3 files changed, 86 insertions, 13 deletions

diff --git a/src/quick/items/qquicktableview.cpp b/src/quick/items/qquicktableview.cpp
index e1ec5aff75..a1a5520239 100644
--- a/src/quick/items/qquicktableview.cpp
+++ b/src/quick/items/qquicktableview.cpp
@@ -771,13 +771,11 @@ void QQuickTableViewPrivate::layoutHorizontalEdge(Qt::Edge tableEdge)
 
 void QQuickTableViewPrivate::layoutTopLeftItem()
 {
-    // ###todo: support starting with other top-left items than 0,0
     const QPoint cell = loadRequest.firstCell();
-    Q_TABLEVIEW_ASSERT(cell == QPoint(0, 0), loadRequest.toString());
     auto topLeftItem = loadedTableItem(cell);
     auto item = topLeftItem->item;
 
-    item->setPosition(QPoint(tableMargins.left(), tableMargins.top()));
+    item->setPosition(loadRequest.startPosition());
     item->setSize(QSizeF(resolveColumnWidth(cell.x()), resolveRowHeight(cell.y())));
     topLeftItem->setVisible(true);
     qCDebug(lcTableViewDelegateLifecycle) << "geometry:" << topLeftItem->geometry();
@@ -938,18 +936,35 @@ void QQuickTableViewPrivate::beginRebuildTable()
     if (loadRequest.isActive())
         cancelLoadRequest();
 
-    releaseLoadedItems(QQmlTableInstanceModel::NotReusable);
+    QPoint topLeft;
+    QPointF topLeftPos;
+    calculateTableSize();
+
+    if (rebuildOptions & RebuildOption::All) {
+        releaseLoadedItems(QQmlTableInstanceModel::NotReusable);
+        topLeft = QPoint(0, 0);
+        topLeftPos = QPointF(tableMargins.left(), tableMargins.top());
+        q->setContentX(0);
+        q->setContentY(0);
+    } else if (rebuildOptions & RebuildOption::ViewportOnly) {
+        // Rebuild the table without flicking the content view back to origin, and
+        // start building from the same top left item that is currently showing
+        // (unless it has been removed from the model).
+        releaseLoadedItems(reusableFlag);
+        topLeft = loadedTable.topLeft();
+        topLeftPos = loadedTableOuterRect.topLeft();
+        topLeft.setX(qMin(topLeft.x(), tableSize.width() - 1));
+        topLeft.setY(qMin(topLeft.y(), tableSize.height() - 1));
+    } else {
+        Q_TABLEVIEW_UNREACHABLE(rebuildOptions);
+    }
 
     loadedTable = QRect();
     loadedTableOuterRect = QRect();
     loadedTableInnerRect = QRect();
     contentSizeBenchMarkPoint = QPoint(-1, -1);
 
-    q->setContentX(0);
-    q->setContentY(0);
-
-    calculateTableSize();
-    loadInitialTopLeftItem();
+    loadInitialTopLeftItem(topLeft, topLeftPos);
     loadAndUnloadVisibleEdges();
 }
 
@@ -965,7 +980,7 @@ void QQuickTableViewPrivate::layoutAfterLoadingInitialTable()
     }
 }
 
-void QQuickTableViewPrivate::loadInitialTopLeftItem()
+void QQuickTableViewPrivate::loadInitialTopLeftItem(const QPoint &cell, const QPointF &pos)
 {
     Q_TABLEVIEW_ASSERT(loadedItems.isEmpty(), "");
 
@@ -980,7 +995,7 @@ void QQuickTableViewPrivate::loadInitialTopLeftItem()
 
     // Load top-left item. After loaded, loadItemsInsideRect() will take
     // care of filling out the rest of the table.
-    loadRequest.begin(QPoint(0, 0), QQmlIncubator::AsynchronousIfNested);
+    loadRequest.begin(cell, pos, QQmlIncubator::AsynchronousIfNested);
     processLoadRequest();
 }
 
diff --git a/src/quick/items/qquicktableview_p_p.h b/src/quick/items/qquicktableview_p_p.h
index 81127adae4..1e8c10c285 100644
--- a/src/quick/items/qquicktableview_p_p.h
+++ b/src/quick/items/qquicktableview_p_p.h
@@ -86,7 +86,7 @@ public:
         // done by QQuickTableView.
 
