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>

12 files changed, 400 insertions, 37 deletions

diff --git a/src/imports/controls/ComboBox.qml b/src/imports/controls/ComboBox.qml
index 6a885320..8d1a28be 100644
--- a/src/imports/controls/ComboBox.qml
+++ b/src/imports/controls/ComboBox.qml
@@ -80,7 +80,7 @@ T.ComboBox {
 
         enabled: control.editable
         autoScroll: control.editable
-        readOnly: control.popup.visible
+        readOnly: control.down
         inputMethodHints: control.inputMethodHints
         validator: control.validator
 
@@ -104,7 +104,7 @@ T.ComboBox {
         implicitHeight: 40
 
         color: !control.editable && control.visualFocus ? (control.pressed ? Default.focusPressedColor : Default.focusLightColor) :
-            (control.down || popup.visible ? Default.buttonPressedColor : Default.buttonColor)
+            (control.down ? Default.buttonPressedColor : Default.buttonColor)
         border.color: Default.focusColor
         border.width: !control.editable && control.visualFocus ? 2 : 0
         visible: !control.flat || control.down
@@ -120,7 +120,7 @@ T.ComboBox {
         contentItem: ListView {
             clip: true
             implicitHeight: contentHeight
-            model: control.popup.visible ? control.delegateModel : null
+            model: control.delegateModel
             currentIndex: control.highlightedIndex
             highlightRangeMode: ListView.ApplyRange
             highlightMoveDuration: 0
diff --git a/src/imports/controls/material/ComboBox.qml b/src/imports/controls/material/ComboBox.qml
index da9fd73c..d2ca7679 100644
--- a/src/imports/controls/material/ComboBox.qml
+++ b/src/imports/controls/material/ComboBox.qml
@@ -84,7 +84,7 @@ T.ComboBox {
 
         enabled: control.editable
         autoScroll: control.editable
-        readOnly: control.popup.visible
+        readOnly: control.down
         inputMethodHints: control.inputMethodHints
         validator: control.validator
 
@@ -161,7 +161,7 @@ T.ComboBox {
         contentItem: ListView {
             clip: true
             implicitHeight: contentHeight
-            model: control.popup.visible ? control.delegateModel : null
+            model: control.delegateModel
             currentIndex: control.highlightedIndex
             highlightRangeMode: ListView.ApplyRange
             highlightMoveDuration: 0
@@ -171,7 +171,7 @@ T.ComboBox {
 
         background: Rectangle {
             radius: 2
-            color: control.popup.Material.dialogColor
+            color: parent.Material.dialogColor
 
             layer.enabled: control.enabled
             layer.effect: ElevationEffect {
diff --git a/src/imports/controls/universal/ComboBox.qml b/src/imports/controls/universal/ComboBox.qml
index a2ba0236..596dcf5b 100644
--- a/src/imports/controls/universal/ComboBox.qml
+++ b/src/imports/controls/universal/ComboBox.qml
@@ -91,7 +91,7 @@ T.ComboBox {
 
         enabled: control.editable
         autoScroll: control.editable
-        readOnly: control.popup.visible
+        readOnly: control.down
         inputMethodHints: control.inputMethodHints
         validator: control.validator
 
@@ -111,7 +111,7 @@ T.ComboBox {
         border.width: control.flat ? 0 : 2 // ComboBoxBorderThemeThickness
         border.color: !control.enabled ? control.Universal.baseLowColor :
                        control.editable && control.activeFocus ? control.Universal.accent :
-                       control.down || popup.visible ? control.Universal.baseMediumLowColor :
+                       control.down ? control.Universal.baseMediumLowColor :
                        control.hovered ? control.Universal.baseMediumColor : control.Universal.baseMediumLowColor
         color: !control.enabled ? control.Universal.baseLowColor :
                 control.down ? control.Universal.listMediumColor :
@@ -143,7 +143,7 @@ T.ComboBox {
         contentItem: ListView {
             clip: true
             implicitHeight: contentHeight
-            model: control.popup.visible ? control.delegateModel : null
+            model: control.delegateModel
             currentIndex: control.highlightedIndex
             highlightRangeMode: ListView.ApplyRange
             highlightMoveDuration: 0
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)
diff --git a/src/quicktemplates2/qquickcombobox_p.h b/src/quicktemplates2/qquickcombobox_p.h
index 030d068b..7c27ca99 100644
--- a/src/quicktemplates2/qquickcombobox_p.h
+++ b/src/quicktemplates2/qquickcombobox_p.h
@@ -82,6 +82,7 @@ class Q_QUICKTEMPLATES2_PRIVATE_EXPORT QQuickComboBox : public QQuickControl
     Q_PROPERTY(Qt::InputMethodHints inputMethodHints READ inputMethodHints WRITE setInputMethodHints NOTIFY inputMethodHintsChanged FINAL REVISION 2)
     Q_PROPERTY(bool inputMethodComposing READ isInputMethodComposing NOTIFY inputMethodComposingChanged FINAL REVISION 2)
     Q_PROPERTY(bool acceptableInput READ hasAcceptableInput NOTIFY acceptableInputChanged FINAL REVISION 2)
+    Q_CLASSINFO("DeferredPropertyNames", "background,contentItem,indicator,popup")
 
