Dragging a wxWindow around

#include "wx/wx.h"
 
 
class MovableButton : public wxButton
    {
        bool dragging;
        int x,y;
        wxPanel* parent;
        
    public:
        
        MovableButton(wxPanel* parent) : wxButton(parent, wxID_ANY, wxT("Drag me around"))
        {
            MovableButton::parent = parent;
            dragging = false;
        }
        
        void onMouseDown(wxMouseEvent& evt)
        {
            CaptureMouse();
            x = evt.GetX();
            y = evt.GetY();
            dragging=true;
            //evt.Veto();
        }
        void onMouseUp(wxMouseEvent& evt)
        {
            ReleaseMouse();
            dragging=false;
        }
        void onMove(wxMouseEvent& evt)
        {
            if(dragging)
            {
                wxPoint mouseOnScreen = wxGetMousePosition();
                int newx = mouseOnScreen.x - x;
                int newy = mouseOnScreen.y - y;
                this->Move( parent->ScreenToClient( wxPoint(newx, newy) ) );
            }
        }
        
        DECLARE_EVENT_TABLE()
    };
 
BEGIN_EVENT_TABLE(MovableButton,wxButton)
EVT_LEFT_DOWN(MovableButton::onMouseDown)
EVT_LEFT_UP(MovableButton::onMouseUp)
EVT_MOTION(MovableButton::onMove)
END_EVENT_TABLE()
 
class MyFrame : public wxFrame
    {
        wxPanel* mainPanel;
    public:
        MyFrame(wxWindow* ptr, int id, wxString name, wxPoint pos, wxSize size) : wxFrame(ptr,id,name,pos,size)
        {
            mainPanel = new wxPanel(this, wxID_ANY);
            MovableButton* btn = new MovableButton(mainPanel);
            
            Center();
            Show();
        }
    };
 
class MyApp: public wxApp
    {
        virtual bool OnInit();
    };
 
 
IMPLEMENT_APP(MyApp)
 
 
bool MyApp::OnInit()
{
    MyFrame* frame = new MyFrame(NULL, wxID_ANY,  wxT("Dragging a widget"), wxDefaultPosition, wxSize(640, 480));
    
    return true;
}