Blazor HttpClient卡在GetAsync中 [英] Blazor HttpClient stuck in GetAsync

问题描述

我正在针对Blazor 3.0.0-preview4-19216-03的Client Blazor应用中进行测试

I'm making test in a Client Side Blazor app targeting Blazor 3.0.0-preview4-19216-03

剃须刀页面:

@page "/counter"
@using BlazorServiceTest
@inject IWebCrawlServiceAsync WebCrawler

<h1>Counter</h1>

<p>Current count: @debug</p>

<button class="btn btn-primary" onclick="@IncrementCount">Click me</button>

@functions {
    string debug = "";

    async void IncrementCount()
    {
        debug = await WebCrawler.GetWeb();
    }
}

依赖注入:

using BlazorServiceTest;
using Microsoft.AspNetCore.Components.Builder;
using Microsoft.Extensions.DependencyInjection;

namespace BlazorServicesTest
{
    public class Startup
    {
        public void ConfigureServices(IServiceCollection services)
        {   
            services.AddSingleton<IWebCrawlServiceAsync, WebCrawlServiceAsync>();            
        }

        public void Configure(IComponentsApplicationBuilder app)
        {
            app.AddComponent<App>("app");
        }
    }
}

服务:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Threading.Tasks;

namespace BlazorServiceTest
{
    public interface IWebCrawlServiceAsync
    {
        Task<string> GetWeb();
    }

    public class WebCrawlServiceAsync : IWebCrawlServiceAsync
    {
        private HttpClient _client;    

        public WebCrawlServiceAsync(HttpClient client)
        {
            _client = client;
        }

        public async Task<string> GetWeb()
        {
            var response = await _client.GetAsync("https://postman-echo.com/response-headers?foo1=bar1&foo2=bar2");
            var result = await response.Content.ReadAsStringAsync();
            return result;
        }
    }
}

每当我单击增量"时，都不会发生任何事情，并且对GetWeb的服务调用被卡在GetAsync调用中.

Whenever I click in Increment count nothing happens and the service call to GetWeb it's stuck in the GetAsync call.

更新

如果我在Chrome的WASM调试器中调试WebCrawler服务，则会发出他的请求

If I debug the service WebCrawler in Chrome's WASM debugger, he request is being made

但是响应部分为空:

推荐答案

在客户端应用中，您只能访问自己的来源或支持CORS的网站.

From a client-side app you can only acces your own origin or sites that support CORS.

为了验证这是您的问题，可以尝试使用https://postman-echo.com/response-headers?foo1=bar1&access-control-allow-origin=*，它可能会起作用.

In order to verify that this is your issue, you can try https://postman-echo.com/response-headers?foo1=bar1&access-control-allow-origin=*, that might work.

但是它仅适用于该站点.通常，您无法控制响应头.这不是解决方法.

But it will only work for that site. You normally have no control over the response headers. It's not a fix.

因此，对于网络爬虫来说，Blazor客户端不是一个好的平台. JS或WASM上的任何应用程序也是如此.

So, Blazor client-side is just not a good platform for a webcrawler. The same goes for any app on JS or WASM.

Blazor服务器端应该没有问题.或使用Web API服务.

Blazor server-side should have no problems. Or use a Web API service.

这篇关于Blazor HttpClient卡在GetAsync中的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！