 public:
     explicit QQuickComboBox(QQuickItem *parent = nullptr);
diff --git a/tests/auto/auto.pro b/tests/auto/auto.pro
index 17613796..4660a695 100644
--- a/tests/auto/auto.pro
+++ b/tests/auto/auto.pro
@@ -24,7 +24,7 @@ SUBDIRS += \
     snippets
 
 # QTBUG-60268
-boot2qt: SUBDIRS -= qquickapplicationwindow calendar controls cursor \
+boot2qt: SUBDIRS -= qquickapplicationwindow calendar controls cursor customization \
                     qquickdrawer focus font qquickmenu platform qquickpopup qquickmaterialstyle \
                     qquickmaterialstyleconf qquickuniversalstyle \
                     qquickuniversalstyleconf snippets
diff --git a/tests/auto/controls/data/tst_combobox.qml b/tests/auto/controls/data/tst_combobox.qml
index abdfd51a..00e1a2cc 100644
--- a/tests/auto/controls/data/tst_combobox.qml
+++ b/tests/auto/controls/data/tst_combobox.qml
@@ -1466,7 +1466,6 @@ TestCase {
         var control = createTemporaryObject(comboBox, testCase, { model: 1 })
         verify(control)
         compare(control.popup.implicitHeight, 0)
-        compare(control.popup.height, 0)
 
         // Ensure that it's open so that the popup's implicitHeight changes when we increase the model count.
         control.popup.open()
diff --git a/tests/auto/customization/data/styles/empty/ComboBox.qml b/tests/auto/customization/data/styles/empty/ComboBox.qml
new file mode 100644
index 00000000..5e7e9b14
--- /dev/null
+++ b/tests/auto/customization/data/styles/empty/ComboBox.qml
@@ -0,0 +1,57 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** 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.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+import QtQuick 2.9
+import QtQuick.Templates 2.2 as T
+
+T.ComboBox {
+    id: control
+    objectName: "combobox-empty"
+}
diff --git a/tests/auto/customization/data/styles/incomplete/ComboBox.qml b/tests/auto/customization/data/styles/incomplete/ComboBox.qml
new file mode 100644
index 00000000..7dd92b74
--- /dev/null
+++ b/tests/auto/customization/data/styles/incomplete/ComboBox.qml
@@ -0,0 +1,61 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** 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.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+import QtQuick 2.9
+import QtQuick.Templates 2.2 as T
+
+T.ComboBox {
+    id: control
+    objectName: "combobox-incomplete"
+
+    contentItem: Item {
+        objectName: "combobox-contentItem-incomplete"
+    }
+}
diff --git a/tests/auto/customization/data/styles/override/ComboBox.qml b/tests/auto/customization/data/styles/override/ComboBox.qml
new file mode 100644
index 00000000..e87a4640
--- /dev/null
+++ b/tests/auto/customization/data/styles/override/ComboBox.qml
@@ -0,0 +1,61 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** 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.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+import QtQuick 2.9
+import "../simple" as Simple
+
+Simple.ComboBox {
+    id: control
+    objectName: "combobox-override"
+
+    background: Rectangle {
+        objectName: "combobox-background-override"
+    }
+}
diff --git a/tests/auto/customization/data/styles/simple/ComboBox.qml b/tests/auto/customization/data/styles/simple/ComboBox.qml
new file mode 100644
index 00000000..ac46cf62
--- /dev/null
+++ b/tests/auto/customization/data/styles/simple/ComboBox.qml
@@ -0,0 +1,81 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** 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.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+import QtQuick 2.9
+import QtQuick.Templates 2.2 as T
+
+T.ComboBox {
+    id: control
+    objectName: "combobox-simple"
+
+    implicitWidth: Math.max(contentItem.implicitWidth, background.implicitWidth)
+    implicitHeight: Math.max(contentItem.implicitHeight, background.implicitHeight)
+
+    indicator: Text {
+        objectName: "combobox-indicator-simple"
+        text: control.comboed ? "V" : ""
+    }
+
+    contentItem: Text {
+        objectName: "combobox-contentItem-simple"
+        text: control.currentText
+    }
+
+    background: Rectangle {
+        objectName: "combobox-background-simple"
+        implicitWidth: 20
+        implicitHeight: 20
+        color: control.down ? "red" : "green"
+    }
+
+    popup: T.Popup {
+        objectName: "combobox-popup-simple"
+    }
+}
diff --git a/tests/auto/customization/tst_customization.cpp b/tests/auto/customization/tst_customization.cpp
index 20914b61..51ae3650 100644
--- a/tests/auto/customization/tst_customization.cpp
+++ b/tests/auto/customization/tst_customization.cpp
@@ -39,6 +39,8 @@
 #include <QtCore/qregularexpression.h>
 #include <QtQml/qqmlengine.h>
 #include <QtQml/qqmlcomponent.h>
+#include <QtQuick/qquickitem.h>
+#include <QtQuick/qquickwindow.h>
 #include <QtQuickControls2/qquickstyle.h>
 #include "../shared/visualtestutil.h"
 
