimeExample source directory is in
\c{com/nokia/TimeExample}. The plugin's module import statement will follow
this structure.
The project file, in a \c .pro file, defines the project as a plugin library
and specifies it should be built into the \c com/nokia/TimeExample
directory:
\code
TEMPLATE = lib
CONFIG += qt plugin
QT += declarative
DESTDIR = com/nokia/TimeExample
TARGET = qmlqtimeexampleplugin
...
\endcode
Finally, a \l{Syntax of a qmldir file}{qmldir file} is required in the \c
com/nokia/TimeExample directory to specify the plugin. This directory
includes a \c Clock.qml file that should be bundled with the plugin, so it
needs to be specified in the \c qmldir file:
\quotefile examples/qml/cppextensions/plugins/com/nokia/TimeExample/qmldir
Once the project is built and installed, the new \c Time component is
accessible by any QML component that imports the \c com.nokia.TimeExample
module
\snippet examples/qml/cppextensions/plugins/plugins.qml 0
The full source code is available in the \l {qml/cppextensions/plugins}{plugins example}.
\section1 Reference
\list
\li \l {Tutorial: Extending QML with C++} - contains a chapter
on creating QML plugins.
\li \l{Defining QML Object Types from C++} - information about registering C++ types into
the runtime.
\li \l{How to Create Qt Plugins} - information about Qt plugins
\endlist
*/
|
