UIAlertView(警告)的创建

  initWithTitle:message:delegate:cancelButtonTitle:otherButtonTitles:
   注释：initWithTitle是对象函数
               initWithTitle:警告框标题
               message:警告内容
               delegate:接收对象
               cancelButtonTitle:关闭按钮标题
               otherButtonTitles:其他按钮