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<?xml version="1.0" encoding="UTF-8"?>
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  <title>Qt 4.8: QML Global Object</title>
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    <a href="index.html" class="qtref"><span>Qt Reference Documentation</span></a>
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<li>QML Global Object</li>
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<div class="toc">
<h3><a name="toc">Contents</a></h3>
<ul>
<li class="level1"><a href="#qt-object">Qt Object</a></li>
<li class="level1"><a href="#xmlhttprequest">XMLHttpRequest</a></li>
<li class="level1"><a href="#offline-storage-api">Offline Storage API</a></li>
<li class="level2"><a href="#database-api">Database API</a></li>
<li class="level3"><a href="#db-opendatabasesync-identifier-version-description-estimated-size-callback-db">db = openDatabaseSync(identifier, version, description, estimated_size, callback(db))</a></li>
<li class="level3"><a href="#db-changeversion-from-to-callback-tx">db.changeVersion(from, to, callback(tx))</a></li>
<li class="level3"><a href="#db-transaction-callback-tx">db.transaction(callback(tx))</a></li>
<li class="level3"><a href="#db-readtransaction-callback-tx">db.readTransaction(callback(tx))</a></li>
<li class="level3"><a href="#results-tx-executesql-statement-values">results = tx.executeSql(statement, values)</a></li>
<li class="level1"><a href="#logging">Logging</a></li>
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<h1 class="title">QML Global Object</h1>
<span class="subtitle"></span>
<!-- $$$qdeclarativeglobalobject.html-description -->
<div class="descr"> <a name="details"></a>
<p>Contains all the properties of the JavaScript global object, plus:</p>
<a name="qt-object"></a>
<h2>Qt Object</h2>
<p>The <a href="qml-qt.html#qmlglobalqtobject">Qt object</a> provides useful enums and functions from Qt, for use in all QML files.</p>
<a name="xmlhttprequest"></a>
<h2>XMLHttpRequest</h2>
<a name="xmlhttprequest"></a><p>QML script supports the <a href="#xmlhttprequest">XMLHttpRequest</a> object, which can be used to asynchronously obtain data from over a network.</p>
<p>The <a href="#xmlhttprequest">XMLHttpRequest</a> API implements the same <a href="http://www.w3.org/TR/XMLHttpRequest/">W3C standard</a> as many popular web browsers with following exceptions:</p>
<ul>
<li>QML's <a href="#xmlhttprequest">XMLHttpRequest</a> does not enforce the same origin policy.</li>
<li>QML's <a href="#xmlhttprequest">XMLHttpRequest</a> does not support <i>synchronous</i> requests.</li>
</ul>
<p>Additionally, the <tt>responseXML</tt> XML DOM tree currently supported by QML is a reduced subset of the <a href="http://www.w3.org/TR/DOM-Level-3-Core/">DOM Level 3 Core</a> API supported in a web browser. The following objects and properties are supported by the QML implementation:</p>
<table class="generic">
<thead><tr class="qt-style"><th ><b>Node</b></th><th ><b>Document</b></th><th ><b>Element</b></th><th ><b>Attr</b></th><th ><b>CharacterData</b></th><th ><b>Text</b></th></tr></thead>
<tr valign="top" class="odd"><td ><ul>
<li>nodeName</li>
<li>nodeValue</li>
<li>nodeType</li>
<li>parentNode</li>
<li>childNodes</li>
<li>firstChild</li>
<li>lastChild</li>
<li>previousSibling</li>
<li>nextSibling</li>
<li>attributes</li>
</ul>
</td><td ><ul>
<li>xmlVersion</li>
<li>xmlEncoding</li>
<li>xmlStandalone</li>
<li>documentElement</li>
</ul>
</td><td ><ul>
<li>tagName</li>
</ul>
</td><td ><ul>
<li>name</li>
<li>value</li>
<li>ownerElement</li>
</ul>
</td><td ><ul>
<li>data</li>
<li>length</li>
</ul>
</td><td ><ul>
<li>isElementContentWhitespace</li>
<li>wholeText</li>
</ul>
</td></tr>
</table>
<p>The <a href="declarative-xml-xmlhttprequest.html">XMLHttpRequest example</a> demonstrates how to use the <a href="#xmlhttprequest">XMLHttpRequest</a> object to make a request and read the response headers.</p>
<a name="offline-storage-api"></a>
<h2>Offline Storage API</h2>
<a name="database-api"></a>
<h3>Database API</h3>
<p>The <tt>openDatabaseSync()</tt> and related functions provide the ability to access local offline storage in an SQL database.</p>
<p>These databases are user-specific and QML-specific, but accessible to all QML applications. They are stored in the <tt>Databases</tt> subdirectory of <a href="qdeclarativeengine.html#offlineStoragePath-prop">QDeclarativeEngine::offlineStoragePath</a>(), currently as SQLite databases.</p>
