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  1. Qt
  2. QTBUG-16971

Stray property change events when changing state and animating property

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      This was observed with code from qt-qml:qtquick11 and HEAD at eb55d07febf858474d8755e31cb554a4b8fabcdc
      Run the code below:

      import QtQuick 1.1

Item {
    id: root
    width: 640
    height: 480

    Loader {
        id: loader
        anchors.centerIn: parent
        onLoaded: {
            if(status == Loader.Ready) {
                print("Loader.Ready")
                item.opacity = 1;
                item.opacityChanged.connect(item, handleOpacityChanged);
            }
        }
    }

    function handleOpacityChanged() {
        print("opacity: " + this.opacity + "\t state: " + root.state)
        if(root.state == "hide" && this.opacity == 0) {
            print("UNLOAD")
//            root.state = ""
        }
    }

    MouseArea {
        anchors.fill: parent
        onClicked: parent.state = (parent.state == "" ? "show" : "hide")
    }

    states: [
        State {
            name: ""
            StateChangeScript { script: print("Applying '' state") }
        },
        State {
            name: "show"
            StateChangeScript { script: print("Applying 'show' state") }
            PropertyChanges { target: loader; sourceComponent: blueRect }
        },
        State {
            name: "hide"
            extend: "show"
            StateChangeScript { script: print("Applying 'hide' state") }
            PropertyChanges { target: loader.item; opacity: 0 }
        }
    ]

    Component {
        id: blueRect
        Rectangle {
            color: "blue"
            width: 100
            height: 100
            opacity: 0
            Behavior on opacity { NumberAnimation { duration: 100 }}
        }
    }
}

      Clicking on the screen once should give output similar to this:

      Loader.Ready
Applying 'show' state
Loader.Ready
opacity: 0.16	 state: show
opacity: 0.32	 state: show
opacity: 0.48	 state: show
opacity: 0.64	 state: show
opacity: 0.8	 state: show
opacity: 0.96	 state: show
opacity: 1	 state: show

      Except for the Loader.Ready status being notified twice despite fix for QTBUG-16319 being present the above looks correct.

      Click on the screen a second time. This will result in output similar to this:

      opacity: 0	 state: hide   <- (1)
UNLOAD                         <- (3)
opacity: 1	 state: hide   <- (2)
Applying 'show' state
Applying 'hide' state
opacity: 0.84	 state: hide
opacity: 0.67	 state: hide
opacity: 0.52	 state: hide
opacity: 0.36	 state: hide
opacity: 0.199	 state: hide
opacity: 0.040	 state: hide
opacity: 0	 state: hide
UNLOAD

      The issue is the stray opacity changes from fully opaque to fully transparent (1) and back to opaque (2) that happens just before the rectangle starts to fade out (manually marked in the log above). This results in "UNLOAD" being incorrectly printed too early (3), before the rectangle has actually faded out.

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            brasser Michael Brasser (closed Nokia identity) (Inactive)
            mathiasm Mathias Malmqvist
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              Created:
              Updated:
              Resolved:

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