c++qtqmlloaderqqmlcomponent

How to abort loading component in Loader?

I have a Loader object that loads some very heavy components. Some event arrives in the middle of the load that requires loading to stop and go back to empty the Loader. Is it possible?

Solution

  • Abort object creation

    As documented by Qt, three methods exists to unload/abort an object instantiation:

    1. Set Loader.active to false
    2. Set Loader.source to an empty string
    3. Set Loader.sourceComponent to undefined

    Asynchronous behaviour

    To be able to change these properties during loading, Loader.asynchronous should be true, otherwise the GUI thread is busy with loading the object. You also need to QQmlIncubationController for your QQmlEngine to control the idle time used for object incubation. Without such a controller Loader.asynchronous does not have any effect. Note that QQmlApplicationEngine automatically installs a default controller if the scene contains a QQuickWindow.

    Bug: memory leak

    Up to the last tested Qt version (Qt 5.8.0, 5.9.0 beta), a severe memory leaks exist when aborting an unfinished object incubation (at least in certain cases, including the example in the answer of derM) resulting in a fast memory usage increase for large components. A bug report is created including a proposed solution.

    According to the bug report, this should be fixed in Qt version 5.15 (not tested).