Create contentItem lazily where possible

The existence of a content item is obligatory for such controls that
alias the contentData and contentChildren properties to the data and
children properties of the content item.

Even though we created empty content items in QML to ensure one always
exists, it did not not guarantee that a content item would exist for
custom styles. Furthermore, the empty content item was unnecessarily
created and destroyed when the property was overridden for a customized
control in QML.

This change creates the content item lazily where required, ensuring
that it always exists even for custom styles, but does not create it
in case a content item is supplied from QML.

Task-number: QTBUG-54347
Task-number: QTBUG-56038
Change-Id: I714ef4f8c366f0f449b922b2c16c0ec653fbd364
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

30 files changed, 43 insertions, 66 deletions

diff --git a/src/imports/controls/Dialog.qml b/src/imports/controls/Dialog.qml
index 18760d3f..c90ae6fc 100644
--- a/src/imports/controls/Dialog.qml
+++ b/src/imports/controls/Dialog.qml
@@ -55,8 +55,6 @@ T.Dialog {
 
     padding: 12
 
-    contentItem: Item { }
-
     background: Rectangle {
         border.color: Default.frameDarkColor
     }
diff --git a/src/imports/controls/Drawer.qml b/src/imports/controls/Drawer.qml
index eca9b949..689b6240 100644
--- a/src/imports/controls/Drawer.qml
+++ b/src/imports/controls/Drawer.qml
@@ -63,10 +63,6 @@ T.Drawer {
     exit: Transition { SmoothedAnimation { velocity: 5 } }
     //! [exit]
 
-    //! [contentItem]
-    contentItem: Item { }
-    //! [contentItem]
-
     //! [background]
     background: Rectangle {
         Rectangle {
diff --git a/src/imports/controls/Frame.qml b/src/imports/controls/Frame.qml
index e1148496..ef716f72 100644
--- a/src/imports/controls/Frame.qml
+++ b/src/imports/controls/Frame.qml
@@ -50,10 +50,6 @@ T.Frame {
 
     padding: 12
 
-    //! [contentItem]
-    contentItem: Item { }
-    //! [contentItem]
-
     //! [background]
     background: Rectangle {
         color: "transparent"
diff --git a/src/imports/controls/GroupBox.qml b/src/imports/controls/GroupBox.qml
index 7a20225d..1b3afd66 100644
--- a/src/imports/controls/GroupBox.qml
+++ b/src/imports/controls/GroupBox.qml
@@ -54,10 +54,6 @@ T.GroupBox {
     padding: 12
     topPadding: padding + (label && label.implicitWidth > 0 ? label.implicitHeight + spacing : 0)
 
-    //! [contentItem]
-    contentItem: Item { }
-    //! [contentItem]
-
     //! [label]
     label: Text {
         x: control.leftPadding
diff --git a/src/imports/controls/Page.qml b/src/imports/controls/Page.qml
index 1abb06a3..39080de7 100644
--- a/src/imports/controls/Page.qml
+++ b/src/imports/controls/Page.qml
@@ -42,10 +42,6 @@ import QtQuick.Templates 2.1 as T
 T.Page {
     id: control
 
-    //! [contentItem]
-    contentItem: Item { }
-    //! [contentItem]
-
     //! [background]
     background: Rectangle {
         color: Default.backgroundColor
diff --git a/src/imports/controls/Pane.qml b/src/imports/controls/Pane.qml
index 7066560a..3f6e43a9 100644
--- a/src/imports/controls/Pane.qml
+++ b/src/imports/controls/Pane.qml
@@ -50,10 +50,6 @@ T.Pane {
 
     padding: 12
 
-    //! [contentItem]
-    contentItem: Item { }
-    //! [contentItem]
-
     //! [background]
     background: Rectangle {
         color: Default.backgroundColor
diff --git a/src/imports/controls/Popup.qml b/src/imports/controls/Popup.qml
index c9e9d60e..92ac19ed 100644
--- a/src/imports/controls/Popup.qml
+++ b/src/imports/controls/Popup.qml
@@ -52,8 +52,6 @@ T.Popup {
 
     padding: 12
 
-    contentItem: Item { }
-
     background: Rectangle {
         border.color: Default.frameDarkColor
     }
diff --git a/src/imports/controls/ToolBar.qml b/src/imports/controls/ToolBar.qml
index 70c61c78..cc61a95b 100644
--- a/src/imports/controls/ToolBar.qml
+++ b/src/imports/controls/ToolBar.qml
@@ -48,10 +48,6 @@ T.ToolBar {
     contentWidth: contentItem.implicitWidth || (contentChildren.length === 1 ? contentChildren[0].implicitWidth : 0)
     contentHeight: contentItem.implicitHeight || (contentChildren.length === 1 ? contentChildren[0].implicitHeight : 0)
 
