Uploaded image for project: 'Qt'
  1. Qt
  2. QTBUG-82002

StatusChanged signal handler is called twice with identical status for asynchronous Loader

    XMLWordPrintable

Details

    • Windows
    • 1a7ca47a7a92945e16006ddd00adea186535cdd5 (qt/qtdeclarative/5.14)

    Description

      When using a Loader with the asynchronous property set to true and the component to load specified by assigning its URL to the source property, the onSignalChanged signal handler is called twice with identical status value Loader.Loading

      import QtQuick 2.12
import QtQuick.Window 2.12

Window {
    visible: true; width: 640; height: 480
    Loader {
        anchors.fill: parent
        asynchronous: true
        source: "qrc:/MyItem.qml"
        onStatusChanged: console.log("Loader status " + status)
    }
}

      Output:

      qml: Loader status 2
qml: Loader status 2
qml: Loader status 1

      If the code is changed such that the loader uses a local component of MyItem the behaviour is as expected:

      import QtQuick 2.12
import QtQuick.Window 2.12

Window {
    visible: true; width: 640; height: 480

    Loader {
        anchors.fill: parent
        asynchronous: true
        sourceComponent: mycomponent
        onStatusChanged: console.log("Loader status " + status)

        Component {
            id: mycomponent
            MyItem {}
        }
    }
}

      Output

      qml: Loader status 2
qml: Loader status 1

       
      In fact, just using MyItem inside the same component as the loader also fixes this bahviour:

      import QtQuick 2.12
import QtQuick.Window 2.12

Window {
    visible: true; width: 640; height: 480
    Loader {
        anchors.fill: parent
        asynchronous: true
        source: "qrc:/MyItem.qml"
        onStatusChanged: console.log("Loader status " + status)
    }

    MyItem {
        visible: false
    }
}

      Output

      qml: Loader status 2
qml: Loader status 1

      It is unclear to me if the signal is somehow emitted twice (but then since the status value remains the same, why is onStatusChanged even called the second time?) or if the loader in facts "restarts" loading the component.

      I experienced freezes of my application at startup when using the asynchronous loader in the "problematic" way, however I could not verify wether this is indeed a problem with the loader or a different issue in my application.
       

      Attachments

        1. LoaderTest.zip
          2 kB
          Michael Zimmer
        For Gerrit Dashboard: QTBUG-82002
        # Subject Branch Project Status CR V
        290298,4 QQuickLoader: store status 5.14 qt/qtdeclarative Status: MERGED +2 0

        Activity

          People

            fabiankosmale Fabian Kosmale
            miczim Michael Zimmer
            Votes:
            0 Vote for this issue
            Watchers:
            2 Start watching this issue

            Dates

              Created:
              Updated:
              Resolved:

              Gerrit Reviews

                There are no open Gerrit changes