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
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
|
/****************************************************************************
**
** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the test suite of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** No Commercial Usage
** This file contains pre-release code and may not be distributed.
** You may use this file in accordance with the terms and conditions
** contained in the Technology Preview License Agreement accompanying
** this package.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 2.1 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL included in the
** packaging of this file. Please review the following information to
** ensure the GNU Lesser General Public License version 2.1 requirements
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain additional
** rights. These rights are described in the Nokia Qt LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** If you have questions regarding the use of this file, please contact
** Nokia at qt-info@nokia.com.
**
**
**
**
**
**
**
**
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\page qmlnetwork.html
\title Network Transparency
QML supports network transparency by using URLs (rather than file names) for all
references from a QML document to other content:
\qml
Image {
source: "http://www.example.com/images/logo.png"
}
\endqml
Since a \e relative URL is the same
as a relative file, development of QML on regular file systems remains simple:
\qml
Image {
source: "images/logo.png"
}
\endqml
Network transparency is supported throughout QML, for example:
\list
\o Scripts - the \c source property of \l Script is a URL
\o Fonts - the \c source property of FontLoader is a URL
\o WebViews - the \c url property of WebView (obviously!)
\endlist
Even QML types themselves can be on the network - if \l qmlviewer is used to load
\tt http://example.com/mystuff/Hello.qml and that content refers to a type "World", this
will load from \tt http://example.com/mystuff/World.qml just as it would for a local file.
Any other resources that \tt Hello.qml referred to, usually by a relative URL, would
similarly be loaded from the network.
\section1 Relative vs. Absolute URLs
Whenever an object has a property of type URL (QUrl), assigning a string to that
property will actually assign an absolute URL - by resolving the string against
the URL of the document where the string is used.
For example, consider this content in \tt{http://example.com/mystuff/test.qml}:
\qml
Image {
source: "images/logo.png"
}
\endqml
The \l Image source property will be assigned \tt{http://example.com/mystuff/images/logo.png},
but while the QML is being developed, in say \tt C:\\User\\Fred\\Documents\\MyStuff\\test.qml, it will be assigned
\tt C:\\User\\Fred\\Documents\\MyStuff\\images\\logo.png.
If the string assigned to a URL is already an absolute URL, then "resolving" does
not change it and the URL is assigned directly.
\section1 Progressive Loading
Because of the declarative nature of QML and the asynchronous nature of network resources,
objects which reference network resource generally change state as the network resource loads.
For example, an Image with a network source will initially have
a \c width and \c height of 0, a \c status of \c Loading, and a \c progress of 0.0.
While the content loads, the \c progress will increase until
the content is fully loaded from the network,
at which point the \c width and \c height become the content size, the \c status becomes \c Ready, and the \c progress reaches 1.0.
Applications can bind to these changing states to provide visual progress indicators where appropriate, or simply
bind to the \c width and \c height as if the content was a local file, adapting as those bound values change.
Note that when objects reference local files they immediately have the \c Ready status, but applications wishing
to remain network transparent should not rely on this. Future versions of QML may also use asynchronous local file I/O
to improve performance.
\section1 Accessing Network Services
QML types such as XmlListModel, and JavaScript classes like XMLHttpRequest are intended
entirely for accessing network services, which usually respond with references to
content by URLs that can then be used directly in QML. For example, using these facilities
to access an on-line photography service would provide the QML application with URLs to
photographs, which can be directly set on an \l Image \c source property.
See the \tt demos/declarative/flickr for a real demonstration of this.
\section1 Configuring the Network Access Manager
All network access from QML is managed by a QNetworkAccessManager set on the QmlEngine which executes the QML.
By default, this is an unmodified Qt QNetworkAccessManager. You may set a different manager using
QmlEngine::setNetworkAccessManager() as appropriate for the policies of your application.
For example, the \l qmlviewer tool sets a new QNetworkAccessManager which
trusts HTTP Expiry headers to avoid network cache checks, allows HTTP Pipelining, adds a persistent HTTP CookieJar,
a simple disk cache, and supports proxy settings.
\section1 QRC Resources
One of the URL schemes built into Qt is the "qrc" scheme. This allows content to be compiled into
the executable using \l{The Qt Resource System}. Using this, an executable can reference QML content
that is compiled into the executable:
\code
QmlView *canvas = new QmlView;
canvas->setUrl(QUrl("qrc:/dial.qml"));
\endcode
The content itself can then use relative URLs, and so be transparently unaware that the content is
compiled into the executable.
\section1 Limitations
The \c import statement is only network transparent if it has an "as" clause.
More specifically:
\list
\o \c{import "dir"} only works on local file systems
\o \c{import libraryUri} only works on local file systems
\o \c{import "dir" as D} works network transparently
\o \c{import libraryUrl as U} works network transparently
\endlist
*/
|
