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authorWarwick Allison <warwick.allison@nokia.com>2009-10-14 03:16:19 (GMT)
committerWarwick Allison <warwick.allison@nokia.com>2009-10-14 03:16:19 (GMT)
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\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. Since a \i relative URL is the same
+as a relative file, development of QML on regular file systems remains simple.
+
+\section1 Accessing Network Reesources from QML
+
+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 \c{http://example.com/mystuff/test.qml}:
+
+\code
+Image {
+ source: "images/logo.png"
+}
+\endcode
+
+The \l Image source property will be assigned \c{http://example.com/mystuff/images/logo.png},
+but while the QML is being developed, in say \c C:\User\Fred\Documents\MyStuff\test.qml, it will be assigned
+\c C:\User\Fred\Documents\MyStuff\images\logo.png.
+
+Network transparency is supported throughout QML:
+
+\list
+\o Types - if the \c test.qml file above used "Hello { }", that would refer to \c http://example.com/mystuff/Hello.qml
+\o Scripts - the \c source property of \l Script is a URL
+\o Images - the \c source property of \l Image and similar types is a URL
+\o Fonts - the \c source property of FontLoader is a URL
+\o WebViews - the \c url property of WebView may be assigned a relative URL string
+\endlist
+
+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 Limitations
+
+The \c import statement only works network transparently if it has an "as" clause.
+
\list
-\o Documents and script blocks can be fetched transparently over the network (blocking)
-\o Images, fonts can be fetched transparently over the network (non-blocking)
-\o Configuring the network access manager
-\o Relative URL resolution from ECMAScript/QML
+\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
+\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 eample, 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.
+
*/