QQuickTableView: implement support for reusing delegate items

This patch will make use of the recent changes in QQmlTableInstanceModel
to support reusing delegate items.

The API in TableView to enable this will mainly be a new property
"reuseItems". This property is true by default. By setting it to
false, reusing items will never happen.

When an item is reused, the signal "TableView.reused" is
emitted after the fact, in case the delegate item needs to
execute some extra code during the process. Likewise, a signal
"TableView.pooled" is emitted when the item is pooled.

From an implementation point of view, TableView only need to
do two things to enable reusing of items. First, whenever it releases
items, it provides a second argument to release(), informing
QQmlTableInstanceModel if the item can be reused. Second, it
needs to call drainReusePool() at appropriate times to ensure
that no item will be kept alive in the pool for too long.

Change-Id: I830e2eace776302ac58946733566208aa8954159
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

3 files changed, 306 insertions, 11 deletions

diff --git a/tests/auto/quick/qquicktableview/data/countingtableview.qml b/tests/auto/quick/qquicktableview/data/countingtableview.qml
index 1e8e9f43fb..c736d570b8 100644
--- a/tests/auto/quick/qquicktableview/data/countingtableview.qml
+++ b/tests/auto/quick/qquicktableview/data/countingtableview.qml
@@ -47,8 +47,13 @@ Item {
     height: 450
 
     property alias tableView: tableView
+
+    // currentDelegateCount is the number of currently visible items
     property int currentDelegateCount: 0
+    // maxDelegateCount is the largest number of items that has ever been visible at the same time
     property int maxDelegateCount: 0
+    // delegatesCreatedCount is the number of items created during the lifetime of the test
+    property int delegatesCreatedCount: 0
 
     TableView {
         id: tableView
@@ -68,11 +73,18 @@ Item {
             implicitHeight: 50
             color: "lightgray"
             border.width: 1
+
+            property int pooledCount: 0
+            property int reusedCount: 0
+            TableView.onPooled: pooledCount++;
+            TableView.onReused: reusedCount++;
+
             Text {
                 anchors.centerIn: parent
-                text: modelData
+                text: column
             }
             Component.onCompleted: {
+                delegatesCreatedCount++;
                 currentDelegateCount++;
                 maxDelegateCount = Math.max(maxDelegateCount, currentDelegateCount);
             }
diff --git a/tests/auto/quick/qquicktableview/data/qqmllistpropertymodel.qml b/tests/auto/quick/qquicktableview/data/qqmllistpropertymodel.qml
new file mode 100644
index 0000000000..c866af8526
--- /dev/null
+++ b/tests/auto/quick/qquicktableview/data/qqmllistpropertymodel.qml
@@ -0,0 +1,85 @@
+/****************************************************************************
+**
+** 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
+import Qt.labs.tableview 1.0
+
+Item {
+    id: root
+    width: 640
+    height: 450
+
+    property alias tableView: tableView
+
+    TableView {
+        id: tableView
+        width: 600
+        height: 400
+        anchors.margins: 1
+        clip: true
+        delegate: tableViewDelegate
+        cacheBuffer: 0
+    }
+
+    Item {
+        Repeater {
+            model: 100
+            Item { property string someCustomProperty: index }
+        }
+        Component.onCompleted: tableView.model = children
+    }
+
+    Component {
+        id: tableViewDelegate
+        Rectangle {
+            objectName: "tableViewDelegate"
+            implicitWidth: 100
+            implicitHeight: 50
+            color: "lightgray"
+            border.width: 1
+
+            Text {
+                anchors.centerIn: parent
+                text: column
+            }
+        }
+    }
+
+}
diff --git a/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp b/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp
index 1cedde4f79..86839b61dc 100644
--- a/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp
+++ b/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp
@@ -50,6 +50,7 @@ using namespace QQuickVisualTestUtil;
 
 static const char* kTableViewPropName = "tableView";
 static const char* kDelegateObjectName = "tableViewDelegate";
+static const char *kDelegatesCreatedCountProp = "delegatesCreatedCount";
 
 Q_DECLARE_METATYPE(QMarginsF);
 