     public:
-        void begin(const QPoint &cell, QQmlIncubator::IncubationMode incubationMode)
+        void begin(const QPoint &cell, const QPointF &pos, QQmlIncubator::IncubationMode incubationMode)
         {
             Q_ASSERT(!active);
             active = true;
@@ -95,6 +95,7 @@ public:
             mode = incubationMode;
             cellCount = 1;
             currentIndex = 0;
+            startPos = pos;
             qCDebug(lcTableViewDelegateLifecycle()) << "begin top-left:" << toString();
         }
 
@@ -125,6 +126,8 @@ public:
         inline Qt::Edge edge() { return tableEdge; }
         inline QQmlIncubator::IncubationMode incubationMode() { return mode; }
 
+        inline QPointF startPosition() { return startPos; }
+
         QString toString()
         {
             QString str;
@@ -154,6 +157,7 @@ public:
         int cellCount = 0;
         bool active = false;
         QQmlIncubator::IncubationMode mode = QQmlIncubator::AsynchronousIfNested;
+        QPointF startPos;
 
         QPoint cellAt(int index)
         {
@@ -304,7 +308,7 @@ public:
     void unloadItem(const QPoint &cell);
     void unloadItems(const QLine &items);
 
-    void loadInitialTopLeftItem();
+    void loadInitialTopLeftItem(const QPoint &cell, const QPointF &pos);
     void loadEdge(Qt::Edge edge, QQmlIncubator::IncubationMode incubationMode);
     void unloadEdge(Qt::Edge edge);
     void loadAndUnloadVisibleEdges();
diff --git a/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp b/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp
index 99534ddb50..e5b06051a5 100644
--- a/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp
+++ b/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp
@@ -130,6 +130,7 @@ private slots:
     void checkContextPropertiesQQmlListProperyModel();
     void checkRowAndColumnChangedButNotIndex();
     void checkChangingModelFromDelegate();
+    void checkRebuildViewportOnly();
 };
 
 tst_QQuickTableView::tst_QQuickTableView()
@@ -1666,6 +1667,59 @@ void tst_QQuickTableView::checkChangingModelFromDelegate()
     QCOMPARE(tableViewPrivate->loadedTable.height(), 3);
 }
 
+void tst_QQuickTableView::checkRebuildViewportOnly()
+{
+    // Check that we only rebuild from the current top-left cell
+    // when you add or remove rows and columns. There should be
+    // no need to do a rebuild from scratch in such cases.
+    LOAD_TABLEVIEW("countingtableview.qml");
+
+    const char *propName = "delegatesCreatedCount";
+    const qreal delegateWidth = 100;
+    const qreal delegateHeight = 50;
+
+    TestModel model(100, 100);
+    tableView->setModel(QVariant::fromValue(&model));
+
+    WAIT_UNTIL_POLISHED;
+
+    // Flick to row/column 50, 50
+    tableView->setContentX(delegateWidth * 50);
+    tableView->setContentY(delegateHeight * 50);
+
+    // Set reuse items to false, just to make it easier to
+    // check the number of items created during a rebuild.
+    tableView->setReuseItems(false);
+    const int itemCountBeforeRebuild = tableViewPrivate->loadedItems.count();
+
+    // Since all cells have the same size, we expect that we end up creating
+    // the same amount of items that were already showing before, even after
+    // adding or removing rows and columns.
+    view->rootObject()->setProperty(propName, 0);
+    model.insertRow(51);
+    WAIT_UNTIL_POLISHED;
+    int countAfterRebuild = view->rootObject()->property(propName).toInt();
+    QCOMPARE(countAfterRebuild, itemCountBeforeRebuild);
+
+    view->rootObject()->setProperty(propName, 0);
+    model.removeRow(51);
+    WAIT_UNTIL_POLISHED;
+    countAfterRebuild = view->rootObject()->property(propName).toInt();
+    QCOMPARE(countAfterRebuild, itemCountBeforeRebuild);
+
+    view->rootObject()->setProperty(propName, 0);
+    model.insertColumn(51);
+    WAIT_UNTIL_POLISHED;
+    countAfterRebuild = view->rootObject()->property(propName).toInt();
+    QCOMPARE(countAfterRebuild, itemCountBeforeRebuild);
+
+    view->rootObject()->setProperty(propName, 0);
+    model.removeColumn(51);
+    WAIT_UNTIL_POLISHED;
+    countAfterRebuild = view->rootObject()->property(propName).toInt();
+    QCOMPARE(countAfterRebuild, itemCountBeforeRebuild);
+}
+
 QTEST_MAIN(tst_QQuickTableView)
 
 #include "tst_qquicktableview.moc"