Windows QPA: Fix slowdown with large table/tree views with accessibility

The accessibility code for notifying focus changes related to a
table/tree view was iterating over all items to find the focused one,
which for a very large number of items could cause a major slowdown
and UI freeze. This patch avoids the issue by removing the loop and
implementing the focusChild() method in the table/tree accessibility
classes.

Fixes: QTBUG-100997
Pick-to: 6.2 6.3 5.15
Change-Id: I04c847a5e65223b7a93ab82363feb32e1ebab9f3
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/plugins/platforms/windows/uiautomation/qwindowsuiamainprovider.cpp

@@ -108,21 +108,13 @@ void QWindowsUiaMainProvider::notifyFocusChange(QAccessibleEvent *event)
 {
     if (QAccessibleInterface *accessible = event->accessibleInterface()) {
         // If this is a table/tree/list, raise event for the focused cell/item instead.
-        if (accessible->tableInterface()) {
+        if (accessible->tableInterface())
-            int count = accessible->childCount();
+            if (QAccessibleInterface *child = accessible->focusChild())
-            for (int i = 0; i < count; ++i) {
+                accessible = child;
-                QAccessibleInterface *item = accessible->child(i);
+        if (QWindowsUiaMainProvider *provider = providerForAccessible(accessible))
-                if (item && item->isValid() && item->state().focused) {
-                    accessible = item;
-                    break;
-                }
-            }
-        }
-        if (QWindowsUiaMainProvider *provider = providerForAccessible(accessible)) {
             QWindowsUiaWrapper::instance()->raiseAutomationEvent(provider, UIA_AutomationFocusChangedEventId);
     }
 }
-}
 
 void QWindowsUiaMainProvider::notifyStateChange(QAccessibleStateChangeEvent *event)
 {

src/widgets/accessible/itemviews.cpp

@@ -425,6 +425,15 @@ QAccessibleInterface *QAccessibleTable::childAt(int x, int y) const
     return nullptr;
 }
 
+QAccessibleInterface *QAccessibleTable::focusChild() const
+{
+    QModelIndex index = view()->currentIndex();
+    if (!index.isValid())
+        return nullptr;
+
+    return child(logicalIndex(index));
+}
+
 int QAccessibleTable::childCount() const
 {
     if (!view()->model())
@@ -692,6 +701,20 @@ QAccessibleInterface *QAccessibleTree::childAt(int x, int y) const
     return child(i);
 }
 
+QAccessibleInterface *QAccessibleTree::focusChild() const
+{
+    QModelIndex index = view()->currentIndex();
+    if (!index.isValid())
+        return nullptr;
+
+    const QTreeView *treeView = qobject_cast<const QTreeView*>(view());
+    int row = treeView->d_func()->viewIndex(index) + (horizontalHeader() ? 1 : 0);
+    int column = index.column();
+
+    int i = row * view()->model()->columnCount() + column;
+    return child(i);
+}
+
 int QAccessibleTree::childCount() const
 {
     const QTreeView *treeView = qobject_cast<const QTreeView*>(view());

src/widgets/accessible/itemviews_p.h

@@ -79,6 +79,7 @@ public:
     QRect rect() const override;
 
     QAccessibleInterface *childAt(int x, int y) const override;
+    QAccessibleInterface *focusChild() const override;
     int childCount() const override;
     int indexOfChild(const QAccessibleInterface *) const override;
 
@@ -154,6 +155,7 @@ public:
 
 
     QAccessibleInterface *childAt(int x, int y) const override;
+    QAccessibleInterface *focusChild() const override;
     int childCount() const override;
     QAccessibleInterface *child(int index) const override;
 

tests/auto/other/qaccessibility/tst_qaccessibility.cpp

@@ -36,6 +36,7 @@
 # include <winuser.h>
 #endif
 #include <QTest>
+#include <QSignalSpy>
 #include <QtGui>
 #include <QtWidgets>
 #include <math.h>
@@ -4118,6 +4119,112 @@ void tst_QAccessibility::focusChild()
 