-    //! [contentItem]
-    contentItem: Item { }
-    //! [contentItem]
-
     //! [background]
     background: Rectangle {
         implicitHeight: 40
diff --git a/src/imports/controls/material/Dialog.qml b/src/imports/controls/material/Dialog.qml
index 55ff671b..8141eb8c 100644
--- a/src/imports/controls/material/Dialog.qml
+++ b/src/imports/controls/material/Dialog.qml
@@ -70,8 +70,6 @@ T.Dialog {
         NumberAnimation { property: "opacity"; from: 1.0; to: 0.0; easing.type: Easing.OutCubic; duration: 150 }
     }
 
-    contentItem: Item { }
-
     background: Rectangle {
         radius: 2
         color: control.Material.dialogColor
diff --git a/src/imports/controls/material/Drawer.qml b/src/imports/controls/material/Drawer.qml
index efb394d1..d6603b04 100644
--- a/src/imports/controls/material/Drawer.qml
+++ b/src/imports/controls/material/Drawer.qml
@@ -53,8 +53,6 @@ T.Drawer {
     enter: Transition { SmoothedAnimation { velocity: 5 } }
     exit: Transition { SmoothedAnimation { velocity: 5 } }
 
-    contentItem: Item { }
-
     background: Rectangle {
         color: control.Material.dialogColor
 
diff --git a/src/imports/controls/material/Frame.qml b/src/imports/controls/material/Frame.qml
index 4c8b7f01..45b8b263 100644
--- a/src/imports/controls/material/Frame.qml
+++ b/src/imports/controls/material/Frame.qml
@@ -50,8 +50,6 @@ T.Frame {
 
     padding: 12
 
-    contentItem: Item { }
-
     background: Rectangle {
         radius: 2
         color: control.Material.elevation > 0 ? control.Material.backgroundColor : "transparent"
diff --git a/src/imports/controls/material/GroupBox.qml b/src/imports/controls/material/GroupBox.qml
index 48827792..945c5a8c 100644
--- a/src/imports/controls/material/GroupBox.qml
+++ b/src/imports/controls/material/GroupBox.qml
@@ -54,8 +54,6 @@ T.GroupBox {
     padding: 12
     topPadding: padding + (label && label.implicitWidth > 0 ? label.implicitHeight + spacing : 0)
 
-    contentItem: Item {}
-
     label: Text {
         x: control.leftPadding
         width: control.availableWidth
diff --git a/src/imports/controls/material/Page.qml b/src/imports/controls/material/Page.qml
index f829788e..887a139d 100644
--- a/src/imports/controls/material/Page.qml
+++ b/src/imports/controls/material/Page.qml
@@ -41,8 +41,6 @@ import QtQuick.Controls.Material 2.1
 T.Page {
     id: control
 
-    contentItem: Item { }
-
     background: Rectangle {
         color: control.Material.backgroundColor
     }
diff --git a/src/imports/controls/material/Pane.qml b/src/imports/controls/material/Pane.qml
index d9828a2a..95e0a8c2 100644
--- a/src/imports/controls/material/Pane.qml
+++ b/src/imports/controls/material/Pane.qml
@@ -50,8 +50,6 @@ T.Pane {
 
     padding: 12
 
-    contentItem: Item { }
-
     background: Rectangle {
         color: control.Material.backgroundColor
         radius: control.Material.elevation > 0 ? 2 : 0
diff --git a/src/imports/controls/material/Popup.qml b/src/imports/controls/material/Popup.qml
index 2cd85846..2654aaf4 100644
--- a/src/imports/controls/material/Popup.qml
+++ b/src/imports/controls/material/Popup.qml
@@ -66,8 +66,6 @@ T.Popup {
         NumberAnimation { property: "opacity"; from: 1.0; to: 0.0; easing.type: Easing.OutCubic; duration: 150 }
     }
 
