如何清空一个只读文本框的内容,类似msn或者popo的聊天窗口

                            
用了n多api函数都不行,哪位高手看看?   
      SendMessage(hMsgWnd,EM_SETREADONLY,0,0);  
      SendMessage(hMsgWnd,EM_SETMODIFY,1,0);  
      SendMessage(hMsgWnd,EM_SETLIMITTEXT,100,0);  
   
   
      sendmessage(hMsgWnd,WM_SETTEXT,0,integer(pchar(sSend)));  
      SendMessage(hMsgWnd,WM_SETREDRAW,1,0);  
      SendMessage(hMsgWnd,EM_SETSEL,0,-1);  
      SendMessage(hMsgWnd,EM_REPLACESEL,1,integer(@sSend));

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