无法在 Blazor 中调用 Web API

Question

调用 API 时出现以下错误。已测试 API 是否以 JSON 格式返回数据。

Microsoft.AspNetCore.Components.WebAssembly.Rendering.WebAssemblyRenderer[100] 未处理的异常渲染组件：net_http_client_http_browser_baseaddress_required Arg_ParamName_Name, requestUri System.ArgumentException：net_http_client_http_browser_baseaddress_required Arg_ParamName_Name，requestUri 在 System.Net.Http.HttpRequestMessage.InitializeValues（HttpMethod 方法，Uri requestUri） 在 System.Net.Http.HttpRequestMessage..ctor（HttpMethod 方法，Uri requestUri） 在 System.Net.Http.HttpClient.CreateRequestMessage（HttpMethod 方法，Uri uri） 在 System.Net.Http.HttpClient.GetAsync（Uri requestUri，HttpCompletionOption 完成选项，CancellationToken 取消令牌） 在 System.Net.Http.HttpClient.GetAsync（字符串 requestUri，HttpCompletionOption 完成选项，CancellationToken 取消令牌） 在 System.Net.Http.Json.HttpClientJsonExtensions.GetFromJsonAsync[StudentAdmission[]]（HttpClient 客户端，字符串 requestUri，JsonSerializerOptions 选项，CancellationToken cancelToken） 在 System.Net.Http.Json.HttpClientJsonExtensions.GetFromJsonAsync[StudentAdmission[]]（HttpClient 客户端，字符串 requestUri，CancellationToken cancelToken） 在 BlazorApp1.Pages.FetchData.OnInitializedAsync() 在 Microsoft.AspNetCore.Components.ComponentBase.RunInitAndSetParametersAsync()

Blazor 页面：
@page "/fetchdata" @inject HttpClient Http

<h1>Weather forecast</h1>

<p>This component demonstrates fetching data from the server.</p>

@if (studentAdmissions == null)
{
    <p><em>Loading...</em></p>
}
else
{
    <table class="table">
        <thead>
            <tr>
                <th>FirstName</th>
                <th>LastName (C)</th>
                <th>Gender (F)</th>
                <th>Mobile</th>
            </tr>
        </thead>
        <tbody>
            @foreach (var forecast in studentAdmissions)
            {
                <tr>
                    <td>@forecast.FirstName</td>
                    <td>@forecast.LastName</td>
                    <td>@forecast.Gender</td>
                    <td>@forecast.Mobile</td>
                </tr>
            }
        </tbody>
    </table>
}

@code {
 
    private List<StudentAdmission> studentAdmissions=new List<StudentAdmission>() ;
    protected override async Task OnInitializedAsync()
    {
        studentAdmissions = await Http.GetFromJsonAsync<List<StudentAdmission>>("https://schoolwebapi.azurewebsites.net/api/StudentAdmissions");
    }


    
    public class StudentAdmission
    {
        public int Id { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Gender { get; set; }
        public System.DateTime DateOfBirth { get; set; }
        public string Email { get; set; }
        public string FatherName { get; set; }
        public string Mobile { get; set; }
        public string Standard { get; set; }
        public string PreviousOrganization { get; set; }
        public string CommunicationAddress { get; set; }
        public string PermanentAddress { get; set; }
        public double AdmissionFee { get; set; }
    }
}

**WebApiConfig:**

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web.Http;

namespace StudnetManagementSystemAPI
{
    public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            // Web API configuration and services

            // Web API routes
            config.EnableCors();
            config.MapHttpAttributeRoutes();

            config.Routes.MapHttpRoute(
                name: "DefaultApi",
                routeTemplate: "api/{controller}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );
            config.IncludeErrorDetailPolicy = IncludeErrorDetailPolicy.Always;
            var appXmlType = config.Formatters.XmlFormatter.SupportedMediaTypes.FirstOrDefault(t => t.MediaType == "application/xml");
            config.Formatters.XmlFormatter.SupportedMediaTypes.Remove(appXmlType);
        }
    }
}

**Controller:**
    using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Entity;
using System.Data.Entity.Infrastructure;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Threading.Tasks;
using System.Web.Http;
using System.Web.Http.Description;
using StudnetManagementSystemAPI.Models;
using System.Web.Http.Cors;

namespace StudnetManagementSystemAPI.Controllers
{
    [EnableCors(origins: "http://schoolwebapi.azurewebsites.net", headers: "*", methods: "*")]
    public class StudentAdmissionsController : ApiController
    {




  You can Refer the below Blazor WebAssemly in Azure
    https://blazorapp120210607194704.azurewebsites.net/fetchdata

AzureCors

Answer 1

您的 EnableCors 属性中的来源不正确。您已经获得了 webapi (http://schoolwebapi.azurewebsites.net) 的网址，而它应该是调用它的网站的网址：

[EnableCors(origins: "https://blazorapp120210607194704.azurewebsites.net", headers: "*", methods: "*")]