@@ -112,6 +113,12 @@ private slots:
     void flickOvershoot();
     void checkRowColumnCount();
     void modelSignals();
+    void checkIfDelegatesAreReused_data();
+    void checkIfDelegatesAreReused();
+    void checkContextProperties_data();
+    void checkContextProperties();
+    void checkContextPropertiesQQmlListProperyModel_data();
+    void checkContextPropertiesQQmlListProperyModel();
 };
 
 tst_QQuickTableView::tst_QQuickTableView()
@@ -757,11 +764,16 @@ void tst_QQuickTableView::flick_data()
 {
     QTest::addColumn<QSizeF>("spacing");
     QTest::addColumn<QMarginsF>("margins");
-
-    QTest::newRow("s:0 m:0") << QSizeF(0, 0) << QMarginsF(0, 0, 0, 0);
-    QTest::newRow("s:5 m:0") << QSizeF(5, 5) << QMarginsF(0, 0, 0, 0);
-    QTest::newRow("s:0 m:20") << QSizeF(0, 0) << QMarginsF(20, 20, 20, 20);
-    QTest::newRow("s:5 m:20") << QSizeF(5, 5) << QMarginsF(20, 20, 20, 20);
+    QTest::addColumn<bool>("reuseItems");
+
+    QTest::newRow("s:0 m:0 reuse") << QSizeF(0, 0) << QMarginsF(0, 0, 0, 0) << true;
+    QTest::newRow("s:5 m:0 reuse") << QSizeF(5, 5) << QMarginsF(0, 0, 0, 0) << true;
+    QTest::newRow("s:0 m:20 reuse") << QSizeF(0, 0) << QMarginsF(20, 20, 20, 20) << true;
+    QTest::newRow("s:5 m:20 reuse") << QSizeF(5, 5) << QMarginsF(20, 20, 20, 20) << true;
+    QTest::newRow("s:0 m:0") << QSizeF(0, 0) << QMarginsF(0, 0, 0, 0) << false;
+    QTest::newRow("s:5 m:0") << QSizeF(5, 5) << QMarginsF(0, 0, 0, 0) << false;
+    QTest::newRow("s:0 m:20") << QSizeF(0, 0) << QMarginsF(20, 20, 20, 20) << false;
+    QTest::newRow("s:5 m:20") << QSizeF(5, 5) << QMarginsF(20, 20, 20, 20) << false;
 }
 
 void tst_QQuickTableView::flick()
@@ -770,6 +782,7 @@ void tst_QQuickTableView::flick()
     // with different table configurations.
     QFETCH(QSizeF, spacing);
     QFETCH(QMarginsF, margins);
+    QFETCH(bool, reuseItems);
     LOAD_TABLEVIEW("plaintableview.qml");
 
     const qreal delegateWidth = 100;
@@ -788,6 +801,7 @@ void tst_QQuickTableView::flick()
     tableView->setRightMargin(margins.right());
     tableView->setBottomMargin(margins.bottom());
     tableView->setCacheBuffer(0);
+    tableView->setReuseItems(reuseItems);
     tableView->setWidth(margins.left() + (visualColumnCount * cellWidth) - spacing.width());
     tableView->setHeight(margins.top() + (visualRowCount * cellHeight) - spacing.height());
 
@@ -821,11 +835,16 @@ void tst_QQuickTableView::flickOvershoot_data()
 {
     QTest::addColumn<QSizeF>("spacing");
     QTest::addColumn<QMarginsF>("margins");
-
-    QTest::newRow("s:0 m:0") << QSizeF(0, 0) << QMarginsF(0, 0, 0, 0);
-    QTest::newRow("s:5 m:0") << QSizeF(5, 5) << QMarginsF(0, 0, 0, 0);
-    QTest::newRow("s:0 m:20") << QSizeF(0, 0) << QMarginsF(20, 20, 20, 20);
-    QTest::newRow("s:5 m:20") << QSizeF(5, 5) << QMarginsF(20, 20, 20, 20);
+    QTest::addColumn<bool>("reuseItems");
+
+    QTest::newRow("s:0 m:0 reuse") << QSizeF(0, 0) << QMarginsF(0, 0, 0, 0) << true;
+    QTest::newRow("s:5 m:0 reuse") << QSizeF(5, 5) << QMarginsF(0, 0, 0, 0) << true;
+    QTest::newRow("s:0 m:20 reuse") << QSizeF(0, 0) << QMarginsF(20, 20, 20, 20) << true;
+    QTest::newRow("s:5 m:20 reuse") << QSizeF(5, 5) << QMarginsF(20, 20, 20, 20) << true;
+    QTest::newRow("s:0 m:0") << QSizeF(0, 0) << QMarginsF(0, 0, 0, 0) << false;
+    QTest::newRow("s:5 m:0") << QSizeF(5, 5) << QMarginsF(0, 0, 0, 0) << false;
+    QTest::newRow("s:0 m:20") << QSizeF(0, 0) << QMarginsF(20, 20, 20, 20) << false;
+    QTest::newRow("s:5 m:20") << QSizeF(5, 5) << QMarginsF(20, 20, 20, 20) << false;
 }
 
