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Bug
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Resolution: Out of scope
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P2: Important
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None
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5.15.10, 6.6.1
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Windows
Hello,
I encountered strange behavior in QML when working with transitions. The main problem is that when transitioning between different states of objects, the properties of objects change several times instead of once. An example is given in the sample.
More detailed description:
Input: we have 2 simple QML objects inside a parent object, which has a state machine with two states. There is also a transitions element for state change animation:
Item {
id: mainItem
anchors.fill: parent
anchors.centerIn: parent
state: "HIDDEN"
Column {
anchors.topMargin: 100
anchors.fill: parent
spacing: 10
padding: 10
TestItem {
id: testItem
width: 100
height: 100
}
CustomItem {
id: customItem
width: 100
height: 100
Rectangle {
anchors.fill: parent
color: "transparent"
border.color: "black"
Text {
anchors.fill: parent
text: qsTr("customitem.cpp")
}
}
counter: 0
}
OtherItem {
id: otherItem
width: 100
height: 100
opacity: 1
}
}
states: [
State {
name: "HIDDEN"
PropertyChanges {
target: otherItem
color: getGreenColor()
opacity: 0
}
PropertyChanges {
target: testItem
customProperty: 0
}
PropertyChanges {
target: customItem
counter: 10
}
},
State {
name: "ACTIVE"
PropertyChanges {
target: testItem
customProperty: 1
}
PropertyChanges {
target: otherItem
color: getGreenColor()
opacity: 1
}
}
]
transitions: [
Transition {
from: "*"
to: "*"
PropertyAnimation {
target: otherItem
property: "opacity"
duration: 1000
}
}
]
}
When transitioning to the HIDDEN state, the color properties of the otherItem object are set through a call to the simple getGreenColor() function, and when transitioning to the ACTIVE state, the color is set directly. The problem is that when the testItem object enters the HIDDEN state, the customProperty property changes 3 times instead of one, here is the log of the testItem.onCustomPropertyChanged function call:
qml: TestItem customProperty: 0
qml: TestItem customProperty: 1
qml: TestItem customProperty: 0
But if you don’t use functions when changing properties, then the state changes once, as expected.
A quick debug showed that if a property of an object is changed with a call to the JS function, then QQuickTransitionManager sets properties for all objects in the QQuickStateAction::list, since in QQuickTransitionManagerPrivate::bindingsList it contains the binding for only this one object.
Could you please clarify if such behavior is expected?