TableView: check if the model can produce items before loading

If you assign a non-empty model, the model can still return a count
of zero if something else is amiss, like the delegate being null.
So we need to do en extra check for this before we load the first
top-left item, otherwise we'll hit an assert later in the loading process.

Change-Id: I747868faf7955b8784b2957505ae03e5b1aa0b45
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

3 files changed, 50 insertions, 3 deletions

diff --git a/src/quick/items/qquicktableview.cpp b/src/quick/items/qquicktableview.cpp
index 5bc47a2b07..b3802b7694 100644
--- a/src/quick/items/qquicktableview.cpp
+++ b/src/quick/items/qquicktableview.cpp
@@ -965,6 +965,9 @@ void QQuickTableViewPrivate::loadInitialTopLeftItem()
     if (tableSize.isEmpty())
         return;
 
+    if (model->count() == 0)
+        return;
+
     // 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);
@@ -1007,8 +1010,7 @@ void QQuickTableViewPrivate::loadAndUnloadVisibleEdges()
     if (loadedItems.isEmpty()) {
         // We need at least the top-left item to be loaded before we can
         // start loading edges around it. Not having a top-left item at
-        // this point means that the model is empty (or row and and column
-        // is 0) since we have no active load request.
+        // this point means that the model is empty (or no delegate).
         return;
     }
 
@@ -1115,7 +1117,7 @@ void QQuickTableViewPrivate::updatePolish()
         endRebuildTable();
 
     if (loadedItems.isEmpty()) {
-        qCDebug(lcTableViewDelegateLifecycle()) << "no items loaded, meaning empty model or row/column == 0";
+        qCDebug(lcTableViewDelegateLifecycle()) << "no items loaded, meaning empty model or no delegate";
         return;
     }
 
diff --git a/tests/auto/quick/qquicktableview/data/plaintableview.qml b/tests/auto/quick/qquicktableview/data/plaintableview.qml
index f4457006e6..a073941faa 100644
--- a/tests/auto/quick/qquicktableview/data/plaintableview.qml
+++ b/tests/auto/quick/qquicktableview/data/plaintableview.qml
@@ -48,6 +48,7 @@ Item {
     property alias tableView: tableView
     property real delegateWidth: 100
     property real delegateHeight: 50
+    property Component delegate: tableViewDelegate
 
     TableView {
         id: tableView
diff --git a/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp b/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp
index 33437b6eac..16b3acab99 100644
--- a/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp
+++ b/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp
@@ -86,6 +86,7 @@ private slots:
     void emptyModel_data();
     void emptyModel();
     void checkZeroSizedDelegate();
+    void noDelegate();
     void countDelegateItems_data();
     void countDelegateItems();
     void checkLayoutOfEqualSizedDelegateItems_data();
@@ -208,6 +209,49 @@ void tst_QQuickTableView::checkZeroSizedDelegate()
     }
 }
 
+void tst_QQuickTableView::noDelegate()
+{
+    // Check that you can skip setting a delegate without
+    // it causing any problems (like crashing or asserting).
+    // And then set a delegate, and do a quick check that the
+    // view gets populated as expected.
+    LOAD_TABLEVIEW("plaintableview.qml");
+
+    const int rows = 5;
+    const int columns = 5;
+    auto model = TestModelAsVariant(columns, rows);
+    tableView->setModel(model);
+
+    // Start with no delegate, and check
+    // that we end up with no items in the table.
+    tableView->setDelegate(nullptr);
+
+    WAIT_UNTIL_POLISHED;
+
+    auto items = tableViewPrivate->loadedItems;
+    QVERIFY(items.isEmpty());
+
+    // Set a delegate, and check that we end
+    // up with the expected number of items.
+    auto delegate = view->rootObject()->property("delegate").value<QQmlComponent *>();
+    QVERIFY(delegate);
+    tableView->setDelegate(delegate);
+
+    WAIT_UNTIL_POLISHED;
+
+    items = tableViewPrivate->loadedItems;
+    QCOMPARE(items.count(), rows * columns);
+
+    // And then unset the delegate again, and check
+    // that we end up with no items.
+    tableView->setDelegate(nullptr);
+
+    WAIT_UNTIL_POLISHED;
+
+    items = tableViewPrivate->loadedItems;
+    QVERIFY(items.isEmpty());
+}
+
 void tst_QQuickTableView::countDelegateItems_data()
 {
     QTest::addColumn<QVariant>("model");