Designer: Extend container extension.

Make it possible to disable adding/removing pages by
adding respective bool virtual functions.

Useful for implementing containers with fixed, single
children like QScrollArea, QDockWidget, which require
a container extension to work properly in Qt Designer.
Previously, the problem was that the add/remove
page context menu actions were enabled for them,
leading to crashes und undesired behaviour.

Reviewed-by: Jarek Kobus <jaroslaw.kobus@nokia.com>

tools/uilib/container.h

@@ -65,6 +65,13 @@ public:
     virtual void addWidget(QWidget *widget) = 0;
     virtual void insertWidget(int index, QWidget *widget) = 0;
     virtual void remove(int index) = 0;
+
+    virtual bool canAddWidget() const
+    // ### Qt6 remove body, provided in Qt5 for source compatibility to Qt4.
+         { return true; }
+    virtual bool canRemove(int index) const
+    // ### Qt6 remove body, provided in Qt5 for source compatibility to Qt4.
+         { Q_UNUSED(index); return true; }
 };
 Q_DECLARE_EXTENSION_INTERFACE(QDesignerContainerExtension, "com.trolltech.Qt.Designer.Container")
 

tools/uilib/container.qdoc

@@ -170,3 +170,30 @@
 
     \sa addWidget(), insertWidget()
 */
+
+/*!
+    \fn bool QDesignerContainerExtension::canAddWidget() const
+
+    Returns whether a widget can be added. This determines whether
+    the context menu options to add or insert pages are enabled.
+
+    This should return false for containers that have a single, fixed
+    page, for example QScrollArea or QDockWidget.
+
+    \since 5.0
+    \sa addWidget(), canRemove()
+*/
+
+/*!
+    \fn bool QDesignerContainerExtension::canRemove(int index) const
+
+    Returns whether the widget at the given \a index can be removed.
+    This determines whether the context menu option to remove the current
+    page is enabled.
+
+    This should return false for containers that have a single, fixed
+    page, for example QScrollArea or QDockWidget.
+
+    \since 5.0
+    \sa remove(), canAddWidget()
+*/