异步委托

private delegate double RunAsyncEventHandler(double douA, double douB);
private delegate void SetSendTextEventHandler(string strText);
private RunAsyncEventHandler asyncHandler;

private void btnSend_Click(object sender, EventArgs e)
{
    asyncHandler = new RunAsyncEventHandler(RunAsync);
    asyncHandler.BeginInvoke(5d, 3d, new AsyncCallback(GetAsyncResult), null);
}

public double RunAsync(double douA, double douB)
{
    Thread.Sleep(3000);
    return douA + douB;
}

public void GetAsyncResult(IAsyncResult result)
{
    double douResult = asyncHandler.EndInvoke(result);

    //1.第一种方法
    this.Invoke(new SetSendTextEventHandler(rtbSend.AppendText), 
        new object[] { douResult.ToString() + "\n" });

    //2.第二种方法
    SetSendText(douResult.ToString());
}

public void SetSendText(string strText)
{
    if (this.InvokeRequired)
    {
        SetSendTextEventHandler handler = 
            new SetSendTextEventHandler(SetSendText);
        this.Invoke(handler, new object[] { strText });
    }
    else
    {
        lock (rtbSend)
        {
            rtbSend.AppendText(strText);
            rtbSend.AppendText("\n");
        }
    }
}