如何解决Blazor组件渲染时API 404未处理异常问题？

我在Blazor页面中调用API，当ApplicationID存在时可正常显示；当ApplicationID不存在时，Chrome控制台会抛出“Unhandled exception rendering component: Response status code does not indicate success: 404 (Not Found)”错误，且请求无法返回结果。

服务端代码 #

[ApiController]
[Route("api/biographicdata/{applicationid}")]
public class BiographicDataController : ControllerBase
{

    private readonly IMediator _mediator;

    public BiographicDataController(IMediator mediator)
    {
        _mediator = mediator;
    }
    [HttpGet]
    public async Task<IActionResult> Get([FromRoute] long applicationid)
    {
        var response = await _mediator.Send(new GetBiographicData.Request { ApplicationID = applicationid });
        if (string.IsNullOrEmpty(response.ErrorMessage))
        {
            return Ok(response);
        }
        else
        {
            return NotFound(response);
        }
    }

    public async Task<BiographicData> Handle(Request request, CancellationToken cancellationToken)
    {
        var result = await _db.Applications.Include(a => a.Applicant).Where(a => a.ApplicationId == request.ApplicationID)
            .Select(x => new BiographicData
            {
                ApplicantId = x.ApplicantId,
            }).FirstOrDefaultAsync(cancellationToken);
        if (result == null)
        {
            result = new BiographicData()
            {
                ErrorMessage = $"The requested Application ID {request.ApplicationID} was not found.",
            };
        }
        return result;
    }

}

Blazor客户端代码 #

protected override async Task OnInitializedAsync()
{
    AppState.UpdateApplicationID(this, appid);
    AppState.UpdateHelpURL(this, "Biographic_Information");
    var client = await _factory.CreateClientAsync();
    var result = await client.GetFromJsonAsync<BiographicData>($"api/biographicdata/{appid}");
    if (string.IsNullOrEmpty(result.ErrorMessage))
    {
      // 省略代码
    }
}

有两种实用的处理方式，可根据业务需求选择：

方式一：统一返回200状态码，用错误信息标识资源不存在 #

这种方式避免404状态码触发客户端异常，始终返回成功状态，通过返回对象的ErrorMessage传递资源不存在的信息。

修改服务端Get方法：

[HttpGet]
public async Task<IActionResult> Get([FromRoute] long applicationid)
{
    var response = await _mediator.Send(new GetBiographicData.Request { ApplicationID = applicationid });
    // 无论是否找到资源，都返回200状态码
    return Ok(response);
}

修改后Blazor端的GetFromJsonAsync能正常获取结果，继续执行后续的错误判断逻辑，不会抛出未处理异常。

方式二：保留404状态码，客户端主动捕获异常处理 #

如果要遵循REST规范（用HTTP状态码明确表示资源不存在），需要在Blazor端捕获HttpRequestException并处理404场景。

修改Blazor端代码：

protected override async Task OnInitializedAsync()
{
    AppState.UpdateApplicationID(this, appid);
    AppState.UpdateHelpURL(this, "Biographic_Information");
    var client = await _factory.CreateClientAsync();
    BiographicData result = null;

    try
    {
        result = await client.GetFromJsonAsync<BiographicData>($"api/biographicdata/{appid}");
        if (string.IsNullOrEmpty(result?.ErrorMessage))
        {
            // 正常业务逻辑代码
        }
    }
    catch (HttpRequestException ex) when (ex.StatusCode == System.Net.HttpStatusCode.NotFound)
    {
        // 处理资源不存在的情况，比如初始化错误对象或提示用户
        result = new BiographicData()
        {
            ErrorMessage = $"The requested Application ID {appid} was not found."
        };
    }

    // 后续基于result的业务逻辑
}

服务端的NotFound返回逻辑可以保持不变，因为客户端已经能捕获并处理该异常。

补充说明 #

• 方式一更适合前端不想额外处理HTTP异常的场景，逻辑更统一；
• 方式二更符合RESTful API设计原则，通过状态码传递资源状态信息。

内容的提问来源于stack exchange，提问作者user22019322