button not work when i used wx.SplittedWindow

I create two windows in the frame by using wx.SplitterWindow, when I create a close button, this button does not ever work. Though I write code commonly in use.

ttp = wx.Button(panelOne, -1, 'Cancel', size=(90, 28), pos=(120, 280))
self.Bind(wx.EVT_BUTTON, self.OnClose, ttp)

 def OnClose(self, event):
    self.Close(True)

The full code I created

#!python
# -*- coding: utf-8 -*-


import sys
import wx

class MainFrame(wx.Frame):
    """"""

    #----------------------------------------------------------------------
    def __init__(self):
        """Constructor"""
        wx.Frame.__init__(self, None, title="Nested Splitters",
                          size=(1000,400))
        panel = MainPanel(self)
        self.Show()

class RandomPanel(wx.Panel):
    """"""

    #----------------------------------------------------------------------
    def __init__(self, parent, color):
        """Constructor"""
        wx.Panel.__init__(self, parent)
        self.SetBackgroundColour(color)

class MainPanel(wx.Panel):
    """"""

    #----------------------------------------------------------------------
    def __init__(self, parent):
        """Constructor"""
        wx.Panel.__init__(self, parent)

        topSplitter = wx.SplitterWindow(self)
        vSplitter = wx.SplitterWindow(topSplitter) 

        panelOne = RandomPanel(topSplitter, "grey")
        text1 = wx.StaticText(panelOne, -1, 'You', pos=(10, 4))
        self.txt = wx.TextCtrl(panelOne, -1, size=(200, 20), pos=(10, 20))
        text2 = wx.StaticText(panelOne, -1, 'Scarlett', pos=(10, 45))
        self.klm = wx.TextCtrl(panelOne, -1, size=(200, 200), pos=(10, 65))

        panelTwo = RandomPanel(topSplitter, "red")
        self.txt = wx.TextCtrl(panelTwo, -1, size=(200, 100))
        topSplitter.SplitVertically(panelOne, panelTwo)
        topSplitter.SetSashGravity(0.5)

        entr = wx.Button(panelOne, -1, 'Ok', size=(90, 28), pos=(10, 280))
        ttp = wx.Button(panelOne, -1, 'Cancel', size=(90, 28), pos=(120, 280))

        self.Bind(wx.EVT_BUTTON, self.OnClose, ttp)
        #self.Bind(wx.EVT_BUTTON, self.OnEnter, entr)

        #panelThree = RandomPanel(topSplitter, "green")
        #topSplitter.SplitVertically(vSplitter, panelThree)
        #topSplitter.SetSashGravity(0.5)

        sizer = wx.BoxSizer(wx.VERTICAL)
        sizer.Add(topSplitter, 1, wx.EXPAND)
        self.SetSizer(sizer)

        self.Center()
        self.Show(True)

    def OnClose(self, event):
        self.Close(True)

#    def OnEnter(self, event):
#       self.result.SetLabel(self.PatMatch())

#----------------------------------------------------------------------

    if __name__ == "__main__":
     app = wx.App(False)
     frame = MainFrame()
     app.MainLoop()