QQuickTableView: sync model and delegate when ready to do so

Doing (silly) things in the delegate, like:

    Component.onCompleted: TableView.view.delegate = null

will lead to a crash. The same if you change the model.
The reason is that you end up changing the model
while e.g a row is half-way loaded. Information needed for
building the row, like model size, will then be invalid.

To protect against this, we insert a "sync" phase to the
code that takes any such changes into effect at a time
when we know it's safe to do so.

Change-Id: I85a992dfc0e04ec6635b10c9768a8ddc140e09da
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

2 files changed, 128 insertions, 0 deletions

diff --git a/tests/auto/quick/qquicktableview/data/changemodelordelegateduringupdate.qml b/tests/auto/quick/qquicktableview/data/changemodelordelegateduringupdate.qml
new file mode 100644
index 0000000000..de404be63d
--- /dev/null
+++ b/tests/auto/quick/qquicktableview/data/changemodelordelegateduringupdate.qml
@@ -0,0 +1,81 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtQuick module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+import QtQuick 2.12
+import QtQuick.Window 2.3
+
+Item {
+    width: 640
+    height: 450
+
+    property alias tableView: tableView
+    property bool changeDelegate: false
+    property bool changeModel: false
+
+    TableView {
+        id: tableView
+        width: 600
+        height: 400
+        clip: true
+        delegate: tableViewDelegate
+    }
+
+    Component {
+        id: tableViewDelegate
+        Rectangle {
+            implicitWidth: 100
+            implicitHeight: 100
+            color: "lightgray"
+            border.width: 1
+
+            Text {
+                anchors.centerIn: parent
+                text: modelData
+            }
+
+            Component.onCompleted: {
+                if (changeDelegate)
+                    TableView.view.delegate = null
+                if (changeModel)
+                    TableView.view.model = null
+            }
+        }
+    }
+
+}
diff --git a/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp b/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp
index 9eb942fc93..a1951bdf90 100644
--- a/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp
+++ b/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp
@@ -106,6 +106,8 @@ private slots:
     void checkExplicitContentWidthAndHeight();
     void checkContentXY();
     void noDelegate();
+    void changeDelegateDuringUpdate();
+    void changeModelDuringUpdate();
     void countDelegateItems_data();
     void countDelegateItems();
     void checkLayoutOfEqualSizedDelegateItems_data();
@@ -664,6 +666,51 @@ void tst_QQuickTableView::noDelegate()
     QVERIFY(items.isEmpty());
 }
 
+void tst_QQuickTableView::changeDelegateDuringUpdate()
+{
+    // Check that you can change the delegate (set it to null)
+    // while the TableView is busy loading the table.
+    LOAD_TABLEVIEW("changemodelordelegateduringupdate.qml");
+
+    auto model = TestModelAsVariant(1, 1);
+    tableView->setModel(model);
+    view->rootObject()->setProperty("changeDelegate", true);
+
+    WAIT_UNTIL_POLISHED;
+
+    // We should no longer have a delegate, and no
+    // items should therefore be loaded.
+    QCOMPARE(tableView->delegate(), nullptr);
+    QCOMPARE(tableViewPrivate->loadedItems.size(), 0);
+
+    // Even if the delegate is missing, we still report
+    // the correct size of the model
+    QCOMPARE(tableView->rows(), 1);
+    QCOMPARE(tableView->columns(), 1);
+};
+
+void tst_QQuickTableView::changeModelDuringUpdate()
+{
+    // Check that you can change the model (set it to null)
+    // while the TableView is buzy loading the table.
+    LOAD_TABLEVIEW("changemodelordelegateduringupdate.qml");
+
+    auto model = TestModelAsVariant(1, 1);
+    tableView->setModel(model);
+    view->rootObject()->setProperty("changeModel", true);
+
+    WAIT_UNTIL_POLISHED;
+
+    // We should no longer have a model, and the no
+    // items should therefore be loaded.
+    QVERIFY(tableView->model().isNull());
+    QCOMPARE(tableViewPrivate->loadedItems.size(), 0);
+
+    // The empty model has no rows or columns
+    QCOMPARE(tableView->rows(), 0);
+    QCOMPARE(tableView->columns(), 0);
+};
+
 void tst_QQuickTableView::countDelegateItems_data()
 {
     QTest::addColumn<QVariant>("model");