PushStreamContent Web API

Question

我想將我的數據從web API推送到客戶端，所以我在Web API中使用PushStreamContent。 我的數據都是學生存在數據庫中。

public HttpResponseMessage GetAll() 
    { 
     HttpResponseMessage response = new HttpResponseMessage(); 
     var students = _symboleService.GetAll(); 
     response.Content = new PushStreamContent((students, httpContent, context) => 
     { 
      OnStreamAvailable(students, httpContent, context); 
     }, "text/plain"); 
     return response; 

    } 

    private void OnStreamAvailable(Stream stream, HttpContent content,TransportContext context) 
    { 
     StreamWriter responseStreamWriter = new StreamWriter(stream); 
     clients.Add(responseStreamWriter); 
    } 

但錯誤顯示在該線上的「學生」：

response.Content = new PushStreamContent((students, httpContent, context) => 

本地或命名參數「學生」不能在此範圍 聲明，因爲這個名字是在使用包圍本地範圍以限定 本地或參數

更新我在這裏的要點是將數據推送到客戶端， 一些修改後，該我的代碼，但它示出了在線路錯誤時，需要用於非靜態字段

var students = _symboleService.GetAll(); 

的對象引用，方法或 財產 'SymbolesController._symboleService'

private static readonly Lazy<Timer> _timer = new Lazy<Timer>(() => new Timer(TimerCallback, null, 0, 1000)); 
    private static readonly ConcurrentDictionary<StreamWriter, StreamWriter> _outputs = new ConcurrentDictionary<StreamWriter, StreamWriter>(); 

    public HttpResponseMessage GetAll() 
    { 
     HttpResponseMessage response = new HttpResponseMessage(); 
     response.Content = new PushStreamContent((responseStream, httpContent, context) => 
     { 
      StreamWriter responseStreamWriter = new StreamWriter(responseStream); 

      _outputs.TryAdd(responseStreamWriter, responseStreamWriter); 

     }, "text/plain"); 

     Timer t = _timer.Value; 

     return response; 
    } 



    // Runs every second after the first request to this controller and 
    // writes to the response streams of all currently active requests 
    private static void TimerCallback(object state) 
    { 

     foreach (var kvp in _outputs.ToArray()) 
     { 
      StreamWriter responseStreamWriter = kvp.Value; 

      try 
      { 
       var students = _symboleService.GetAll(); 
       responseStreamWriter.Write(students); 
       responseStreamWriter.Flush(); 
      } 
      catch { } 
     } 
    } 

順便說一句，如果我在這裏改變studentsby DateTime.Now，它的工作原理：

responseStreamWriter.Write(students); to 
responseStreamWriter.Write(DateTime.Now); 

Answer 1

您需要重命名PushStreamContent構造函數中使用的students參數。

例如，來自：

response.Content = new PushStreamContent((students, httpContent, context) => 
{ 
    OnStreamAvailable(students, httpContent, context); 
}, "text/plain"); 

到：

response.Content = new PushStreamContent((stream, httpContent, context) => 
{ 
    OnStreamAvailable(stream, httpContent, context); 
}, "text/plain"); 

爲什麼你不能使用students是因爲它已經被聲明爲前行的變量的原因：

var students = _symboleService.GetAll(); 

Answer 2

這裏有幾個問題會阻礙你的進步。

首先，您的PushStreamContent構造函數中的Action不能重用變量名「students」。看起來你認爲你正在通過對Action的引用，但這不是這個工作方式。

你可以試試這個：

response.Content = new PushStreamContent(OnStreamAvailable, "text/plain"); 

但仍存在另一個問題。 PushStreamContent構造函數的操作中的流是一個輸出流。

public PushStreamContent(Action<Stream, HttpContent, TransportContext> onStreamAvailable); 

您會想要從您的OnStreamAvailable處理程序中寫入該流。

由於不清楚什麼是_symbolService.GetAll（）方法，我只能推測從方法中生成的Byte []應該寫入到您的操作本身的輸出流中。

假設您的學生數據不是真正的流或固有流式，這可能是對PushStreamContent類的濫用。