QML animations visible property changes

问题

I want an animation to be painted when an element becomes visible (is should appear smoothly, not the whole at all)

I tried this

states: State
{
    name: "iconOff"
    when: iconOnSwitch.checked == false
    PropertyChanges { target: selectIconRow; visible: false }
}

transitions: Transition
{
    reversible: true
    from: ""
    to: "iconOff"
    PropertyAnimation
    {
        properties: "x,y,visible"
        easing.type: Easing.InOutQuad
        from: selectIconRow
        property: "visible"
    }
}

But the selectIconRow still appears immediately

How can I use such an animation?

回答1:

Because it's boolean, visible property cannot be animated. Perhaps opacity could do the trick.

回答2:

Here is how to do it with opacity:

Rectangle {
    id: myRect
    property bool stateVisible: true
    ...
    states: [
        State { when: stateVisible;
            PropertyChanges {   target: myRect; opacity: 1.0    }
        },
        State { when: !stateVisible;
            PropertyChanges {   target: myRect; opacity: 0.0    }
        }
    ]
    transitions: Transition {
        NumberAnimation { property: "opacity"; duration: 500}
    }
}

Keep in mind the advice of Vasco Rinaldo.

回答3:

I had to modify Uga Buga's answer slightly to make it work, here's what I got:

Rectangle {
    id: myRect
    property bool stateVisible: true
            ...
    states: [
        State { when: myRect.stateVisible; 
                PropertyChanges {   target: myRect; opacity: 1.0    }},
        State { when: !myRect.stateVisible;
                PropertyChanges {   target: myRect; opacity: 0.0    }}
    ]
    transitions: [ Transition { NumberAnimation { property: "opacity"; duration: 500}} ]
}

Please note that stateVisible is referenced through item id, it doesn't work without it on my system. Maybe some change in API caused this.

I also added square bracket in transitions field as an array is required there (although QML syntax seems to allow spelling without brackets)

回答4:

Just for future references, here's my solution which takes care also of Vasco's warning. Basically I'm animating the visible property of the component after the opacity has changed. It hurts seeing a NumberAnimation on a boolean, but it's working:

states: [
    State{
        name: "Visible"
        PropertyChanges{target: root; opacity: 1.0}
        PropertyChanges{target: root; visible: true}
    },
    State{
        name:"Invisible"
        PropertyChanges{target: root; opacity: 0.0}
        PropertyChanges{target: root; visible: false}
    }
]

transitions: [
        Transition {
            from: "Visible"
            to: "Invisible"

            SequentialAnimation{
               NumberAnimation {
                   target: root
                   property: "opacity"
                   duration: 500
                   easing.type: Easing.InOutQuad
               }
               NumberAnimation {
                   target: root
                   property: "visible"
                   duration: 0
               }
            }
        },
        Transition {
            from: "Invisible"
            to: "Visible"
            SequentialAnimation{
               NumberAnimation {
                   target: root
                   property: "visible"
                   duration: 0
               }
               NumberAnimation {
                   target: root
                   property: "opacity"
                   duration: 500
                   easing.type: Easing.InOutQuad
               }
            }
        }
    ]

This introduces also a transition when the component is vanishing.

回答5:

Item {

 scale: visible ? 1.0 : 0.1
 Behavior on scale { 
   NumberAnimation  { duration: 500 ; easing.type: Easing.InOutBounce  } 
  }

}

does the trick for me.

回答6:

visibility can be used in NumberAnimation, but to get the needed fading result, opacity animation could be used; like turning visibility ON from function like the following example:

Rectangle{
    id:fadingRect
    anchors.fill: parent
    visible: false
    opacity: 0.00
    color: "red"
    Component.onCompleted: {
        animRect.start()
    }
}
SequentialAnimation{
    id:animRect
    NumberAnimation { target: fadingRect; property: "visible"; from: 0; to:1; duration: 20}
    NumberAnimation { target: fadingRect; property: "opacity"; from: 0.00; to:1.00; duration: 4000 }

    onStopped: console.log(fadingRect.visible)
}

Or :

Rectangle{
    id:fadingRect
    anchors.fill: parent
    visible: false
    opacity: 1
    color: "red"
    Component.onCompleted: {
        animRect.start()
    }
        NumberAnimation { id:animRect; target: fadingRect; property: "opacity"; from: 0; to:1; duration: 2000;
        onStarted: { fadingRect.visible=true; console.log(fadingRect.visible)}
        }
}

来源：https://stackoverflow.com/questions/12333112/qml-animations-visible-property-changes