@@ -55,6 +57,8 @@ private slots:
     void creation_data();
     void creation();
 
+    void comboPopup();
+
 private:
     void reset();
     void addHooks();
@@ -131,6 +135,7 @@ void tst_customization::creation_data()
     QTest::newRow("empty:ApplicationWindow") << "empty" << "ApplicationWindow"<< (QStringList() << "applicationwindow-empty");
     QTest::newRow("empty:Button") << "empty" << "Button"<< (QStringList() << "button-empty");
     QTest::newRow("empty:CheckBox") << "empty" << "CheckBox" << (QStringList() << "checkbox-empty");
+    QTest::newRow("empty:ComboBox") << "empty" << "ComboBox" << (QStringList() << "combobox-empty");
     QTest::newRow("empty:Dial") << "empty" << "Dial" << (QStringList() << "dial-empty");
     QTest::newRow("empty:Label") << "empty" << "Label"<< (QStringList() << "label-empty");
     QTest::newRow("empty:RadioButton") << "empty" << "RadioButton" << (QStringList() << "radiobutton-empty");
@@ -142,6 +147,7 @@ void tst_customization::creation_data()
     // the "incomplete" style is missing most delegates
     QTest::newRow("incomplete:Button") << "incomplete" << "Button" << (QStringList() << "button-incomplete" << "button-background-incomplete");
     QTest::newRow("incomplete:CheckBox") << "incomplete" << "CheckBox" << (QStringList() << "checkbox-incomplete" << "checkbox-contentItem-incomplete");
+    QTest::newRow("incomplete:ComboBox") << "incomplete" << "ComboBox" << (QStringList() << "combobox-incomplete" << "combobox-contentItem-incomplete");
     QTest::newRow("incomplete:Dial") << "incomplete" << "Dial" << (QStringList() << "dial-incomplete" << "dial-handle-incomplete");
     QTest::newRow("incomplete:RadioButton") << "incomplete" << "RadioButton" << (QStringList() << "radiobutton-incomplete" << "radiobutton-indicator-incomplete");
     QTest::newRow("incomplete:RangeSlider") << "incomplete" << "RangeSlider" << (QStringList() << "rangeslider-incomplete" << "rangeslider-first-handle-incomplete" << "rangeslider-second-handle-incomplete");
@@ -151,6 +157,7 @@ void tst_customization::creation_data()
     QTest::newRow("simple:ApplicationWindow") << "simple" << "ApplicationWindow" << (QStringList() << "applicationwindow-simple" << "applicationwindow-background-simple");
     QTest::newRow("simple:Button") << "simple" << "Button" << (QStringList() << "button-simple" << "button-background-simple" << "button-contentItem-simple");
     QTest::newRow("simple:CheckBox") << "simple" << "CheckBox" << (QStringList() << "checkbox-simple" << "checkbox-contentItem-simple" << "checkbox-indicator-simple");
+    QTest::newRow("simple:ComboBox") << "simple" << "ComboBox" << (QStringList() << "combobox-simple" << "combobox-background-simple" << "combobox-contentItem-simple" << "combobox-indicator-simple");
     QTest::newRow("simple:Dial") << "simple" << "Dial" << (QStringList() << "dial-simple" << "dial-background-simple" << "dial-handle-simple");
     QTest::newRow("simple:Label") << "simple" << "Label" << (QStringList() << "label-simple" << "label-background-simple");
     QTest::newRow("simple:RadioButton") << "simple" << "RadioButton" << (QStringList() << "radiobutton-simple" << "radiobutton-contentItem-simple" << "radiobutton-indicator-simple");
@@ -163,6 +170,7 @@ void tst_customization::creation_data()
     QTest::newRow("override:ApplicationWindow") << "override" << "ApplicationWindow" << (QStringList() << "applicationwindow-override" << "applicationwindow-background-override" << "applicationwindow-simple"); // overrides "simple"
     QTest::newRow("override:Button") << "override" << "Button" << (QStringList() << "button-override" << "button-background-override" << "button-contentItem-override" << "button-empty"); // overrides "empty"
     QTest::newRow("override:CheckBox") << "override" << "CheckBox" << (QStringList() << "checkbox-override" << "checkbox-background-override" << "checkbox-contentItem-incomplete" << "checkbox-incomplete"); // overrides "incomplete"
+    QTest::newRow("override:ComboBox") << "override" << "ComboBox" << (QStringList() << "combobox-override" << "combobox-background-override" << "combobox-contentItem-simple"  << "combobox-indicator-simple" << "combobox-simple"); // overrides "simple"
     QTest::newRow("override:Dial") << "override" << "Dial" << (QStringList() << "dial-override"  << "dial-background-override" << "dial-handle-override" << "dial-incomplete"); // overrides "incomplete"
     QTest::newRow("override:Label") << "override" << "Label" << (QStringList() << "label-override" << "label-background-override" << "label-simple"); // overrides "simple"
     QTest::newRow("override:RadioButton") << "override" << "RadioButton" << (QStringList() << "radiobutton-override"  << "radiobutton-background-override" << "radiobutton-contentItem-simple" << "radiobutton-indicator-override" << "radiobutton-simple"); // overrides "simple"
@@ -190,6 +198,47 @@ void tst_customization::creation()
     QVERIFY2(qt_destroyedQObjects()->isEmpty(), qPrintable("unexpectedly destroyed: " + qt_destroyedQObjects->join(", ") + " were unexpectedly destroyed"));
 }
 
