Enables the use of threads in a Qt Quick application. 更多...
import 语句: | import QtQml.WorkerScript 2.15 |
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()
和
onMessage()
handler.
An example:
import QtQuick 2.0 Rectangle { width: 300; height: 300 Text { id: myText text: 'Click anywhere' } WorkerScript { id: myWorker source: "script.mjs" 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.mjs", that handles the operations to be performed in the new thread. Here is
script.mjs
:
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.mjs
. This in turn sends a reply message that is then received by the
onMessage()
handler of
myWorker
.
The example uses a script that is an ECMAScript module, because it has the ".mjs" extension. It can use import statements to access functionality from other modules and it is run in JavaScript strict mode.
If a worker script has the extension ".js" instead, then it is considered to contain plain JavaScript statements and it is run in non-strict mode.
注意: Each WorkerScript element will instantiate a separate JavaScript engine to ensure perfect isolation and thread-safety. If the impact of that results in a memory consumption that is too high for your environment, then consider sharing a WorkerScript element.
由于
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.mjs
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
QQmlContext
.
Additionally, there are restrictions on the types of values that can be passed to and from the worker script. See the sendMessage() 文档编制了解细节。
Worker scripts that are plain JavaScript sources can not use .import syntax. Scripts that are ECMAScript modules can freely use import and export statements.
另请参阅 Qt Quick Examples - Threading and Threaded ListModel Example .
ready : bool |
This holds whether the
WorkerScript
has been initialized and is ready for receiving messages via
WorkerScript.sendMessage()
.
source : url |
This holds the url of the JavaScript file that implements the
WorkerScript.onMessage()
handler for threaded operations.
If the file name component of the url ends with ".mjs", then the script is parsed as an ECMAScript module and run in strict mode. Otherwise it is considered to be plain script.
This signal is emitted when a message msg is received from a worker script in another thread through a call to sendMessage() .
注意:
相应处理程序是
onMessage
.
发送给定 message to a worker script handler in another thread. The other worker script handler can receive this message through the onMessage() handler.
The
message
object may only contain values of the following types:
All objects and arrays are copied to the
message
. With the exception of ListModel objects, any modifications by the other thread to an object passed in
message
will not be reflected in the original object.