source: trunk/doc/src/declarative/globalobject.qdoc@ 846

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/*!
\page qdeclarativeglobalobject.html
\title QML Global Object

Contains all the properties of the JavaScript global object, plus:

\tableofcontents

\section1 Qt Object

The \l{QmlGlobalQtObject}{Qt object} provides useful enums and functions from Qt, for use in all QML
files. 

\section1 XMLHttpRequest

\target XMLHttpRequest

QML script supports the XMLHttpRequest object, which can be used to asynchronously obtain 
data from over a network.  

The XMLHttpRequest API implements the same \l {http://www.w3.org/TR/XMLHttpRequest/}{W3C standard}
as many popular web browsers with following exceptions:
\list
\i QML's XMLHttpRequest does not enforce the same origin policty.
\i QML's XMLHttpRequest does not support \e synchronous requests.
\endlist

Additionally, the \c responseXML XML DOM tree currently supported by QML is a reduced subset
of the \l {http://www.w3.org/TR/DOM-Level-3-Core/}{DOM Level 3 Core} API supported in a web
browser.  The following objects and properties are supported by the QML implementation:

\table
\header
\o \bold {Node}
\o \bold {Document}
\o \bold {Element}
\o \bold {Attr}
\o \bold {CharacterData}
\o \bold {Text}

\row
\o 
\list
\o nodeName
\o nodeValue
\o nodeType
\o parentNode
\o childNodes
\o firstChild
\o lastChild
\o previousSibling
\o nextSibling
\o attribtes
\endlist

\o 
\list
\o xmlVersion
\o xmlEncoding
\o xmlStandalone
\o documentElement
\endlist

\o
\list 
\o tagName
\endlist

\o
\list
\o name
\o value
\o ownerElement
\endlist

\o
\list 
\o data
\o length
\endlist

\o
\list
\o isElementContentWhitespace
\o wholeText
\endlist

\endtable

The \l{declarative/xml/xmlhttprequest}{XMLHttpRequest example} demonstrates how to
use the XMLHttpRequest object to make a request and read the response headers.

\section1 Offline Storage API

\section2 Database API

The \c openDatabaseSync() and related functions
provide the ability to access local offline storage in an SQL database.

These databases are user-specific and QML-specific, but accessible to all QML applications.
They are stored in the \c Databases subdirectory
of QDeclarativeEngine::offlineStoragePath(), currently as SQLite databases.

The API can be used from JavaScript functions in your QML:

\snippet declarative/sqllocalstorage/hello.qml 0

The API conforms to the Synchronous API of the HTML5 Web Database API,
\link http://www.w3.org/TR/2009/WD-webdatabase-20091029/ W3C Working Draft 29 October 2009\endlink.

The \l{declarative/sqllocalstorage}{SQL Local Storage example} demonstrates the basics of
using the Offline Storage API.

\section3 db = openDatabaseSync(identifier, version, description, estimated_size, callback(db))

Returns the database identified by \e identifier. If the database does not already exist, it
is created with the properties \e description and \e estimated_size and the function \e callback
is called with the database as a parameter.

May throw exception with code property SQLException.DATABASE_ERR, or SQLException.VERSION_ERR.

When a database is first created, an INI file is also created specifying its characteristics:

\table
\header \o \bold {Key} \o \bold {Value}
\row \o Name \o The name of the database passed to \c openDatabase()
\row \o Version \o The version of the database passed to \c openDatabase()
\row \o Description \o The description of the database passed to \c openDatabase()
\row \o EstimatedSize \o The estimated size of the database passed to \c openDatabase()
\row \o Driver \o Currently "QSQLITE"
\endtable

This data can be used by application tools.

\section3 db.changeVersion(from, to, callback(tx))

This method allows you to perform a \e{Scheme Upgrade}.

If the current version of \e db is not \e from, then an exception is thrown.

Otherwise, a database transaction is created and passed to \e callback. In this function,
you can call \e executeSql on \e tx to upgrade the database.

May throw exception with code property SQLException.DATABASE_ERR or SQLException.UNKNOWN_ERR.

\section3 db.transaction(callback(tx))

This method creates a read/write transaction and passed to \e callback. In this function,
you can call \e executeSql on \e tx to read and modify the database.

If the callback throws exceptions, the transaction is rolled back.

\section3 db.readTransaction(callback(tx))

This method creates a read-only transaction and passed to \e callback. In this function,
you can call \e executeSql on \e tx to read the database (with SELECT statements).

\section3 results = tx.executeSql(statement, values)

This method executes a SQL \e statement, binding the list of \e values to SQL positional parameters ("?").

It returns a results object, with the following properties:

\table
\header \o \bold {Type} \o \bold {Property} \o \bold {Value} \o \bold {Applicability}
\row \o int \o rows.length \o The number of rows in the result \o SELECT
\row \o var \o rows.item(i) \o Function that returns row \e i of the result \o SELECT
\row \o int \o rowsAffected \o The number of rows affected by a modification \o UPDATE, DELETE
\row \o string \o insertId \o The id of the row inserted \o INSERT
\endtable

May throw exception with code property SQLException.DATABASE_ERR, SQLException.SYNTAX_ERR, or SQLException.UNKNOWN_ERR.

\section1 Logging

\c console.log() and \c console.debug() can be used to print information
to the console. See \l{Debugging QML} for more information.

*/