下載文件

Question

目前我使用這個代碼，以獲取文件：

WebClient webClient = new WebClient(); 
webClient.DownloadProgressChanged += webClient_DownloadProgressChanged; 
webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(webClient_ProgressCompleted); 

我爲了弄清楚如何把這個一直走在文檔看看使用Rx編碼。

我已經開始使用FromEvent創建Observable以注意DownloadFileCompleted事件。

Observable.FromEvent<?>(?, ?) 

不過，我無法計算如何填寫這些?。

有人能給我一個例子嗎？

到現在爲止，我已經試過：

Observable.FromEvent<AsyncCompletedEventArgs>(?1:addHandler, ?2:removeHandler). 

儘管如此，.NET是請求我?1:addHandler和?2:removeHandler是Action<Action<AsyncCompletedEventArgs>>（那是什麼）？

Answer 1

這些重載是如此棘手，我必須look them up every time。我已經包括了一些樣本，申購代碼，讓你開始：

WebClient webClient = new WebClient(); 
var progressChangedObservable = Observable.FromEventPattern<DownloadProgressChangedEventHandler, DownloadProgressChangedEventArgs>(
    h => webClient.DownloadProgressChanged += h, 
    h => webClient.DownloadProgressChanged -= h 
); 

var downloadCompletedObservable = Observable.FromEventPattern<AsyncCompletedEventHandler, AsyncCompletedEventArgs>(
    h => webClient.DownloadFileCompleted += h, 
    h => webClient.DownloadFileCompleted -= h 
); 

progressChangedObservable 
    .Select(ep => ep.EventArgs) 
    .Subscribe(dpcea => Console.WriteLine($"{dpcea.ProgressPercentage}% complete. {dpcea.BytesReceived} bytes received. {dpcea.TotalBytesToReceive} bytes to receive.")); 

downloadCompletedObservable 
    .Select(ep => ep.EventArgs) 
    .Subscribe(_ => Console.WriteLine("Download file complete.")); 

var dummyDownloadPath = @"C:\temp\temp.txt"; 
webClient.DownloadFileAsync(new Uri(@"http://google.com"), dummyDownloadPath); 

---

編輯：

每@ Enigmativity的建議，這是可以做到所有這些代碼在功能風格，也處理清理所有IDisposable s。但是，我不覺得它是可讀的，因此不會推薦它：

Observable.Using(() => 
    { 
     var webClient = new WebClient(); 
     webClient.Headers.Add("User-Agent: Other"); 
     return webClient; 
    }, webClient => 
    Observable.Using(() => 
     Observable.FromEventPattern<DownloadProgressChangedEventHandler, DownloadProgressChangedEventArgs>(
       h => webClient.DownloadProgressChanged += h, 
       h => webClient.DownloadProgressChanged -= h 
      ) 
      .Select(ep => ep.EventArgs) 
      .Subscribe(dpcea => Console.WriteLine($"{dpcea.ProgressPercentage}% complete. {dpcea.BytesReceived} bytes received. {dpcea.TotalBytesToReceive} bytes to receive.")), 
     sub1 => Observable.Using(() => 
      Observable.FromEventPattern<AsyncCompletedEventHandler, AsyncCompletedEventArgs>(
        h => webClient.DownloadFileCompleted += h, 
        h => webClient.DownloadFileCompleted -= h 
       ) 
       .Select(ep => ep.EventArgs) 
       .Subscribe(_ => Console.WriteLine("Download file complete.")), 
      sub2 => webClient.DownloadFileTaskAsync(new Uri(@"http://google.com"), @"C:\temp\temp.txt").ToObservable() 
     ) 
    ) 
) 
    .Subscribe(_ => {}); //Subscription required to trigger nested observables