void MyFrame::CreateControls()
{


    //Adding menu and menu items . To add menu items add your code here.


    wxBoxSizer *mainsizer = new wxBoxSizer( wxVERTICAL);
    wxBoxSizer *button_sizer = new wxBoxSizer( wxHORIZONTAL );
    button_sizer->Add(
        new wxButton( this, wxID_LOAD, "Load" ),
        0,           // make horizontally unstretchable
        wxALL,       // make border all around (implicit top alignment)
        10 );        // set border width to 10
    button_sizer->Add(
        new wxButton( this, wxID_CANCEL, "Cancel" ),
        0,           // make horizontally unstretchable
        wxALL,       // make border all around (implicit top alignment)
        10 );        // set border width to 10

    wxBoxSizer *tree_sizer = new wxBoxSizer( wxHORIZONTAL );


    tree = new MyTreeCtrl(this, wxID_TREE,
        wxDefaultPosition, wxSize(250,300),
        wxTR_DEFAULT_STYLE);
    tree->mypanel = new MyPanel(this,wxID_PANEL,wxDefaultPosition,wxSize(250,250),wxTAB_TRAVERSAL|wxBORDER_SUNKEN);


    tree_sizer->Add(tree,1,wxEXPAND |    // make horizontally stretchable
        wxALL|wxALIGN_LEFT,        //   and make border all around
        10);
    tree_sizer->Add(tree->mypanel,1,wxEXPAND |    // make horizontally stretchable
        wxALL|wxALIGN_LEFT,        //   and make border all around
        10);

    mainsizer->Add(tree_sizer,1,            // make vertically stretchable
        wxEXPAND |    // make horizontally stretchable
        wxALL|wxALIGN_CENTRE,        //   and make border all around
        10);
    mainsizer->Add(
        button_sizer,
        0,                // make vertically unstretchable
        wxALIGN_CENTRE ); // no border and allign right

    SetSizer(mainsizer );      // use the sizer for layout
    this->Refresh(true);
    this->Show(true);
};



void MyTreeCtrl::OnSelChanged(wxTreeEvent& event)
{
    wxTreeItemId itemId = event.GetItem();
    this->SetEventItemId(itemId);
    wxString name=this->GetItemText(itemId);
    wxTreeItemData *data=new MyData();
    MyData* tData;
    data=this->GetItemData(itemId);
    tData = dynamic_cast<MyData*>(data);
    wxTreeItemId rootid = this->GetRootItem();
    if (itemId == rootid)
    {
        this->PopulateTextNode();
    }
    else if (tData->type == wxXML_ELEMENT_NODE)
    {
        this->PopulateElementNode(itemId);
    }
    else
        this->PopulateTextNode();

}



   1.
      void MyTreeCtrl::PopulateElementNode(wxTreeItemId &id)
   2.
      {
   3.

   4.
      //adding panel control elements and setting its sizer
   5.

   6.
         //the next two lines do not work .  A MyTreeCtrl  and a MyPanel are children of MyFrame ,which is the top level window. A MyPanel object exists inside MyTreeCtrl Class.An event on a node in the tree should populate the panel.I am setting a sizer with the panel ,but it does not get set. The sizer for the toplevel frame was set at a different place before this event.
   7.

   8.
              wxBoxSizer *paneltopsizer = new wxBoxSizer(wxVERTICAL);
   9.
              (this->mypanel)->SetSizer(paneltopsizer);
  10.

  11.

  12.
              this->MyListCtrl=new wxListCtrl(this->mypanel,
  13.
                      wxID_LISTCTRL,wxDefaultPosition,wxSize(245,100),wxLC_REPORT);
  14.
              wxButton *Add=new wxButton(this->mypanel,wxID_ADD,wxT("Add"));
  15.
              *Delete=new wxButton(this->mypanel,wxID_DELETE,wxT("Delete"));
  16.
              wxButton *ApplyChanges=new wxButton(this->mypanel,wxID_APPLYCHANGES,wxT("ApplyChanges"));
  17.

  18.
              wxBoxSizer *panelbuttonsizer = new wxBoxSizer(wxHORIZONTAL);
  19.
              panelbuttonsizer->Add(Add,0,wxALL|wxALIGN_RIGHT,5);
  20.
              panelbuttonsizer->Add(Delete,0,wxALL|wxALIGN_RIGHT,5);
  21.
              panelbuttonsizer->Add(ApplyChanges,0,wxALL|wxALIGN_RIGHT,5);
  22.
              paneltopsizer->Add(this->MyListCtrl,1,wxALL|wxEXPAND,10);
  23.
              paneltopsizer->Add(panelbuttonsizer,0, wxALIGN_CENTER_HORIZONTAL|wxALL, 5);
  24.

  25.
      //panel control ends
  26.
      }