When a DelegateModel delegate changes, refill the view

It looked a bit odd that the DelegateModel delegate property was not a
notifying property.  Adding the delegateChanged signal makes it easier
to update the view when this happens.  The previous approach of removing
all delegates and adding all new ones resulted in the view losing its
currentIndex and often scrolling to a different place.  It's also nice
to reduce the number of d-> indirections by adding the
QQuickItemViewPrivate::applyDelegateChange() function, so that we just
need one indirection to call it, and then it updates all the internal
stuff in one place.

Done-with: Frederik Gladhorn
Done-with: Joni Poikelin
Fixes: QTBUG-63477
Change-Id: I2d17fd11ff4a2fcb20968a7182dd2c403abb715a
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 40 insertions, 0 deletions

diff --git a/tests/auto/quick/qquickvisualdatamodel/tst_qquickvisualdatamodel.cpp b/tests/auto/quick/qquickvisualdatamodel/tst_qquickvisualdatamodel.cpp
index 32008f675a..fe56cad018 100644
--- a/tests/auto/quick/qquickvisualdatamodel/tst_qquickvisualdatamodel.cpp
+++ b/tests/auto/quick/qquickvisualdatamodel/tst_qquickvisualdatamodel.cpp
@@ -432,6 +432,7 @@ private slots:
     void asynchronousCancel();
     void invalidContext();
     void externalManagedModel();
+    void delegateModelChangeDelegate();
 
 private:
     template <int N> void groups_verify(
@@ -4302,6 +4303,45 @@ void tst_qquickvisualdatamodel::externalManagedModel()
     QTRY_VERIFY(!object->property("running").toBool());
 }
 
+void tst_qquickvisualdatamodel::delegateModelChangeDelegate()
+{
+    // Verify that QTBUG-63477 is fixed.
+    // Changing the delegate would not update existing items.
+    QQmlEngine engine;
+    QScopedPointer<QQmlContext> context(new QQmlContext(engine.rootContext()));
+
+    QQmlComponent c(&engine);
+    c.setData("import QtQml.Models 2.2\nDelegateModel {}\n", QUrl());
+    QCOMPARE(c.status(), QQmlComponent::Ready);
+
+    QQmlDelegateModel *visualModel = qobject_cast<QQmlDelegateModel*>(c.create(context.data()));
+    QVERIFY(visualModel);
+    visualModel->setModel(QVariant(3));
+
+    QQmlComponent first(&engine);
+    first.setData("import QtQuick 2.0\nItem { objectName: \"old\" }\n", QUrl());
+    QCOMPARE(first.status(), QQmlComponent::Ready);
+
+    // Without delegate, claim to have an item count of 0
+    QCOMPARE(visualModel->count(), 0);
+
+    visualModel->setDelegate(&first);
+    // The first delegate has been set, verify we get it
+    QObject* old = visualModel->object(0, QQmlIncubator::Synchronous);
+    QVERIFY(old);
+    QCOMPARE(visualModel->object(0, QQmlIncubator::Synchronous)->objectName(), QStringLiteral("old"));
+    QCOMPARE(visualModel->count(), 3);
+
+    QQmlComponent second(&engine);
+    second.setData("import QtQuick 2.0\nItem { objectName: \"new\" }\n", QUrl());
+    QCOMPARE(second.status(), QQmlComponent::Ready);
+
+    visualModel->setDelegate(&second);
+    // After changing the delegate, expect the existing item to have the new delegate
+    QCOMPARE(visualModel->object(0, QQmlIncubator::Synchronous)->objectName(), QStringLiteral("new"));
+    QCOMPARE(visualModel->count(), 3);
+}
+
 QTEST_MAIN(tst_qquickvisualdatamodel)
 
 #include "tst_qquickvisualdatamodel.moc"