回车事件

 private void tbMsg_KeyDown(object sender, KeyEventArgs e)
        {
            KeyEventArgs keyEventArgs = e as KeyEventArgs;
            if (null != keyEventArgs && keyEventArgs.Key == Key.Enter)
            {
                if (tbMsg.Text == "")
                {
                    lbMsg.Items.Add("我:" + "测试发送");
                }
                else
                {
                    lbMsg.Items.Add("我:" + tbMsg.Text);
                }
                tbMsg.Text = "";
            }
        }