Declare Function FindWindowEx Lib "user32" Alias "FindWindowExA" (ByVal hWnd1 As Long, ByVal hWnd2 As Long, ByVal lpsz1 As String, ByVal lpsz2 As String) As Long
Declare Function PostMessage Lib "user32" Alias "PostMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
Declare Function MapVirtualKey Lib "user32" Alias "MapVirtualKeyA" (ByVal wCode As Long, ByVal wMapType As Long) As Long

Public Const WM_KEYDOWN = &H100
Public Const WM_KEYUP = &H101
Public Const WM_CHAR = &H102

'虚拟码转为扫描码
Function MakeKeyLparam(ByVal VirtualKey As Long, ByVal flag As Long) As Long
      Dim s As String
      Dim Firstbyte As String           'lparam参数的24-31位
      If flag = WM_KEYDOWN Then             '如果是按下键
              Firstbyte = "00"
      Else
              Firstbyte = "C0"                   '如果是释放键
      End If
      Dim Scancode As Long
      '获得键的扫描码
      Scancode = MapVirtualKey(VirtualKey, 0)
      Dim Secondbyte As String         'lparam参数的16-23位，即虚拟键扫描码
      Secondbyte = Right("00" & Hex(Scancode), 2)
      s = Firstbyte & Secondbyte & "0001"                 '0001为lparam参数的0-15位，即发送次数和其它扩展信息
      MakeKeyLparam = Val("&H" & s)
End Function

Private Sub Form_Load()
    Dim notepad, edit As Long
    
    notepad = FindWindowEx(0, 0, "Notepad", vbNullString) '获取记事本句柄
    
    Do While (notepad > 0)
        edit = FindWindowEx(notepad, 0, "Edit", vbNullString) '获取记事本的输入框句柄
        
        PostMessage edit, WM_CHAR, Asc("m"), MakeKeyLparam(Asc("m"), WM_KEYDOWN) '输入m
        PostMessage edit, WM_CHAR, Asc("z"), MakeKeyLparam(Asc("z"), WM_KEYDOWN) '输入z
        PostMessage edit, WM_CHAR, Asc("w"), MakeKeyLparam(Asc("w"), WM_KEYDOWN) '输入w
        PostMessage edit, WM_CHAR, Asc("u"), MakeKeyLparam(Asc("u"), WM_KEYDOWN) '输入u
        PostMessage edit, WM_CHAR, Asc("."), MakeKeyLparam(Asc("."), WM_KEYDOWN) '输入.
        PostMessage edit, WM_CHAR, Asc("c"), MakeKeyLparam(Asc("c"), WM_KEYDOWN) '输入c
        PostMessage edit, WM_CHAR, Asc("o"), MakeKeyLparam(Asc("o"), WM_KEYDOWN) '输入o
        PostMessage edit, WM_CHAR, Asc("m"), MakeKeyLparam(Asc("m"), WM_KEYDOWN) '输入m
        
        notepad = FindWindowEx(0, notepad, "Notepad", vbNullString) '获取下一个记事本句柄
    Loop
End Sub