Qt Quick Examples - Threading¶
This is a collection of QML multithreading examples.
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:
<Code snippet "threading/threadedlistmodel/timedisplay.qml:0" not found>Inside the worker thread, the ListModel is synchronized once the data is finished loading:
<Code snippet "threading/threadedlistmodel/dataloader.mjs:0" not found>
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: (messageObject) => { 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; } } }
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