         QTestAccessibility::clearEvents();
     }
+
+    {
+        auto tableView = std::make_unique<QTableWidget>(3, 3);
+
+        QSignalSpy spy(tableView.get(), SIGNAL(currentCellChanged(int,int,int,int)));
+
+        tableView->setColumnCount(3);
+        QStringList hHeader;
+        hHeader << "h1" << "h2" << "h3";
+        tableView->setHorizontalHeaderLabels(hHeader);
+
+        QStringList vHeader;
+        vHeader << "v1" << "v2" << "v3";
+        tableView->setVerticalHeaderLabels(vHeader);
+
+        for (int i = 0; i < 9; ++i) {
+            QTableWidgetItem *item = new QTableWidgetItem;
+            item->setText(QString::number(i/3) + QString(".") + QString::number(i%3));
+            tableView->setItem(i/3, i%3, item);
+        }
+
+        tableView->resize(600, 600);
+        tableView->show();
+        QVERIFY(QTest::qWaitForWindowExposed(tableView.get()));
+
+        tableView->setFocus();
+
+        QAccessibleInterface *iface = QAccessible::queryAccessibleInterface(tableView.get());
+        QVERIFY(iface);
+
+        spy.clear();
+        tableView->setCurrentCell(2, 1);
+        QTRY_COMPARE(spy.count(), 1);
+
+        QAccessibleInterface *child = iface->focusChild();
+        QVERIFY(child);
+        QCOMPARE(child->text(QAccessible::Name), QStringLiteral("2.1"));
+
+        spy.clear();
+        tableView->setCurrentCell(1, 2);
+        QTRY_COMPARE(spy.count(), 1);
+
+        child = iface->focusChild();
+        QVERIFY(child);
+        QCOMPARE(child->text(QAccessible::Name), QStringLiteral("1.2"));
+    }
+
+    {
+        auto treeView = std::make_unique<QTreeWidget>();
+
+        QSignalSpy spy(treeView.get(), SIGNAL(currentItemChanged(QTreeWidgetItem*,QTreeWidgetItem*)));
+
+        treeView->setColumnCount(2);
+        QTreeWidgetItem *header = new QTreeWidgetItem;
+        header->setText(0, "Artist");
+        header->setText(1, "Work");
+        treeView->setHeaderItem(header);
+
+        QTreeWidgetItem *root1 = new QTreeWidgetItem;
+        root1->setText(0, "Spain");
+        treeView->addTopLevelItem(root1);
+
+        QTreeWidgetItem *item1 = new QTreeWidgetItem;
+        item1->setText(0, "Picasso");
+        item1->setText(1, "Guernica");
+        root1->addChild(item1);
+
+        QTreeWidgetItem *item2 = new QTreeWidgetItem;
+        item2->setText(0, "Tapies");
+        item2->setText(1, "Ambrosia");
+        root1->addChild(item2);
+
+        QTreeWidgetItem *root2 = new QTreeWidgetItem;
+        root2->setText(0, "Austria");
+        treeView->addTopLevelItem(root2);
+
+        QTreeWidgetItem *item3 = new QTreeWidgetItem;
+        item3->setText(0, "Klimt");
+        item3->setText(1, "The Kiss");
+        root2->addChild(item3);
+
+        treeView->resize(400, 400);
+        treeView->show();
+        QVERIFY(QTest::qWaitForWindowExposed(treeView.get()));
+
+        treeView->setFocus();
+
+        QAccessibleInterface *iface = QAccessible::queryAccessibleInterface(treeView.get());
+        QVERIFY(iface);
+
+        spy.clear();
+        treeView->setCurrentItem(item2);
+        QTRY_COMPARE(spy.count(), 1);
+
+        QAccessibleInterface *child = iface->focusChild();
+        QVERIFY(child);
+        QCOMPARE(child->text(QAccessible::Name), QStringLiteral("Tapies"));
+
+        spy.clear();
+        treeView->setCurrentItem(item3);
+        QTRY_COMPARE(spy.count(), 1);
+
+        child = iface->focusChild();
+        QVERIFY(child);
+        QCOMPARE(child->text(QAccessible::Name), QStringLiteral("Klimt"));
+    }
 }