<p>The API can be used from JavaScript functions in your QML:</p>
<pre class="qml"></pre>
<p>The API conforms to the Synchronous API of the HTML5 Web Database API, <a href="http://www.w3.org/TR/2009/WD-webdatabase-20091029/">W3C Working Draft 29 October 2009</a>.</p>
<p>The <a href="declarative-sqllocalstorage.html">SQL Local Storage example</a> demonstrates the basics of using the Offline Storage API.</p>
<a name="db-opendatabasesync-identifier-version-description-estimated-size-callback-db"></a>
<h4>db = openDatabaseSync(identifier, version, description, estimated_size, callback(db))</h4>
<p>Returns the database identified by <i>identifier</i>. If the database does not already exist, it is created, and the function <i>callback</i> is called with the database as a parameter. <i>description</i> and <i>estimated_size</i> are written to the INI file (described below), but are otherwise currently unused.</p>
<p>May throw exception with code property SQLException.DATABASE_ERR, or SQLException.VERSION_ERR.</p>
<p>When a database is first created, an INI file is also created specifying its characteristics:</p>
<table class="generic">
<thead><tr class="qt-style"><th ><b>Key</b></th><th ><b>Value</b></th></tr></thead>
<tr valign="top" class="odd"><td >Name</td><td >The name of the database passed to <tt>openDatabase()</tt></td></tr>
<tr valign="top" class="even"><td >Version</td><td >The version of the database passed to <tt>openDatabase()</tt></td></tr>
<tr valign="top" class="odd"><td >Description</td><td >The description of the database passed to <tt>openDatabase()</tt></td></tr>
<tr valign="top" class="even"><td >EstimatedSize</td><td >The estimated size (in bytes) of the database passed to <tt>openDatabase()</tt></td></tr>
<tr valign="top" class="odd"><td >Driver</td><td >Currently &quot;QSQLITE&quot;</td></tr>
</table>
<p>This data can be used by application tools.</p>
<a name="db-changeversion-from-to-callback-tx"></a>
<h4>db.changeVersion(from, to, callback(tx))</h4>
<p>This method allows you to perform a <i>Scheme Upgrade</i>.</p>
<p>If the current version of <i>db</i> is not <i>from</i>, then an exception is thrown.</p>
<p>Otherwise, a database transaction is created and passed to <i>callback</i>. In this function, you can call <i>executeSql</i> on <i>tx</i> to upgrade the database.</p>
<p>May throw exception with code property SQLException.DATABASE_ERR or SQLException.UNKNOWN_ERR.</p>
<a name="db-transaction-callback-tx"></a>
<h4>db.transaction(callback(tx))</h4>
<p>This method creates a read/write transaction and passed to <i>callback</i>. In this function, you can call <i>executeSql</i> on <i>tx</i> to read and modify the database.</p>
<p>If the callback throws exceptions, the transaction is rolled back.</p>
<a name="db-readtransaction-callback-tx"></a>
<h4>db.readTransaction(callback(tx))</h4>
<p>This method creates a read-only transaction and passed to <i>callback</i>. In this function, you can call <i>executeSql</i> on <i>tx</i> to read the database (with SELECT statements).</p>
<a name="results-tx-executesql-statement-values"></a>
<h4>results = tx.executeSql(statement, values)</h4>
<p>This method executes a SQL <i>statement</i>, binding the list of <i>values</i> to SQL positional parameters (&quot;?&quot;).</p>
<p>It returns a results object, with the following properties:</p>
<table class="generic">
<thead><tr class="qt-style"><th ><b>Type</b></th><th ><b>Property</b></th><th ><b>Value</b></th><th ><b>Applicability</b></th></tr></thead>
<tr valign="top" class="odd"><td >int</td><td >rows.length</td><td >The number of rows in the result</td><td >SELECT</td></tr>
<tr valign="top" class="even"><td >var</td><td >rows.item(i)</td><td >Function that returns row <i>i</i> of the result</td><td >SELECT</td></tr>
<tr valign="top" class="odd"><td >int</td><td >rowsAffected</td><td >The number of rows affected by a modification</td><td >UPDATE, DELETE</td></tr>
<tr valign="top" class="even"><td >string</td><td >insertId</td><td >The id of the row inserted</td><td >INSERT</td></tr>
</table>
<p>May throw exception with code property SQLException.DATABASE_ERR, SQLException.SYNTAX_ERR, or SQLException.UNKNOWN_ERR.</p>
<a name="logging"></a>
<h2>Logging</h2>
<p><tt>console.log()</tt> and <tt>console.debug()</tt> can be used to print information to the console. See <a href="qdeclarativedebugging.html">Debugging QML</a> for more information.</p>
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