Details
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Bug
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Resolution: Unresolved
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P3: Somewhat important
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None
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6.2.3, 6.3.2
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None
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Apple Silicon M1; macOS 12.1; Apple clang version 13.0.0 (clang-1300.0.29.30)
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macOS
Description
The following setup and combination of bindings causes odd behaviour. The Component.onCompleted statement should result in the list position at the beginning, but this does not happen when:
- ListView delegate width is an expression based on ListView width
- ListView sets left, top, width & height (to match parent) instead of using anchors.fill: parent
- ListView sits within a container
- The container width is an expression using parent.width (but not simply : parent.width)
- The container width is a numerical value
The following minimal code example implements this. (On the code in my actual project, as well as the position being offset, the delegate widths are also smaller than they should be but I could not reproduce this in the following code example.)
import QtQuick Window { id: root width: 800 height: 600 visible: true Item { id: container anchors.left: parent.left anchors.top: parent.top width: parent.width - 40 height: 200 ListView { id: listview anchors.left: parent.left anchors.top: parent.top width: parent.width height: parent.height orientation: Qt.Horizontal model: 20 delegate: Rectangle { width: listview.width / 8 height: listview.height border.color: "lightblue" border.width: 1 Text { anchors.fill: parent horizontalAlignment: Text.AlignHCenter verticalAlignment: Text.AlignVCenter text: model.index } Component.onCompleted: console.log("Delegate "+index+" created; width: "+width) onWidthChanged: console.log("Delegate "+index+"; width changed: "+width+" changed") Component.onDestruction: console.log("Delegate "+index+" destroyed") } Component.onCompleted: { positionViewAtBeginning(); console.log("ListView: "+width) } } } }
The console log output on starting the application is:
qml: Delegate 0; width changed: -5 changed qml: Delegate 0 created; width: -5 qml: Delegate 1; width changed: -5 changed qml: Delegate 1 created; width: -5 qml: Delegate 2; width changed: -5 changed qml: Delegate 2 created; width: -5 qml: Delegate 3; width changed: -5 changed qml: Delegate 3 created; width: -5 qml: Delegate 4; width changed: -5 changed qml: Delegate 4 created; width: -5 qml: Delegate 5; width changed: -5 changed qml: Delegate 5 created; width: -5 qml: Delegate 6; width changed: -5 changed qml: Delegate 6 created; width: -5 qml: Delegate 7; width changed: -5 changed qml: Delegate 7 created; width: -5 qml: Delegate 8; width changed: -5 changed qml: Delegate 8 created; width: -5 qml: Delegate 9; width changed: -5 changed qml: Delegate 9 created; width: -5 qml: Delegate 10; width changed: -5 changed qml: Delegate 10 created; width: -5 qml: Delegate 11; width changed: -5 changed qml: Delegate 11 created; width: -5 qml: Delegate 12; width changed: -5 changed qml: Delegate 12 created; width: -5 qml: Delegate 13; width changed: -5 changed qml: Delegate 13 created; width: -5 qml: Delegate 14; width changed: -5 changed qml: Delegate 14 created; width: -5 qml: Delegate 15; width changed: -5 changed qml: Delegate 15 created; width: -5 qml: Delegate 16; width changed: -5 changed qml: Delegate 16 created; width: -5 qml: Delegate 17; width changed: -5 changed qml: Delegate 17 created; width: -5 qml: Delegate 18; width changed: -5 changed qml: Delegate 18 created; width: -5 qml: Delegate 19; width changed: -5 changed qml: Delegate 19 created; width: -5 qml: Delegate 19; width changed: 95 changed qml: Delegate 18; width changed: 95 changed qml: Delegate 17; width changed: 95 changed qml: Delegate 16; width changed: 95 changed qml: Delegate 15; width changed: 95 changed qml: Delegate 14; width changed: 95 changed qml: Delegate 13; width changed: 95 changed qml: Delegate 12; width changed: 95 changed qml: Delegate 11; width changed: 95 changed qml: Delegate 10; width changed: 95 changed qml: Delegate 9; width changed: 95 changed qml: Delegate 8; width changed: 95 changed qml: Delegate 7; width changed: 95 changed qml: Delegate 6; width changed: 95 changed qml: Delegate 5; width changed: 95 changed qml: Delegate 4; width changed: 95 changed qml: Delegate 3; width changed: 95 changed qml: Delegate 2; width changed: 95 changed qml: Delegate 1; width changed: 95 changed qml: Delegate 0; width changed: 95 changed qml: ListView: 760 qml: Delegate 19 destroyed qml: Delegate 18 destroyed qml: Delegate 17 destroyed qml: Delegate 16 destroyed qml: Delegate 15 destroyed qml: Delegate 14 destroyed
My workaround has been to make delegate width & height based on container width & height instead of listview. It works but clearly this is a fragile fudge.
Possibly related to QTBUG-89568?
