其中SendAsync方法時的HttpClientHandler傳遞給HttpClient的被稱爲

大多數自定義請求屬性的HttpClientHandler定義，這個類是HttpMessageHandler一個子類，類定義是這樣的：其中SendAsync方法時的HttpClientHandler傳遞給HttpClient的被稱爲

public abstract class HttpMessageHandler : IDisposable 
{ 
    protected internal abstract Task<HttpResponseMessage> SendAsync 
    (HttpRequestMessage request, CancellationToken cancellationToken); 
    public void Dispose(); 
    protected virtual void Dispose (bool disposing); 
}

書<C#5.0 in a nutshell>表示在調用HttpClient的SendAsync方法時調用中的SendAsync方法。但是HttpClient類也定義了一個SendAsync方法，當我們調用HttpClient的實例時，調用SendAsync這個方法？

來源

2013-01-07 Allen4Tech

總結你的問題：HttpClient的有一個方法SendAsync。 HttpMessageHandler有一個方法SendAsync（由HttpClientHandler覆蓋）。 HttpClient.SendAsync調用HttpMessageHandler.SendAync。有什麼問題？ – dtb

你的意思是HttpClient.SendAsync調用HttpMessageHandler的SendAsync方法，而不是它自己的？ – Allen4Tech

當您調用HttpClient.SendAsync時，則執行HttpClient.SendAsync。當執行HttpClient.SendAsync時，它會調用HttpMessageHandler.SendAsync。 – dtb

這是發生了什麼本質：

HttpMessageInvoker &的HttpClient

class HttpMessageInvoker 
{ 
    private HttpMessageHandler handler; 

    public HttpMessageInvoker(HttpMessageHandler handler) 
    { 
     this.handler = handler; 
    } 

    public virtual void SendAsync() 
    { 
     Console.WriteLine("HttpMessageInvoker.SendAsync"); 
     this.handler.SendAsync(); 
    } 
} 

class HttpClient : HttpMessageInvoker 
{ 
    public HttpClient(HttpMessageHandler handler) 
     : base(handler) 
    { 
    } 

    public override void SendAsync() 
    { 
     Console.WriteLine("HttpClient.SendAsync"); 
     base.SendAsync(); 
    } 
}

HttpMessageHandler & HttpClientHandler

abstract class HttpMessageHandler 
{ 
    protected internal abstract void SendAync(); 
} 

class HttpClientHandler : HttpMessageHandler 
{ 
    protected internal override void SendAync() 
    { 
     Console.WriteLine("HttpClientHandler.SendAsync"); 
    } 
}

所以，如果你SendAsync在HttpClient實例上，該方法被執行。該方法從HttpMessageInvoker調用SendAsync方法。該方法調用HttpMessageHandler實例的SendAsync方法。 HttpMessageHandler是抽象的; HttpClientHandler通過覆蓋它來提供抽象SendAync方法的具體實現。

例子：

var handler = new HttpClientHandler(); 
var client = new HttpClient(handler); 
client.SendAsync();

輸出：

 
HttpClient.SendAsync 
HttpMessageInvoker.SendAsync 
HttpClientHandler.SendAsync

來源

2013-01-07 08:53:13 dtb

其中SendAsync方法時的HttpClientHandler傳遞給HttpClient的被稱爲

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