本例是Form中有一个按钮。

点击按钮，Form的Title会显示指定的文字。

Public Class Form3

Private Declare Auto Function SendMessage Lib "user32" Alias "SendMessageW" (ByVal hwnd As Integer,ByVal wMsg As Integer,ByVal wParam As Integer,ByVal lParam As String) As Integer

Private Const EM_SETTEXT = &HC ' VB中&H表示16进制
'Private Const WM_GETTEXT = &HC

Private Sub Button1_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles Button1.Click

Dim hwnd As IntPtr = CType(Me.Handle,IntPtr)

'Sendmessage(目标控件句柄,自定义消息类型,参数个数,消息内容)
SendMessage(hwnd,EM_SETTEXT,"myTest")

End Sub

End Class