-    contentItem: Item { }
-
     background: Rectangle {
         radius: 2
         color: control.Material.dialogColor
diff --git a/src/imports/controls/material/ToolBar.qml b/src/imports/controls/material/ToolBar.qml
index 0da814f1..ac6e8bf3 100644
--- a/src/imports/controls/material/ToolBar.qml
+++ b/src/imports/controls/material/ToolBar.qml
@@ -52,8 +52,6 @@ T.ToolBar {
 
     Material.foreground: Material.toolTextColor
 
-    contentItem: Item { }
-
     background: Rectangle {
         implicitHeight: 48
         color: control.Material.toolBarColor
diff --git a/src/imports/controls/universal/Dialog.qml b/src/imports/controls/universal/Dialog.qml
index 1a2d6839..bda9bbb1 100644
--- a/src/imports/controls/universal/Dialog.qml
+++ b/src/imports/controls/universal/Dialog.qml
@@ -57,8 +57,6 @@ T.Dialog {
     topPadding: 18
     bottomPadding: 0
 
-    contentItem: Item { }
-
     background: Rectangle {
         color: control.Universal.chromeMediumLowColor
         border.color: control.Universal.chromeHighColor
diff --git a/src/imports/controls/universal/Drawer.qml b/src/imports/controls/universal/Drawer.qml
index c3dece6e..846d7031 100644
--- a/src/imports/controls/universal/Drawer.qml
+++ b/src/imports/controls/universal/Drawer.qml
@@ -57,8 +57,6 @@ T.Drawer {
     enter: Transition { SmoothedAnimation { velocity: 5 } }
     exit: Transition { SmoothedAnimation { velocity: 5 } }
 
-    contentItem: Item { }
-
     background: Rectangle {
         color: control.Universal.chromeMediumLowColor
         Rectangle {
diff --git a/src/imports/controls/universal/Frame.qml b/src/imports/controls/universal/Frame.qml
index 8c0118b0..9bd34292 100644
--- a/src/imports/controls/universal/Frame.qml
+++ b/src/imports/controls/universal/Frame.qml
@@ -49,8 +49,6 @@ T.Frame {
 
     padding: 12
 
-    contentItem: Item { }
-
     background: Rectangle {
         color: "transparent"
         border.color: control.Universal.chromeDisabledLowColor
diff --git a/src/imports/controls/universal/GroupBox.qml b/src/imports/controls/universal/GroupBox.qml
index fea4efae..d45505c7 100644
--- a/src/imports/controls/universal/GroupBox.qml
+++ b/src/imports/controls/universal/GroupBox.qml
@@ -53,8 +53,6 @@ T.GroupBox {
     padding: 12
     topPadding: padding + (label && label.implicitWidth > 0 ? label.implicitHeight + spacing : 0)
 
-    contentItem: Item { }
-
     label: Text {
         x: control.leftPadding
         width: control.availableWidth
diff --git a/src/imports/controls/universal/Page.qml b/src/imports/controls/universal/Page.qml
index eca623f1..4f2d6ff7 100644
--- a/src/imports/controls/universal/Page.qml
+++ b/src/imports/controls/universal/Page.qml
@@ -41,8 +41,6 @@ import QtQuick.Controls.Universal 2.1
 T.Page {
     id: control
 
-    contentItem: Item { }
-
     background: Rectangle {
         color: control.Universal.background
     }
diff --git a/src/imports/controls/universal/Pane.qml b/src/imports/controls/universal/Pane.qml
index 183f278c..2a459630 100644
--- a/src/imports/controls/universal/Pane.qml
+++ b/src/imports/controls/universal/Pane.qml
@@ -49,8 +49,6 @@ T.Pane {
 
     padding: 12
 
-    contentItem: Item { }
-
     background: Rectangle {
         color: control.Universal.background
     }
diff --git a/src/imports/controls/universal/Popup.qml b/src/imports/controls/universal/Popup.qml
index 36e87449..67dfa45c 100644
--- a/src/imports/controls/universal/Popup.qml
+++ b/src/imports/controls/universal/Popup.qml
@@ -51,8 +51,6 @@ T.Popup {
 
