ui線程訪問時候 用invoke激發,字符串是拼接的末端加了\r\n  為什么不會換行? 
MethodInvoker 和action好像都可以實現,區別在哪,或者更好一點
strQR = string.Format("{0}:{1}", "二維碼", HandleCodeString(QRCodeArr));
   public void Show(string msg)
        {
            richTextBox1.Invoke(new MethodInvoker(delegate() {
                richTextBox1.AppendText(msg + "\r\n");
                if (richTextBox1.Lines.Length > 2000)
                {
                    richTextBox1.Clear();
                }
                richTextBox1.ScrollToCaret();
            }));           
        }