主题：求注，遍历所有窗口中的所有控件

  For Each c As WinForm.Control In frm.Controls
        If Typeof c Is WinForm.PictureBox Then '判断控件是否是文本框
            Dim t As WinForm.PictureBox = c '使用特定类型的变量引用控件
            t.remote = True
            t.FTPclient = ftp1
        End If
    Next