+void tst_customization::comboPopup()
+{
+    QQuickStyle::setStyle(testFile("styles/simple"));
+
+    {
+        // test that ComboBox::popup is created when accessed
+        QQmlComponent component(engine);
+        component.setData("import QtQuick.Controls 2.2; ComboBox { }", QUrl());
+        QScopedPointer<QQuickItem> comboBox(qobject_cast<QQuickItem *>(component.create()));
+        QVERIFY(comboBox);
+
+        QVERIFY(!qt_createdQObjects()->contains("combobox-popup-simple"));
+
+        QObject *popup = comboBox->property("popup").value<QObject *>();
+        QVERIFY(popup);
+        QVERIFY(qt_createdQObjects()->contains("combobox-popup-simple"));
+    }
+
+    reset();
+
+    {
+        // test that ComboBox::popup is created when it becomes visible
+        QQuickWindow window;
+        window.resize(300, 300);
+        window.show();
+        window.requestActivate();
+        QVERIFY(QTest::qWaitForWindowActive(&window));
+
+        QQmlComponent component(engine);
+        component.setData("import QtQuick.Controls 2.2; ComboBox { }", QUrl());
+        QScopedPointer<QQuickItem> comboBox(qobject_cast<QQuickItem *>(component.create()));
+        QVERIFY(comboBox);
+
+        comboBox->setParentItem(window.contentItem());
+        QVERIFY(!qt_createdQObjects()->contains("combobox-popup-simple"));
+
+        QTest::mouseClick(&window, Qt::LeftButton, Qt::NoModifier, QPoint(1, 1));
+        QVERIFY(qt_createdQObjects()->contains("combobox-popup-simple"));
+    }
+}
+
 QTEST_MAIN(tst_customization)
 
 #include "tst_customization.moc"