Problem setting value of wx.TextCtrl in wxPython

I'm trying to pass the directory the user chooses back to the wx.TextCtrl named ChooseRoot. This has not worked so far.

What am I doing wrong? I tried different things, but either it hangs or I get this error message.

Traceback (most recent call last):
File "F:\Indexinator3000_x64.pyw", line 78, in OnChooseRoot
self.ChooseRoot.SetValue("Hello")
AttributeError: 'MainPanel' object has no attribute 'ChooseRoot'

import wx 

ID_EXIT = 110

class MainPanel(wx.Panel):
    def __init__(self, parent, id):
        wx.Panel.__init__(self, parent, id)
        self.parent = parent

        #------------- Setting up the buttons
        self.Run = wx.Button(self, label="Run")
        self.Run.Bind(wx.EVT_BUTTON, self.OnRun )
        self.ExitB = wx.Button(self, label="Exit")
        self.ExitB.Bind(wx.EVT_BUTTON, self.OnExit)

        #------------- Setting up Static text
        self.labelChooseRoot = wx.StaticText(self, label ="Root catalog: ") 
        self.labelScratchWrk = wx.StaticText(self, label ="Sratch workspace: ")
        self.labelMergeFile = wx.StaticText(self, label ="Merge file: ")

        #------------ Setting up inputtext
        self.ChooseRoot = wx.TextCtrl(self, -1, size=(210,-1))
        self.ChooseRoot.Bind(wx.EVT_LEFT_UP, self.OnChooseRoot)
        self.ScratchWrk = wx.TextCtrl(self, -1, size=(210,-1))
        self.MergeFile = wx.TextCtrl(self, -1, size=(210,-1))


        #------------- Setting up the outputbox
        self.Output = wx.TextCtrl(self, style=wx.TE_MULTILINE|wx.TE_READONLY)

        #------------- Setting up the sizer
        SizerF = wx.FlexGridSizer(3,2,5,5)
        SizerF.Add(labelChooseRoot)      #row 1, col 1
        SizerF.Add(ChooseRoot)           #row 1, col 2
        SizerF.Add(labelScratchWrk)      #row 2, col 1
        SizerF.Add(ScratchWrk)           #row 2, col 2
        SizerF.Add(labelMergeFile)       #row 3, col 1
        SizerF.Add(MergeFile)            #row 3, col 2

        SizerB = wx.BoxSizer(wx.VERTICAL)
        SizerB.Add(Run, 1, wx.ALIGN_RIGHT|wx.ALL, 5)
        SizerB.Add(ExitB, 0, wx.ALIGN_RIGHT|wx.ALL, 5)

        Sizer1 = wx.BoxSizer()
        Sizer1.Add(SizerF, 0, wx.ALIGN_RIGHT | wx.EXPAND | wx.ALL, 10)
        Sizer1.Add(SizerB, 0, wx.ALIGN_RIGHT | wx.EXPAND | wx.ALL)

        Sizer2 = wx.BoxSizer()
        Sizer2.Add(Output, 1, wx.EXPAND | wx.ALL, 5)

        SizerFinal = wx.BoxSizer(wx.VERTICAL)
        SizerFinal.Add(Sizer1, 0, wx.ALIGN_RIGHT | wx.EXPAND | wx.ALL)
        SizerFinal.Add(Sizer2, 1, wx.ALIGN_RIGHT | wx.EXPAND | wx.ALL)


        self.SetSizerAndFit(SizerFinal)

    #--- START EVENT HANDLERS

    def OnChooseRoot(self, Event=None):
        # In this case we include a "New directory" button. 
        dlg = wx.DirDialog(self, "Choose a directory:",
                          style=wx.DD_DEFAULT_STYLE
                           #| wx.DD_DIR_MUST_EXIST
                           #| wx.DD_CHANGE_DIR
                           )

        # If the user selects OK, then we process the dialog's data.
        # This is done by getting the path data from the dialog - BEFORE
        # we destroy it. 
        if dlg.ShowModal() == wx.ID_OK:
            RootPath = dlg.GetPath()
            self.ChooseRoot.SetValue(RootPath)

        # Only destroy a dialog after you're done with it.
        dlg.Destroy()

    def OnRun(self, Event=None):
        #First check if any of the boxes is empty
        pass

    def OnExit(self, Event=None):
        self.GetParent().Close()


    #--- END EVENT HANDLERS

class MainWindow(wx.Frame):
    def __init__(self, parent, id, title):
        wx.Frame.__init__(self, parent, wx.ID_ANY, title, size = (430,330),
                          style = wx.DEFAULT_FRAME_STYLE | wx.NO_FULL_REPAINT_ON_RESIZE | wx.STAY_ON_TOP)
        self.CreateStatusBar() 
        #------------- Setting up the menu
        filemenu = wx.Menu()
        filemenu.Append(ID_EXIT, "E&xit", "Exit the program")
        #------------- Creating the menu
        menubar = wx.MenuBar()
        menubar.Append(filemenu, "&File")
        self.SetMenuBar(menubar)
        #---------- Setting menu event handlers
        wx.EVT_MENU(self, ID_EXIT, self.OnExit)                    
        #--- Add MainPanel
        self.Panel = MainPanel(self, -1)

        self.SetMaxSize(self.GetSize()) #Sets the Maximum size the window can have
        self.SetMinSize(self.GetSize()) #Sets the Minimum size the window can have
        #Centre on Screen
        self.CentreOnScreen()

        ###---- SHOW THE WINDOW
        self.Show(True)

    def OnExit(self,  event):
        self.Close(True) # Close the Frame
    #--- END EVENT HANDLERS ---------------------------------



if __name__=='__main__':

    try:
        app = wx.PySimpleApp()
        frame = MainWindow(None, -1, "IndexGenerator")
        app.MainLoop()
    finally:
        del app