WorkerScript Class Reference

The WorkerScript element enables the use of threads in QML. More...

Detailed Description

The WorkerScript element enables the use of threads in QML.

Use WorkerScript to run operations in a new thread. This is useful for running operations in the background so that the main GUI thread is not blocked.

Messages can be passed between the new thread and the parent thread using sendMessage() and the WorkerScript::onMessage{onMessage()} handler.

An example:

import QtQuick 1.0

Rectangle {
    width: 300; height: 300

    Text {
        id: myText
        text: 'Click anywhere'
    }

    WorkerScript {
        id: myWorker
        source: "script.js"

        onMessage: myText.text = messageObject.reply
    }

    MouseArea {
        anchors.fill: parent
        onClicked: myWorker.sendMessage({ 'x': mouse.x, 'y': mouse.y })
    }
}

The above worker script specifies a JavaScript file, "script.js", that handles the operations to be performed in the new thread. Here is script.js:

WorkerScript.onMessage = function(message) {
    // ... long-running operations and calculations are done here
    WorkerScript.sendMessage({ 'reply': 'Mouse is at ' + message.x + ',' + message.y })
}

When the user clicks anywhere within the rectangle, sendMessage() is called, triggering the WorkerScript.onMessage() handler in script.js. This in turn sends a reply message that is then received by the onMessage() handler of myWorker.

Restrictions

Since the WorkerScript.onMessage() function is run in a separate thread, the JavaScript file is evaluated in a context separate from the main QML engine. This means that unlike an ordinary JavaScript file that is imported into QML, the script.js in the above example cannot access the properties, methods or other attributes of the QML item, nor can it access any context properties set on the QML object through QDeclarativeContext.

Additionally, there are restrictions on the types of values that can be passed to and from the worker script. See the sendMessage() documentation for details.

See also

{declarative/threading/workerscript}{WorkerScript example}, {declarative/threading/threadedlistmodel}{Threaded ListModel example}

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The documentation for this class was generated from the following file:

• /src/declarative/qml/qdeclarativeworkerscript.cpp