Allow marking wxTreeBook nodes to expand initially in XRC.

Add new "expanded" attribute for XRC nodes of treebookpage class.

Also update the sample and the XRC format documentation.

Closes #13355.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68318 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/xrc/xh_treebk.cpp

@@ -76,6 +76,24 @@ wxObject *wxTreebookXmlHandler::DoCreateResource()
 
         CreateChildren(m_tbk, true/*only this handler*/);
 
+        wxXmlNode *node = GetParamNode("object");
+        int pageIndex = 0;
+        for (unsigned int i = 0; i < m_tbk->GetPageCount(); i++)
+        {
+            if ( m_tbk->GetPage(i) )
+            {
+                wxXmlNode *child = node->GetChildren();
+                while (child)
+                {
+                    if (child->GetName() == "expanded" && child->GetNodeContent() == "1")
+                        m_tbk->ExpandNode(pageIndex, true);
+
+                    child = child->GetNext();
+                }
+                pageIndex++;
+            }
+        }
+
         m_treeContext = old_treeContext;
         m_isInside = old_ins;
         m_tbk = old_par;