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  1. Qt
  2. QTBUG-116723

TableView + TableModel discards every delegate with every update

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Details

    Description

      Delegates are destroyed/pooled too often.

      Note: Implementing similar code using ListView+ListModel does not exhibit this issue.

       

      Code

      import QtQuick 2.15
import QtQuick.Window 2.15
import Qt.labs.qmlmodels 1.0

Window {
    width: 640
    height: 480
    visible: true

    TableView {
        id: view
        anchors.fill: parent
        reuseItems: false

        model: TableModel {
            id: tableModel
            TableModelColumn { display: "A" }
        }
        delegate: Text {
            required property int modelData
            text: modelData

            TableView.onPooled: console.log("Pooled:", text)
            TableView.onReused: console.log("Reused:", text)
            Component.onCompleted: console.log("New:", text)
            Component.onDestruction: console.log("Destroyed:", text)
        }

        Timer {
            property int i: 0

            interval: 1000
            running: true
            repeat: true
            onTriggered: {
                console.log(`=== Row ${i} ===`)
                if (tableModel.rowCount >= 5)
                    tableModel.removeRow(0)
                tableModel.appendRow( {"A": i++} )
            }
        }
    }
}

       
      Expected Output
      If reuseItems == false

      qml: === Row 0 ===
qml: New: 0
qml: === Row 1 ===
qml: New: 1
qml: === Row 2 ===
qml: New: 2
qml: === Row 3 ===
qml: New: 3
qml: === Row 4 ===
qml: New: 4
qml: === Row 5 ===
qml: Destroyed: 0
qml: New: 5
...

       

      If reuseItems == true

      qml: === Row 0 ===
qml: New: 0
qml: === Row 1 ===
qml: New: 1
qml: === Row 2 ===
qml: New: 2
qml: === Row 3 ===
qml: New: 3
qml: === Row 4 ===
qml: New: 4
qml: === Row 5 ===
qml: Pooled: 0
qml: Reused: 5
...

       

      Actual Output
      If reuseItems == false

      qml: === Row 0 ===
qml: New: 0
qml: === Row 1 ===
qml: Destroyed: 0
qml: New: 0
qml: New: 1
qml: === Row 2 ===
qml: Destroyed: 1
qml: Destroyed: 0
qml: New: 0
qml: New: 1
qml: New: 2
qml: === Row 3 ===
qml: Destroyed: 1
qml: Destroyed: 0
qml: Destroyed: 2
qml: New: 0
qml: New: 1
qml: New: 2
qml: New: 3
qml: === Row 4 ===
qml: Destroyed: 1
qml: Destroyed: 3
qml: Destroyed: 0
qml: Destroyed: 2
qml: New: 0
qml: New: 1
qml: New: 2
qml: New: 3
qml: New: 4
qml: === Row 5 ===
qml: Destroyed: 4
qml: Destroyed: 1
qml: Destroyed: 3
qml: Destroyed: 0
qml: Destroyed: 2
qml: New: 1
qml: New: 2
qml: New: 3
qml: New: 4
qml: New: 5
...

       

      If reuseItems == true

      qml: === Row 0 ===
qml: New: 0
qml: === Row 1 ===
qml: Pooled: 0
qml: Reused: 0
qml: New: 1
qml: === Row 2 ===
qml: Pooled: 0
qml: Pooled: 1
qml: Reused: 0
qml: Reused: 1
qml: New: 2
qml: === Row 3 ===
qml: Pooled: 2
qml: Pooled: 0
qml: Pooled: 1
qml: Reused: 0
qml: Reused: 1
qml: Reused: 2
qml: New: 3
qml: === Row 4 ===
qml: Pooled: 2
qml: Pooled: 0
qml: Pooled: 1
qml: Pooled: 3
qml: Reused: 0
qml: Reused: 1
qml: Reused: 2
qml: Reused: 3
qml: New: 4
qml: === Row 5 ===
qml: Pooled: 2
qml: Pooled: 4
qml: Pooled: 0
qml: Pooled: 1
qml: Pooled: 3
qml: Reused: 1
qml: Reused: 2
qml: Reused: 3
qml: Reused: 4
qml: Reused: 5
...

      Attachments

        Issue Links

          duplicates

          Bug - A problem which impairs or prevents the functions of the product. QTBUG-116650 TableView rebuilds the entire table when a single row is added/removed

          • P2: Important - Urgent, should be fixed, but will not stop the release.
          • Reported
          is duplicated by

          Bug - A problem which impairs or prevents the functions of the product. QTBUG-119144 QML Views: Too many delegates instantiated unnecessarily with (begin|end)InsertRows()

          • P2: Important - Urgent, should be fixed, but will not stop the release.
          • Closed
          is required for

          User Story - Created by Jira Software - do not edit or delete. Issue type for a user story. QTBUG-70326 TableView

          • P2: Important - Urgent, should be fixed, but will not stop the release.
          • In Progress
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              richard Richard Moe Gustavsen
              skoh-qt Sze Howe Koh
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              Dates

                Created:
                Updated:
                Resolved:

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