private delegate void SetTextBoxValueDelegate(string value);
private void SetTextBoxValue(string value)
{
    if (this.txtInfo.InvokeRequired)//判斷是否跨線程請求
    {
        SetTextBoxValueDelegate myDelegate = delegate(string text) { txtInfo.Text = text; };
        txtInfo.Invoke(myDelegate, value);
    }
    else
    {
        txtInfo.Text = value;
    }
}

private void SetTextBoxValue(string value)
{
    Action<string> setValueAction = text => txtInfo.Text = text;//Action<T>本身就是delegate類型，省掉了delegate的定義
    if (this.txtInfo.InvokeRequired)
    {
        txtInfo.Invoke(setValueAction, value);
    }
    else
    {
        setValueAction(value);
    }
}