     padding: 12
 
-    contentItem: Item { }
-
     background: Rectangle {
         color: control.Universal.chromeMediumLowColor
         border.color: control.Universal.chromeHighColor
diff --git a/src/imports/controls/universal/ToolBar.qml b/src/imports/controls/universal/ToolBar.qml
index 49889e19..5535a337 100644
--- a/src/imports/controls/universal/ToolBar.qml
+++ b/src/imports/controls/universal/ToolBar.qml
@@ -47,8 +47,6 @@ T.ToolBar {
     contentWidth: contentItem.implicitWidth || (contentChildren.length === 1 ? contentChildren[0].implicitWidth : 0)
     contentHeight: contentItem.implicitHeight || (contentChildren.length === 1 ? contentChildren[0].implicitHeight : 0)
 
-    contentItem: Item { }
-
     background: Rectangle {
         implicitHeight: 48 // AppBarThemeCompactHeight
         color: control.Universal.chromeMediumColor
diff --git a/src/quicktemplates2/qquickcontrol.cpp b/src/quicktemplates2/qquickcontrol.cpp
index 518255dd..6e35e64e 100644
--- a/src/quicktemplates2/qquickcontrol.cpp
+++ b/src/quicktemplates2/qquickcontrol.cpp
@@ -214,6 +214,11 @@ void QQuickControlPrivate::resizeContent()
     }
 }
 
+QQuickItem *QQuickControlPrivate::getContentItem()
+{
+    return contentItem;
+}
+
 #ifndef QT_NO_ACCESSIBILITY
 void QQuickControlPrivate::accessibilityActiveChanged(bool active)
 {
@@ -1082,8 +1087,8 @@ void QQuickControl::setBackground(QQuickItem *background)
 */
 QQuickItem *QQuickControl::contentItem() const
 {
-    Q_D(const QQuickControl);
-    return d->contentItem;
+    QQuickControlPrivate *d = const_cast<QQuickControlPrivate *>(d_func());
+    return d->getContentItem();
 }
 
 void QQuickControl::setContentItem(QQuickItem *item)
diff --git a/src/quicktemplates2/qquickcontrol_p_p.h b/src/quicktemplates2/qquickcontrol_p_p.h
index 64f29986..26760510 100644
--- a/src/quicktemplates2/qquickcontrol_p_p.h
+++ b/src/quicktemplates2/qquickcontrol_p_p.h
@@ -88,6 +88,8 @@ public:
     void resizeBackground();
     virtual void resizeContent();
 
+    virtual QQuickItem *getContentItem();
+
 #ifndef QT_NO_ACCESSIBILITY
     void accessibilityActiveChanged(bool active) override;
     QAccessible::Role accessibleRole() const override;
diff --git a/src/quicktemplates2/qquickpage.cpp b/src/quicktemplates2/qquickpage.cpp
index 54e79fbe..88eb03bf 100644
--- a/src/quicktemplates2/qquickpage.cpp
+++ b/src/quicktemplates2/qquickpage.cpp
@@ -87,10 +87,20 @@ class QQuickPagePrivate : public QQuickControlPrivate
     Q_DECLARE_PUBLIC(QQuickPage)
 
 public:
+    QQuickItem *getContentItem() override;
+
     QString title;
     QScopedPointer<QQuickPageLayout> layout;
 };
 