 void tst_QQuickTableView::flickOvershoot()
@@ -836,6 +855,7 @@ void tst_QQuickTableView::flickOvershoot()
     // when everything is flicked out of view.
     QFETCH(QSizeF, spacing);
     QFETCH(QMarginsF, margins);
+    QFETCH(bool, reuseItems);
     LOAD_TABLEVIEW("plaintableview.qml");
 
     const int rowCount = 5;
@@ -857,6 +877,7 @@ void tst_QQuickTableView::flickOvershoot()
     tableView->setRightMargin(margins.right());
     tableView->setBottomMargin(margins.bottom());
     tableView->setCacheBuffer(0);
+    tableView->setReuseItems(reuseItems);
     tableView->setWidth(tableWidth - margins.right() - cellWidth / 2);
     tableView->setHeight(tableHeight - margins.bottom() - cellHeight / 2);
 
@@ -1092,6 +1113,183 @@ void tst_QQuickTableView::modelSignals()
     QCOMPARE(tableView->columns(), 1);
 }
 
+void tst_QQuickTableView::checkIfDelegatesAreReused_data()
+{
+    QTest::addColumn<bool>("reuseItems");
+
+    QTest::newRow("reuse = true") << true;
+    QTest::newRow("reuse = false") << false;
+}
+
+void tst_QQuickTableView::checkIfDelegatesAreReused()
+{
+    // Check that we end up reusing delegate items while flicking if
+    // TableView has reuseItems set to true, but otherwise not.
+    QFETCH(bool, reuseItems);
+    LOAD_TABLEVIEW("countingtableview.qml");
+
+    const qreal delegateWidth = 100;
+    const int pageFlickCount = 1;
+
+    auto model = TestModelAsVariant(100, 100);
+    tableView->setModel(model);
+    tableView->setReuseItems(reuseItems);
+
+    // Flick half an item to the left, to force one extra column to load before we start.
+    // This will make things less complicated below, when checking how many times the items
+    // have been reused (all items will then report the same number).
+    tableView->setContentX(delegateWidth / 2);
+    tableView->polish();
+
+    WAIT_UNTIL_POLISHED;
+
+    const int visibleColumnCount = tableViewPrivate->loadedTable.width();
+    const int visibleRowCount = tableViewPrivate->loadedTable.height();
+    const int delegateCountAfterInit = view->rootObject()->property(kDelegatesCreatedCountProp).toInt();
+
+    for (int column = 1; column <= (visibleColumnCount * pageFlickCount); ++column) {
+        // Flick columns to the left (and add one pixel to ensure the left column is completely out)
+        tableView->setContentX((delegateWidth * column) + 1);
+        tableView->polish();
+
+        WAIT_UNTIL_POLISHED;
+
+        // Check that the number of delegate items created so far is what we expect.
+        const int delegatesCreatedCount = view->rootObject()->property(kDelegatesCreatedCountProp).toInt();
+        int expectedCount = delegateCountAfterInit + (reuseItems ? 0 : visibleRowCount * column);
+        QCOMPARE(delegatesCreatedCount, expectedCount);
+    }
+
+    // Check that each delegate item has been reused as many times
+    // as we have flicked pages (if reuse is enabled).
+    for (auto fxItem : tableViewPrivate->loadedItems) {
+        int pooledCount = fxItem->item->property("pooledCount").toInt();
+        int reusedCount = fxItem->item->property("reusedCount").toInt();
+        if (reuseItems) {
+            QCOMPARE(pooledCount, pageFlickCount);
+            QCOMPARE(reusedCount, pageFlickCount);
+        } else {
+            QCOMPARE(pooledCount, 0);
+            QCOMPARE(reusedCount, 0);
+        }
+    }
+}
+
+void tst_QQuickTableView::checkContextProperties_data()
+{
+    QTest::addColumn<QVariant>("model");
+    QTest::addColumn<bool>("reuseItems");
+
+    auto stringList = QStringList();
+    for (int i = 0; i < 100; ++i)
+        stringList.append(QString::number(i));
+
+    QTest::newRow("QAIM, reuse=false") << TestModelAsVariant(100, 100) << false;
+    QTest::newRow("QAIM, reuse=true") << TestModelAsVariant(100, 100) << true;
+    QTest::newRow("Number model, reuse=false") << QVariant::fromValue(100) << false;
+    QTest::newRow("Number model, reuse=true") << QVariant::fromValue(100) << true;
+    QTest::newRow("QStringList, reuse=false") << QVariant::fromValue(stringList) << false;
+    QTest::newRow("QStringList, reuse=true") << QVariant::fromValue(stringList) << true;
