Update scroll indicator position on content size change

If scroll indicator is at the beginning and data prepended to
contentItem, scroll indicator should change position to previous content
beginning.

This is especially important with so-called "infinite scrolling", when
scrolling goes upwards and new content added at the top of the view.

Task-number: QTBUG-50795
Change-Id: I250d6535b1146a54c6a70062b659cc49ed43709f
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

2 files changed, 53 insertions, 0 deletions

diff --git a/tests/auto/testplugin/testcppmodels.h b/tests/auto/testplugin/testcppmodels.h
index f5cc6298..6298bd13 100644
--- a/tests/auto/testplugin/testcppmodels.h
+++ b/tests/auto/testplugin/testcppmodels.h
@@ -96,6 +96,58 @@ private:
     QList<TestObject> m_testobject;
 };
 
+class TestFetchAppendModel : public QAbstractListModel
+{
+    Q_OBJECT
+public:
+    explicit TestFetchAppendModel(QObject *parent = 0)
+        : QAbstractListModel(parent) { }
+
+    virtual int rowCount(const QModelIndex &parent) const
+    {
+        if (parent.isValid()) {
+            return 0;
+        }
+
+        return m_data.size();
+    }
+    virtual QVariant data(const QModelIndex &index, int role) const
+    {
+        if (!index.isValid() || role != Qt::DisplayRole) {
+            return QVariant();
+        }
+
+        return QVariant::fromValue(index.row());
+    }
+
+    virtual bool canFetchMore(const QModelIndex &parent) const
+    {
+        Q_UNUSED(parent)
+
+        return true;
+    }
+    virtual void fetchMore(const QModelIndex & parent)
+    {
+        Q_UNUSED(parent)
+
+        addMoreData();
+    }
+
+private:
+    void addMoreData()
+    {
+        static const int insertCount = 20;
+
+        beginInsertRows(QModelIndex(), m_data.size(), m_data.size() + insertCount - 1);
+        for (int i = 0; i < insertCount; i++) {
+            m_data.append(int());
+        }
+        endInsertRows();
+    }
+
+    QList<int> m_data;
+};
+
 
 #endif // TESTCPPMODELS_H
 
diff --git a/tests/auto/testplugin/testplugin.cpp b/tests/auto/testplugin/testplugin.cpp
index 0f23f0b4..ee6a9711 100644
--- a/tests/auto/testplugin/testplugin.cpp
+++ b/tests/auto/testplugin/testplugin.cpp
@@ -48,6 +48,7 @@ void TestPlugin::registerTypes(const char *uri)
     qmlRegisterType<TestObject>(uri, 1, 0, "TestObject");
     qmlRegisterType<TestItemModel>(uri, 1, 0, "TestItemModel");
     qmlRegisterType<TestModel>(uri, 1, 0, "TreeModel");
+    qmlRegisterType<TestFetchAppendModel>(uri, 1, 0, "TestFetchAppendModel");
 }
 
 void TestPlugin::initializeEngine(QQmlEngine *engine, const char * /*uri*/)