+QQuickItem *QQuickPagePrivate::getContentItem()
+{
+    Q_Q(QQuickPage);
+    if (!contentItem)
+        contentItem = new QQuickItem(q);
+    return contentItem;
+}
+
 QQuickPage::QQuickPage(QQuickItem *parent) :
     QQuickControl(*(new QQuickPagePrivate), parent)
 {
@@ -225,7 +235,7 @@ void QQuickPage::setFooter(QQuickItem *footer)
 QQmlListProperty<QObject> QQuickPage::contentData()
 {
     Q_D(QQuickPage);
-    return QQmlListProperty<QObject>(d->contentItem, nullptr,
+    return QQmlListProperty<QObject>(d->getContentItem(), nullptr,
                                      QQuickItemPrivate::data_append,
                                      QQuickItemPrivate::data_count,
                                      QQuickItemPrivate::data_at,
@@ -248,7 +258,7 @@ QQmlListProperty<QObject> QQuickPage::contentData()
 QQmlListProperty<QQuickItem> QQuickPage::contentChildren()
 {
     Q_D(QQuickPage);
-    return QQmlListProperty<QQuickItem>(d->contentItem, nullptr,
+    return QQmlListProperty<QQuickItem>(d->getContentItem(), nullptr,
                                         QQuickItemPrivate::children_append,
                                         QQuickItemPrivate::children_count,
                                         QQuickItemPrivate::children_at,
diff --git a/src/quicktemplates2/qquickpane.cpp b/src/quicktemplates2/qquickpane.cpp
index 9f9c139b..ea296eb6 100644
--- a/src/quicktemplates2/qquickpane.cpp
+++ b/src/quicktemplates2/qquickpane.cpp
@@ -108,6 +108,14 @@ QQuickPanePrivate::QQuickPanePrivate() : contentWidth(0), contentHeight(0)
 {
 }
 
+QQuickItem *QQuickPanePrivate::getContentItem()
+{
+    Q_Q(QQuickPane);
+    if (!contentItem)
+        contentItem = new QQuickItem(q);
+    return contentItem;
+}
+
 QQuickPane::QQuickPane(QQuickItem *parent) :
     QQuickControl(*(new QQuickPanePrivate), parent)
 {
@@ -191,7 +199,7 @@ void QQuickPane::setContentHeight(qreal height)
 QQmlListProperty<QObject> QQuickPane::contentData()
 {
     Q_D(QQuickPane);
-    return QQmlListProperty<QObject>(d->contentItem, nullptr,
+    return QQmlListProperty<QObject>(d->getContentItem(), nullptr,
                                      QQuickItemPrivate::data_append,
                                      QQuickItemPrivate::data_count,
                                      QQuickItemPrivate::data_at,
@@ -214,7 +222,7 @@ QQmlListProperty<QObject> QQuickPane::contentData()
 QQmlListProperty<QQuickItem> QQuickPane::contentChildren()
 {
     Q_D(QQuickPane);
-    return QQmlListProperty<QQuickItem>(d->contentItem, nullptr,
+    return QQmlListProperty<QQuickItem>(d->getContentItem(), nullptr,
                                         QQuickItemPrivate::children_append,
                                         QQuickItemPrivate::children_count,
                                         QQuickItemPrivate::children_at,
diff --git a/src/quicktemplates2/qquickpane_p_p.h b/src/quicktemplates2/qquickpane_p_p.h
index acc0d0ab..62789664 100644
--- a/src/quicktemplates2/qquickpane_p_p.h
+++ b/src/quicktemplates2/qquickpane_p_p.h
@@ -61,6 +61,8 @@ class Q_QUICKTEMPLATES2_PRIVATE_EXPORT QQuickPanePrivate : public QQuickControlP
 public:
     QQuickPanePrivate();
 
+    QQuickItem *getContentItem() override;
+
     qreal contentWidth;
     qreal contentHeight;
 };
diff --git a/src/quicktemplates2/qquickpopup.cpp b/src/quicktemplates2/qquickpopup.cpp
index d2625c3e..a8e07533 100644
--- a/src/quicktemplates2/qquickpopup.cpp
+++ b/src/quicktemplates2/qquickpopup.cpp
@@ -352,6 +352,8 @@ public:
 
     void resolveFont() override;
 
+    QQuickItem *getContentItem() override;
+
     QQuickPopup *popup;
 };
 
@@ -378,6 +380,14 @@ void QQuickPopupItemPrivate::resolveFont()
         inheritFont(window->font());
 }
 
+QQuickItem *QQuickPopupItemPrivate::getContentItem()
+{
+    Q_Q(QQuickPopupItem);
+    if (!contentItem)
+        contentItem = new QQuickItem(q);
+    return contentItem;
+}
+
 QQuickPopupItem::QQuickPopupItem(QQuickPopup *popup) :
     QQuickControl(*(new QQuickPopupItemPrivate(popup)), nullptr)
 {