Question

我在下载系统上工作，一次下载最多4个文件，如果下载时出错，则重试最多5次。我希望它在完成下载后用变量调用不同的回调。

这就是我写的：

private void Download(string url, (something) callback)
{
    if (asyncworkers++ < Global.paralleldownloads -1) // async download
    {
        using (WebClient client = new WebClient())
        {
            client.Proxy = (Global.proxymode == 2 ? new WebProxy(dynamicproxy) : (Global.proxymode == 1 ? new WebProxy(Global.proxy) : null));
            System.Timers.Timer timer = new System.Timers.Timer(5000);
            timer.Enabled = true;
            client.DownloadStringCompleted += (sender, e) => 
            {
                asyncworkers--;
                if (timer.Enabled)
                {
                    timer.Stop();
                    if (e.Error == null && e.Result.Length > 0)
                    {
                        AppendTextBox("successful async\r\n");
                        errors = 0;
                        //call "callback" and its variables here
                    }else{
                        AppendTextBox("empty async\r\n");
                        if (errors++ > 3)
                        {
                            //stop trying
                        }else{
                            Download(url, callback);
                        }
                    }
                }
            };
            client.DownloadStringAsync(new Uri(url));
            timer.Elapsed += (sender, e) =>
            {
                AppendTextBox("timeout async\r\n");
                timer.Enabled = false;
                client.CancelAsync();
                Download(url, callback);
            };
        }
    }else{ // sync download to delay it
        var request = WebRequest.Create(url);
        request.Proxy = (Global.proxymode == 2 ? new WebProxy(dynamicproxy) : (Global.proxymode == 1 ? new WebProxy(Global.proxy) : null));
        request.Timeout = 5000;
        using (var response = request.GetResponse())
        {
            using (var stream = response.GetResponseStream())
            {
                using (var reader = new StreamReader(stream))
                {
                    string data = reader.ReadToEnd();
                    if (data.Length > 0)
                    {
                        AppendTextBox("successful sync\r\n");
                        asyncworkers--;
                        errors = 0;
                        //call "callback" and its variables here
                        return;
                    }
                }
            }
        }
        asyncworkers--;
        AppendTextBox("error sync\r\n");
        if (errors++ > 3)
        {
            //stop trying
        }else{
            Download(url, callback);
        }
    }
}

这就是我想用它的方式：

Download("http://.....", GetDataDone(var1, var2, var3, var4));

或

Download("http://.....", UpdateDone());

我希望我所描述的至少对你来说有点清楚。我怎么能按照我希望的方式工作呢？谢谢！

Answer 1

将callback声明为Action<T1,T2,T3,T4>，其中T1是var1的类型，T2是var2等等。调用这样的回调：

public void Download(string url, Action<T1,..> callback)
{
    //....
    callback(var1,var2,var3,var4);
    //...
}

将具有匹配签名按名称的函数作为回调传递或使用lambda来匹配签名：

public void OnDownload(T1 var1, T2 var2, T3 var3, T4 var4)
{
     // do stuff here
}

//later
Download("http...", OnDownload);

评论后更新

使用lambda表达式预先传递参数：

public void Download(string url, Action callback)
{
     //...
     callback();
     //..
}


 Download("http://..", () => OnDownload(42, "request", user, 0.5f));

通过1个变量/对象调用回调

1 个答案: