ComboBox: use deferred execution

As a special case, ComboBox defers the execution of the popup until
the popup is either accessed or made visible. This gives a nice boost
in creation time benchmarks (20->25, ~25%). The old optimization of
setting the delegate model only when the popup is visible is no longer
needed.

Task-number: QTBUG-50992
Change-Id: Ifeaceb759ab676bb54c6bc09dc97810eade72ca1
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

1 files changed, 80 insertions, 26 deletions

diff --git a/src/quicktemplates2/qquickcombobox.cpp b/src/quicktemplates2/qquickcombobox.cpp
index d22e09d5..dde27e2a 100644
--- a/src/quicktemplates2/qquickcombobox.cpp
+++ b/src/quicktemplates2/qquickcombobox.cpp
@@ -38,6 +38,7 @@
 #include "qquickcontrol_p_p.h"
 #include "qquickabstractbutton_p.h"
 #include "qquickpopup_p_p.h"
+#include "qquickdeferredexecute_p_p.h"
 
 #include <QtCore/qregexp.h>
 #include <QtCore/qabstractitemmodel.h>
@@ -252,6 +253,11 @@ public:
     void handleRelease(const QPointF &point) override;
     void handleUngrab() override;
 
+    QQuickItem *getContentItem() override;
+
+    void executeIndicator(bool complete = false);
+    void executePopup(bool complete = false);
+
     bool flat;
     bool down;
     bool hasDown;
@@ -268,8 +274,8 @@ public:
     QQuickItem *pressedItem;
     QQmlInstanceModel *delegateModel;
     QQmlComponent *delegate;
-    QQuickItem *indicator;
-    QQuickPopup *popup;
+    QQuickDeferredPointer<QQuickItem> indicator;
+    QQuickDeferredPointer<QQuickPopup> popup;
 
     struct ExtraData {
         ExtraData()
@@ -313,6 +319,9 @@ bool QQuickComboBoxPrivate::isPopupVisible() const
 
 void QQuickComboBoxPrivate::showPopup()
 {
+    if (!popup)
+        executePopup(true);
+
     if (popup && !popup->isVisible())
         popup->open();
 }
@@ -330,13 +339,10 @@ void QQuickComboBoxPrivate::hidePopup(bool accept)
 
 void QQuickComboBoxPrivate::togglePopup(bool accept)
 {
-    if (!popup)
-        return;
-
-    if (popup->isVisible())
-        hidePopup(accept);
-    else
+    if (!popup || !popup->isVisible())
         showPopup();
+    else
+        hidePopup(accept);
 }
 
 void QQuickComboBoxPrivate::popupVisibleChanged()
@@ -366,8 +372,11 @@ void QQuickComboBoxPrivate::createdItem(int index, QObject *object)
 {
     Q_Q(QQuickComboBox);
     QQuickItem *item = qobject_cast<QQuickItem *>(object);
-    if (popup && item && !item->parentItem()) {
-        item->setParentItem(popup->contentItem());
+    if (item && !item->parentItem()) {
+        if (popup)
+            item->setParentItem(popup->contentItem());
+        else
+            item->setParentItem(q);
         QQuickItemPrivate::get(item)->setCulled(true);
     }
 
@@ -662,6 +671,41 @@ void QQuickComboBoxPrivate::handleUngrab()
     q->setPressed(false);
 }
 
+QQuickItem *QQuickComboBoxPrivate::getContentItem()
+{
+    if (!contentItem)
+        executeContentItem();
+    return contentItem;
+}
+
+static inline QString indicatorName() { return QStringLiteral("indicator"); }
+
+void QQuickComboBoxPrivate::executeIndicator(bool complete)
+{
+    Q_Q(QQuickComboBox);
+    if (indicator.wasExecuted())
+        return;
+
+    if (!indicator)
+        quickBeginDeferred(q, indicatorName(), indicator);
+    if (complete)
+        quickCompleteDeferred(q, indicatorName(), indicator);
+}
+
+static inline QString popupName() { return QStringLiteral("popup"); }
+
+void QQuickComboBoxPrivate::executePopup(bool complete)
+{
+    Q_Q(QQuickComboBox);
+    if (popup.wasExecuted())
+        return;
+
+    if (!popup)
+        quickBeginDeferred(q, popupName(), popup);
+    if (complete)
+        quickCompleteDeferred(q, popupName(), popup);
+}
+
 QQuickComboBox::QQuickComboBox(QQuickItem *parent)
     : QQuickControl(*(new QQuickComboBoxPrivate), parent)
 {
@@ -677,14 +721,13 @@ QQuickComboBox::QQuickComboBox(QQuickItem *parent)
 QQuickComboBox::~QQuickComboBox()
 {
     Q_D(QQuickComboBox);
-    // Disconnect visibleChanged() to avoid a spurious highlightedIndexChanged() signal
-    // emission during the destruction of the (visible) popup. (QTBUG-57650)
-    QObjectPrivate::disconnect(d->popup, &QQuickPopup::visibleChanged, d, &QQuickComboBoxPrivate::popupVisibleChanged);
-
-    // Delete the popup directly instead of calling setPopup(nullptr) to avoid calling
-    // destroyDelegate(popup) and potentially accessing a destroyed QML context. (QTBUG-50992)
-    delete d->popup;
-    d->popup = nullptr;
+    if (d->popup) {
+        // Disconnect visibleChanged() to avoid a spurious highlightedIndexChanged() signal
+        // emission during the destruction of the (visible) popup. (QTBUG-57650)
+        QObjectPrivate::disconnect(d->popup.data(), &QQuickPopup::visibleChanged, d, &QQuickComboBoxPrivate::popupVisibleChanged);
+        delete d->popup;
+        d->popup = nullptr;
+    }
 }
 