+}
+
+void tst_QQuickTableView::checkContextProperties()
+{
+    // Check that the context properties of the delegate items
+    // are what we expect while flicking, with or without item recycling.
+    QFETCH(QVariant, model);
+    QFETCH(bool, reuseItems);
+    LOAD_TABLEVIEW("countingtableview.qml");
+
+    const qreal delegateWidth = 100;
+    const qreal delegateHeight = 50;
+    const int rowCount = 100;
+    const int pageFlickCount = 3;
+
+    tableView->setModel(model);
+    tableView->setReuseItems(reuseItems);
+
+    WAIT_UNTIL_POLISHED;
+
+    const int visibleRowCount = qMin(tableView->rows(), qCeil(tableView->height() / delegateHeight));
+    const int visibleColumnCount = qMin(tableView->columns(), qCeil(tableView->width() / delegateWidth));
+
+    for (int row = 1; row <= (visibleRowCount * pageFlickCount); ++row) {
+        // Flick rows up
+        tableView->setContentY((delegateHeight * row) + (delegateHeight / 2));
+        tableView->polish();
+
+        WAIT_UNTIL_POLISHED;
+
+        for (int col = 0; col < visibleColumnCount; ++col) {
+            const auto item = tableViewPrivate->loadedTableItem(QPoint(col, row))->item;
+            const auto context = qmlContext(item.data());
+            const int contextIndex = context->contextProperty("index").toInt();
+            const int contextRow = context->contextProperty("row").toInt();
+            const int contextColumn = context->contextProperty("column").toInt();
+            const QString contextModelData = context->contextProperty("modelData").toString();
+
+            QCOMPARE(contextIndex, row + (col * rowCount));
+            QCOMPARE(contextRow, row);
+            QCOMPARE(contextColumn, col);
+            QCOMPARE(contextModelData, QStringLiteral("%1").arg(row));
+        }
+    }
+}
+
+void tst_QQuickTableView::checkContextPropertiesQQmlListProperyModel_data()
+{
+    QTest::addColumn<bool>("reuseItems");
+
+    QTest::newRow("reuse=false") << false;
+    QTest::newRow("reuse=true") << true;
+}
+
+void tst_QQuickTableView::checkContextPropertiesQQmlListProperyModel()
+{
+    // Check that the context properties of the delegate items
+    // are what we expect while flicking, with or without item recycling.
+    // This test hard-codes the model to be a QQmlListPropertyModel from
+    // within the qml file.
+    QFETCH(bool, reuseItems);
+    LOAD_TABLEVIEW("qqmllistpropertymodel.qml");
+
+    const qreal delegateWidth = 100;
+    const qreal delegateHeight = 50;
+    const int rowCount = 100;
+    const int pageFlickCount = 3;
+
+    tableView->setReuseItems(reuseItems);
+    tableView->polish();
+
+    WAIT_UNTIL_POLISHED;
+
+    const int visibleRowCount = qMin(tableView->rows(), qCeil(tableView->height() / delegateHeight));
+    const int visibleColumnCount = qMin(tableView->columns(), qCeil(tableView->width() / delegateWidth));
+
+    for (int row = 1; row <= (visibleRowCount * pageFlickCount); ++row) {
+        // Flick rows up
+        tableView->setContentY((delegateHeight * row) + (delegateHeight / 2));
+        tableView->polish();
+
+        WAIT_UNTIL_POLISHED;
+
+        for (int col = 0; col < visibleColumnCount; ++col) {
+            const auto item = tableViewPrivate->loadedTableItem(QPoint(col, row))->item;
+            const auto context = qmlContext(item.data());
+            const int contextIndex = context->contextProperty("index").toInt();
+            const int contextRow = context->contextProperty("row").toInt();
+            const int contextColumn = context->contextProperty("column").toInt();
+            const QObject *contextModelData = qvariant_cast<QObject *>(context->contextProperty("modelData"));
+            const QString modelDataProperty = contextModelData->property("someCustomProperty").toString();
+
+            QCOMPARE(contextIndex, row + (col * rowCount));
+            QCOMPARE(contextRow, row);
+            QCOMPARE(contextColumn, col);
+            QCOMPARE(modelDataProperty, QStringLiteral("%1").arg(row));
+        }
+    }
+}
+
 QTEST_MAIN(tst_QQuickTableView)
 
 #include "tst_qquicktableview.moc"