Qt Quick Examples - Threading▲
Threading is a collection of QML multithreading examples.
Running the Example▲
To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, visit Building and Running an Example.
Threaded ListModel▲
Threaded ListModel contains a ListView and a ListModel. The ListModel object is updated asynchronously in another thread, and the results propagate back to the main thread. A timer requests updates from the worker thread periodically:
Timer {
id: timer
interval: 2000; repeat: true
running: true
triggeredOnStart: true
onTriggered: {
var msg = {'action': 'appendCurrentTime', 'model': listModel};
worker.sendMessage(msg);
}
}Inside the worker thread, the ListModel is synchronized once the data is finished loading:
WorkerScript.onMessage = function(msg) {
if (msg.action == 'appendCurrentTime') {
var data = {'time': new Date().toTimeString()};
msg.model.append(data);
msg.model.sync(); // updates the changes to the list
}
}WorkerScript▲
WorkerScript contains an example of using a WorkerScript to offload expensive calculations into another thread. This keeps the UI from being blocked. This example calculates numbers in Pascal's Triangle, and not in a very optimal way, so it will often take several seconds to complete the calculation. By doing this in a WorkerScript in another thread, the UI is not blocked during this time.
When the UI needs another value, a request is sent to the WorkerScript:
Spinner {
id: rowSpinner
label: "Row"
onValueChanged: {
resultText.text = "Loading...";
myWorker.sendMessage( { row: rowSpinner.value, column: columnSpinner.value } );
}
}The workerscript then is free to take a really long time to calculate it:
WorkerScript.onMessage = function(message) {
//Calculate result (may take a while, using a naive algorithm)
var calculatedResult = triangle(message.row, message.column);
//Send result back to main thread
WorkerScript.sendMessage( { row: message.row,
column: message.column,
result: calculatedResult} );
}When it's done, the result returns to the main scene via the WorkerScript type:
WorkerScript {
id: myWorker
source: "workerscript.mjs"
onMessage: {
if (messageObject.row == rowSpinner.value && messageObject.column == columnSpinner.value){ //Not an old result
if (messageObject.result == -1)
resultText.text = "Column must be <= Row";
else
resultText.text = messageObject.result;
}
}
}