 /*!
@@ -969,7 +1012,9 @@ void QQuickComboBox::setDelegate(QQmlComponent* delegate)
 */
 QQuickItem *QQuickComboBox::indicator() const
 {
-    Q_D(const QQuickComboBox);
+    QQuickComboBoxPrivate *d = const_cast<QQuickComboBoxPrivate *>(d_func());
+    if (!d->indicator)
+        d->executeIndicator();
     return d->indicator;
 }
 
@@ -979,13 +1024,14 @@ void QQuickComboBox::setIndicator(QQuickItem *indicator)
     if (d->indicator == indicator)
         return;
 
-    QQuickControlPrivate::destroyDelegate(d->indicator, this);
+    delete d->indicator;
     d->indicator = indicator;
     if (indicator) {
         if (!indicator->parentItem())
             indicator->setParentItem(this);
     }
-    emit indicatorChanged();
+    if (!d->indicator.isExecuting())
+        emit indicatorChanged();
 }
 
 /*!
@@ -1003,7 +1049,9 @@ void QQuickComboBox::setIndicator(QQuickItem *indicator)
 */
 QQuickPopup *QQuickComboBox::popup() const
 {
-    Q_D(const QQuickComboBox);
+    QQuickComboBoxPrivate *d = const_cast<QQuickComboBoxPrivate *>(d_func());
+    if (!d->popup)
+        d->executePopup(isComponentComplete());
     return d->popup;
 }
 
@@ -1014,8 +1062,8 @@ void QQuickComboBox::setPopup(QQuickPopup *popup)
         return;
 
     if (d->popup) {
-        QObjectPrivate::disconnect(d->popup, &QQuickPopup::visibleChanged, d, &QQuickComboBoxPrivate::popupVisibleChanged);
-        QQuickControlPrivate::destroyDelegate(d->popup, this);
+        QObjectPrivate::disconnect(d->popup.data(), &QQuickPopup::visibleChanged, d, &QQuickComboBoxPrivate::popupVisibleChanged);
+        delete d->popup;
     }
     if (popup) {
         QQuickPopupPrivate::get(popup)->allowVerticalFlip = true;
@@ -1023,7 +1071,8 @@ void QQuickComboBox::setPopup(QQuickPopup *popup)
         QObjectPrivate::connect(popup, &QQuickPopup::visibleChanged, d, &QQuickComboBoxPrivate::popupVisibleChanged);
     }
     d->popup = popup;
-    emit popupChanged();
+    if (!d->popup.isExecuting())
+        emit popupChanged();
 }
 
 /*!
@@ -1494,7 +1543,7 @@ void QQuickComboBox::keyReleaseEvent(QKeyEvent *event)
 {
     Q_D(QQuickComboBox);
     QQuickControl::keyReleaseEvent(event);
-    if (!d->popup || event->isAutoRepeat())
+    if (event->isAutoRepeat())
         return;
 
     switch (event->key()) {
@@ -1541,6 +1590,11 @@ void QQuickComboBox::wheelEvent(QWheelEvent *event)
 void QQuickComboBox::componentComplete()
 {
     Q_D(QQuickComboBox);
+    d->executeIndicator(true);
+    d->executeBackground(true);
+    d->executeContentItem(true);
+    if (d->popup)
+        d->executePopup(true);
     QQuickControl::componentComplete();
 
     if (d->delegateModel && d->ownModel)