C#SendKeys的用法

this.richTextBox1.Focus(); 
        for(int i=65;i<91;i++)
        {            
            char Letter=(char)i; 
            SendKeys.Send(Letter.ToString());
            System.Threading.Thread.Sleep(100); 
            SendKeys.Flush();
        }             
        for(int i=97;i<123;i++)
        {           
            char Letter=(char)i;
            SendKeys.Send(Letter.ToString());
            System.Threading.Thread.Sleep(100);
            SendKeys.Flush(); 
        }