[Development] ListView.positionViewAtIndex() seems to be unreliable during object initialization

[Aleix Pol]

On Sat, May 31, 2014 at 11:19 PM, Baldo Davide <baldosoft at gmail.com> wrote:

> Hello,
>
> I'm having in issue with ListView.positionViewAtIndex(), i'm changing the
> index with the last selection of the user in Component.onCompleted(),
> but positionViewAtIndex() seems to behave randomly: sometime the listview
> is moved correctly, sometime is off by 1 or 2 items.
> I've been having this issue since 5.0 and i can still reproduce it on 5.3,
> i spent several hours trying to debug it but without luck, in the end i
> added a workaround:
>
> Timer {
>
>     interval: 100
>
>     repeat: false
>
>     running: true
>
>     onTriggered: {
>
>       main.alignIndex()
>
>     }
>
>  }.
> but it's really a bad solution, and it's even visible.
>
> Is it wrong to call positionViewAtIndex() inside Component.onCompleted()?
> If so, when should i call it?
>
> The component is a simple digit selector.
>
> --- CODE ---
>
> import QtQuick 2.0
>
>
> Rectangle {
>
>   id: main
>
>   width: 60
>
>   height: 180
>
>   color: "transparent"
>
>   border.color: "black"
>
>   border.width: 3
>
>   radius: 3
>
>   clip: true
>
>
>   property int initialDigit: 0;
>
>   property int digit: 0;
>
>   property string textColor: "violet";
>
>
>   function alignIndex()
>
>   {
>
>     var newIndex = main.digit + 50
>
>     listView.positionViewAtIndex(newIndex,ListView.Center);
>
>   }
>
>
>   /** workaround, force refresh after initialization **/
>
>   Timer {
>
>     interval: 100
>
>     repeat: false
>
>     running: true
>
>     onTriggered: {
>
>       main.alignIndex()
>
>     }
>
>   }
>
>
>   onDigitChanged: {
>
>     if( main.digit >= 10 ) {
>
>       main.digit = main.digit % 10
>
>     }
>
>     main.alignIndex()
>
>   }
>
>
>   Component.onCompleted: {
>
>     for( var i = 0; i < 10; i +=1 )
>
>     {
>
>       for( var n = 0; n < 10; n += 1 )
>
>       {
>
>         listModel.append({
>
>           digit: n
>
>         })
>
>       }
>
>     }
>
>
>     //console.log("initial digit: "+initialDigit)
>
>     digit = initialDigit
>
>     alignIndex();
>
>   }
>
>
>   Timer {
>
>     running: true
>
>     repeat: false
>
>     interval: 1
>
>     onTriggered: {
>
>       main.alignIndex()
>
>     }
>
>   }
>
>
>   ListView {
>
>     id: listView
>
>     anchors.fill: parent
>
>
>     snapMode: ListView.SnapPosition
>
>
>     Rectangle {
>
>       anchors.left: listView.left
>
>       anchors.right: listView.right
>
>       anchors.margins: 3
>
>       height: 60 * 0.8
>
>       y: main.height/2.0 - height/2.0 - 3
>
>       color: "#37ffffff"
>
>     }
>
>
>     onMovementEnded: {
>
>       main.digit = listView.indexAt(
>
>         listView.contentX,
>
>         listView.contentY + main.height/2.0
>
>       ) % 10
>
>     }
>
>
>     model: ListModel {
>
>       id: listModel
>
>     }
>
>
>     orientation: ListView.Vertical
>
>
>     delegate: Component
>
>     {
>
>       id: digitDelegate;
>
>       Item
>
>       {
>
>         height: 60
>
>         width: main.width
>
>         Text {
>
>           id: digitText
>
>           anchors.fill: parent
>
>           text: digit
>
>           font.pixelSize: parent.height * 0.8
>
>           verticalAlignment: Text.Center
>
>           horizontalAlignment: Text.Center
>
>
>           Component.onCompleted: {
>
>             digitText.color = main.textColor
>
>           }
>
>         }
>
>       }
>
>     }
>
>   }
>
> }
>
>
>
> --
> Regards,
> Davide Baldo
>
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>
>
You probably want to report this to the bug tracking system.
https://bugreports.qt-project.org

Aleix
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