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  1. Qt
  2. QTBUG-123882

QML list of length N emits (N+1) value change signals when shift() is called

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    Description

      Code

      import QtQuick
import QtQuick.Controls.Basic

Window {
    id: root
    width: 640
    height: 480
    visible: true

    property list<int> numbers: [1, 2, 3, 4, 5]
    onNumbersChanged: console.log("Updated list:", numbers)

    Button {
        text: "Shift"
        onClicked: {
            console.log("=== Starting shift ===")
            root.numbers.shift()
            console.log("=== Finished shift ===")
        }
    }
}

       

      Steps to reproduce
      Run the above code and click the button

       

      Expected outcomes

      qml: === Starting shift ===
qml: Updated list: [2,3,4,5]
qml: === Finished shift ===

       

      Actual outcomes

      qml: === Starting shift ===
qml: Updated list: [2,2,3,4,5]
qml: Updated list: [2,3,3,4,5]
qml: Updated list: [2,3,4,4,5]
qml: Updated list: [2,3,4,5,5]
qml: Updated list: [2,3,4,5,0]
qml: Updated list: [2,3,4,5]
qml: === Finished shift ===

       

      Notes
      There is a similar issue for pop():

      qml: === Starting pop ===
qml: Updated list: [1,2,3,4,0]
qml: Updated list: [1,2,3,4]
qml: === Finished pop ===

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        Issue Links

          resulted in

          Bug - A problem which impairs or prevents the functions of the product. QTBUG-123842 Excessive delegate creation+destruction when calling list<T>.shift() on ListView.model

          • P2: Important - Urgent, should be fixed, but will not stop the release.
          • Reported
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              qtqmlteam Qt Qml Team User
              skoh-qt Sze Howe Koh
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              Dates

                Created:
                Updated:

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