Avoid double applyDelegateChange in QQIV::setDelegate

If a QQmlDelegateModel is used together with QQuickItemView, then we
will already call applyDelegateChange when the DelegateModel's
delegateChanged signal is emitted from QQmlDelegateModel::setDelegate.
Calling it manually in QQuickItemView's setDelegate is thus superfluous.

Fixes: QTBUG-102793
Fixes: QTBUG-107732
Change-Id: Ifffb23661813c4e71287538ec5342215dfbbdad6
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
(cherry picked from commit 2664b1988f031366c2616581e65b0e02e37e3ff1)
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

3 files changed, 58 insertions, 2 deletions

diff --git a/src/quick/items/qquickitemview.cpp b/src/quick/items/qquickitemview.cpp
index fda2e6ff79..7146b8d1b7 100644
--- a/src/quick/items/qquickitemview.cpp
+++ b/src/quick/items/qquickitemview.cpp
@@ -290,8 +290,6 @@ void QQuickItemView::setDelegate(QQmlComponent *delegate)
     if (QQmlDelegateModel *dataModel = qobject_cast<QQmlDelegateModel*>(d->model)) {
         int oldCount = dataModel->count();
         dataModel->setDelegate(delegate);
-        if (isComponentComplete())
-            d->applyDelegateChange();
         if (oldCount != dataModel->count())
             emit countChanged();
     }
diff --git a/tests/auto/quick/qquickvisualdatamodel/data/setDelegateNoDoubleChange.qml b/tests/auto/quick/qquickvisualdatamodel/data/setDelegateNoDoubleChange.qml
new file mode 100644
index 0000000000..05623fbc5b
--- /dev/null
+++ b/tests/auto/quick/qquickvisualdatamodel/data/setDelegateNoDoubleChange.qml
@@ -0,0 +1,43 @@
+import QtQuick 2.0
+
+Item {
+    width: 200
+    height: 200
+    id: root
+    property int creationCount: 0
+    property bool testStarted: false
+
+    ListModel {
+        id: mymodel
+        ListElement {message: "This is my alarm"}
+    }
+
+    Component {
+        id: aDelegate
+        Rectangle {
+            color: "blue"
+            width: 100
+            height: 100
+        }
+    }
+
+    Component {
+        id: bDelegate
+        Rectangle {
+            color: "red"
+            width: 100
+            height: 100
+            Text {text: model.message }
+            Component.onCompleted: root.creationCount++
+        }
+    }
+
+
+    ListView {
+        width: 200
+        height: 200
+        id: myListView
+        model: mymodel
+        delegate: testStarted ? bDelegate : aDelegate
+    }
+}
diff --git a/tests/auto/quick/qquickvisualdatamodel/tst_qquickvisualdatamodel.cpp b/tests/auto/quick/qquickvisualdatamodel/tst_qquickvisualdatamodel.cpp
index 27bd8aae49..83bdb1a5f8 100644
--- a/tests/auto/quick/qquickvisualdatamodel/tst_qquickvisualdatamodel.cpp
+++ b/tests/auto/quick/qquickvisualdatamodel/tst_qquickvisualdatamodel.cpp
@@ -434,6 +434,7 @@ private slots:
     void invalidContext();
     void externalManagedModel();
     void delegateModelChangeDelegate();
+    void noDoubleDelegateUpdate();
     void checkFilterGroupForDelegate();
     void readFromProxyObject();
 
@@ -4345,6 +4346,20 @@ void tst_qquickvisualdatamodel::delegateModelChangeDelegate()
     QCOMPARE(visualModel->count(), 3);
 }
 
+void tst_qquickvisualdatamodel::noDoubleDelegateUpdate()
+{
+    // changing a delegate only refreshes its instances once
+    QQmlEngine engine;
+    QQmlComponent component(&engine, testFileUrl("setDelegateNoDoubleChange.qml"));
+
+    QScopedPointer<QObject> root(component.create());
+    QVERIFY(root);
+
+    bool ok = root->setProperty("testStarted", true);
+    QVERIFY(ok);
+    QCOMPARE(root->property("creationCount").toInt(), 1);
+}
+
 void tst_qquickvisualdatamodel::checkFilterGroupForDelegate()
 {
     QQuickView view;