将RichTextBox设置为自动换行或非自动换行

　　近日研究文本控件和字符串，研究得头混脑胀，问题真是太多了。
　　这只是其中的一个问题，答案来自问专家网站和csdn的technofantasy(www.applevb.com) ，解决如下：

public const wm_user = &h400
public const em_settargetdevice = (wm_user + 72)

public declare function getdc lib "user32" (byval hwnd as long) as long
public declare function sendmessage lib "user32" alias "sendmessagea" _
  (byval hwnd as long, _
   byval wmsg as long, _
   byval wparam as long, _
   lparam as any) as long


public sub autoswitchline(byref richtext as long, byval bswitch as boolean)
    if bswitch then
        '设置 richtextbox 自动换行
        call sendmessage(richtext.hwnd, em_settargetdevice, _
        getdc(richtext.hwnd), richtext.width / 15)
        if richtext.rightmargin = 0 then
            richtext.rightmargin = 1
        else
            richtext.rightmargin = 0
        end if
    else
        '设置 richtextbox 不自动换行
        call sendmessage(richtext.hwnd, em_settargetdevice, 0, 1)
    end if
end sub