extend HttpClient

本文关键字：HttpClient extend | 更新日期: 2023-09-27 18:06:30

我试图创建一个类，扩展httpclient，但仍然是抽象的。

public abstract class Repository : HttpClient
{
    public override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        //retry logic here
        var response = await base.SendAsync(request, cancellationToken);
        while (!IsValid(response))
        {
            Attempts++;
            response = await Retry(request, cancellationToken);
        }
        Attempts = 0;
        return response;
    }
    public int Attempts { get; set; }
    public abstract bool IsValid(HttpResponseMessage response);
    public abstract Task<HttpResponseMessage> Retry(HttpRequestMessage request, CancellationToken cancellationToken);
    public abstract Type GetPageForUri(Uri uri);
    public abstract Task<object> GetItems(Uri uri);
}

但是当子类调用getStringAsync时，它不会调用Repository中的SendAsync 

public class EmailClient : Repository
{
    public override bool IsValid(HttpResponseMessage response)
    {
        return response.IsSuccessStatusCode;
    }
    public override Task<HttpResponseMessage> Retry(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        return base.SendAsync(request, cancellationToken);
    }
    public override Type GetPageForUri(Uri uri)
    {
        return typeof(EmailPage);
    }
    public override async Task<object> GetItems(Uri uri)
    {
        var emails = await GetStringAsync(uri);
        return emails;
    }
}

我哪里做错了?我应该做一个HttpClientHandler，并包括与HttpClient?我试着读了一些关于虚拟的东西，如果有什么不同的话。但我不明白为什么它没有被调用。有人能帮我吗?

extend HttpClient

HttpClient是一个围绕HttpMessageHandler实现(通常是HttpClientHandler，其属性支持大多数运行时实现的特性)的薄包装

实际上有一个HttpMessageHandler基类用于装饰器，如您的重试场景，DelegatingHandler，您可以这样实现:

类似:

public class RetryMessageHandler : DelegatingHandler
{
    readonly int retryCount;
    public RetryMessageHandler(int retryCount)
        : this(new HttpClientHandler(), retryCount)
    {
    }
    public RetryMessageHandler(HttpMessageHandler innerHandler, int retryCount)
        : base(innerHandler)
    {
        this.retryCount = retryCount;
    }
    public override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        HttpResponseMessage response = null;
        for (int i = 0; i<=retryCount; i++)
        {
            response = await base.SendAsync(request, cancellationToken);
            if (response.IsSuccessStatusCode)
            {
                return response;
            }
        }
        return response;
    }
}

你可以这样使用:

HttpClient httpClient = HttpClientFactory.CreatePipeline(new HttpClientHandler(), 
    new [] { new RetryMessageHandler(3) });
var response = await httpClient.SendAsync(request);

另外，我建议你的EmailClient包装/依赖于HttpClient，而不是扩展它。

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