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29 \page qdeclarativenetwork.html
31 \previouspage {Dynamic Object Management in QML}{Dynamic Object Management}
32 \nextpage {QML Internationalization}{Internationalization}
33 \contentspage QML Features
34 \title Network Transparency
36 QML supports network transparency by using URLs (rather than file names) for all
37 references from a QML document to other content:
41 source: "http://www.example.com/images/logo.png"
45 Since a \e relative URL is the same
46 as a relative file, development of QML on regular file systems remains simple:
50 source: "images/logo.png"
54 Network transparency is supported throughout QML, for example:
57 \o Fonts - the \c source property of FontLoader is a URL
58 \o WebViews - the \c url property of WebView (obviously!)
61 Even QML types themselves can be on the network - if the \l {QML Viewer} is used to load
62 \tt http://example.com/mystuff/Hello.qml and that content refers to a type "World", the engine
63 will load \tt http://example.com/mystuff/qmldir and resolve the type just as it would for a local file.
64 For example if the qmldir file contains the line "World World.qml", it will load
65 \tt http://example.com/mystuff/World.qml
66 Any other resources that \tt Hello.qml referred to, usually by a relative URL, would
67 similarly be loaded from the network.
70 \section1 Relative vs. Absolute URLs
72 Whenever an object has a property of type URL (QUrl), assigning a string to that
73 property will actually assign an absolute URL - by resolving the string against
74 the URL of the document where the string is used.
76 For example, consider this content in \tt{http://example.com/mystuff/test.qml}:
80 source: "images/logo.png"
84 The \l Image source property will be assigned \tt{http://example.com/mystuff/images/logo.png},
85 but while the QML is being developed, in say \tt C:\\User\\Fred\\Documents\\MyStuff\\test.qml, it will be assigned
86 \tt C:\\User\\Fred\\Documents\\MyStuff\\images\\logo.png.
88 If the string assigned to a URL is already an absolute URL, then "resolving" does
89 not change it and the URL is assigned directly.
92 \section1 Progressive Loading
94 Because of the declarative nature of QML and the asynchronous nature of network resources,
95 objects which reference network resource generally change state as the network resource loads.
96 For example, an Image with a network source will initially have
97 a \c width and \c height of 0, a \c status of \c Loading, and a \c progress of 0.0.
98 While the content loads, the \c progress will increase until
99 the content is fully loaded from the network,
100 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.
101 Applications can bind to these changing states to provide visual progress indicators where appropriate, or simply
102 bind to the \c width and \c height as if the content was a local file, adapting as those bound values change.
104 Note that when objects reference local files they immediately have the \c Ready status, but applications wishing
105 to remain network transparent should not rely on this. Future versions of QML may also use asynchronous local file I/O
106 to improve performance.
109 \section1 Accessing Network Services
111 QML types such as XmlListModel, and JavaScript classes like XMLHttpRequest are intended
112 entirely for accessing network services, which usually respond with references to
113 content by URLs that can then be used directly in QML. For example, using these facilities
114 to access an on-line photography service would provide the QML application with URLs to
115 photographs, which can be directly set on an \l Image \c source property.
117 See the \tt demos/declarative/flickr for a real demonstration of this.
120 \section1 Configuring the Network Access Manager
122 All network access from QML is managed by a QNetworkAccessManager set on the QDeclarativeEngine which executes the QML.
123 By default, this is an unmodified Qt QNetworkAccessManager. You may set a different manager by
124 providing a QDeclarativeNetworkAccessManagerFactory and setting it via
125 QDeclarativeEngine::setNetworkAccessManagerFactory().
126 For example, the \l {QML Viewer} sets a QDeclarativeNetworkAccessManagerFactory which
127 creates QNetworkAccessManager that trusts HTTP Expiry headers to avoid network cache checks,
128 allows HTTP Pipelining, adds a persistent HTTP CookieJar, a simple disk cache, and supports proxy settings.
131 \section1 QRC Resources
133 One of the URL schemes built into Qt is the "qrc" scheme. This allows content to be compiled into
134 the executable using \l{The Qt Resource System}. Using this, an executable can reference QML content
135 that is compiled into the executable:
138 QDeclarativeView *canvas = new QDeclarativeView;
139 canvas->setUrl(QUrl("qrc:/dial.qml"));
142 The content itself can then use relative URLs, and so be transparently unaware that the content is
143 compiled into the executable.
146 \section1 Limitations
148 The \c import statement is only network transparent if it has an "as" clause.
152 \o \c{import "dir"} only works on local file systems
153 \o \c{import libraryUri} only works on local file systems
154 \o \c{import "dir" as D} works network transparently
155 \o \c{import libraryUrl as U} works network transparently