VB.net中通过窗口名称取得后台窗口句柄

Public Class Form1
    Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Integer
    Private Declare Function FindWindowEx Lib "user32" Alias "FindWindowExA" (ByVal hWnd1 As Long, ByVal hWnd2 As Long, ByVal lpsz1 As String, ByVal lpsz2 As String) As Integer
    Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Int32, ByVal wMsg As Int32, ByVal wParam As Int32, ByVal lParam As Int32) As Int32

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim myhwnd As Integer
        Dim subHwnd As Integer
        myhwnd = FindWindow("Notepad", "test.txt - メモ��")
        subHwnd = FindWindowEx(myhwnd, 0, "Edit", 0)
        SendMessage(subHwnd, &H302, 0, 0)
        'MsgBox(subHwnd)
    End Sub
End Class
myhwnd = FindWindow("Notepad", "test.txt - メモ��")