[ApiDescriptionSettings]
[Route("RandomNumber2")]
public class RandomNumber2Service : IDynamicApiController
{
    [HttpGet]
    [AllowAnonymous]
    [FileResultContentType(KnownMimeTypes.Png)]
    // 这里忽略[FromServices]将415错误。
    public IActionResult Get([FromRoute] string key, [FromServices] IGVCodeManager gvcMgr) 
    {
        return new FileContentResult(gvcMgr.Create(key), KnownMimeTypes.Png);
    }
}

[ApiController]
[Route("[controller]")]
public class RandomNumberController : ControllerBase
{
    [HttpGet]
    [AllowAnonymous]
    [FileResultContentType(KnownMimeTypes.Png)]
    public IActionResult Get([FromRoute] string key, IGVCodeManager gvcMgr)
    {
        return new FileContentResult(gvcMgr.Create(key), KnownMimeTypes.Png);
    }
}