.NET 6非顶级语句控制台应用Serilog注入后获取实例为null

问题根源 #

AddSerilog方法仅将Serilog集成到Microsoft.Extensions.Logging抽象体系中，DI容器中注册的是Microsoft.Extensions.Logging.ILogger和Microsoft.Extensions.Logging.ILogger<T>类型，并未直接注册Serilog.ILogger。因此直接调用GetService<Serilog.ILogger>()会返回null。

解决方案 #

方案1：直接将Serilog.ILogger注册到DI容器 #

修改服务注册代码，在构建服务集合时显式添加Serilog.ILogger的单例注册：

var config = new ConfigurationBuilder()
               .AddJsonFile("appSettings.json", false, true)
               .Build();

// 先创建Serilog实例
var logger = new LoggerConfiguration()
              .MinimumLevel.Information()
              .WriteTo.File(path: "\\Logs", restrictedToMinimumLevel: LogEventLevel.Information, 
                           outputTemplate: "[{Timestamp:HH:mm:ss} {Level:u3}] {Message:lj}{NewLine}{Exception}",
                           fileSizeLimitBytes: 1000000, rollOnFileSizeLimit: true, 
                           retainedFileCountLimit: 365, retainedFileTimeLimit: new TimeSpan(365, 0, 0, 0))
              .CreateLogger();

var serviceProvider = new ServiceCollection()
                      .AddLogging(builder =>
                      {
                          builder.AddSerilog(logger);
                      })
                      .AddSingleton<Serilog.ILogger>(logger) // 新增：注册Serilog.ILogger到DI
                      .BuildServiceProvider();

// 现在可以正常获取实例
var service = serviceProvider.GetService<Serilog.ILogger>();

方案2：通过Microsoft日志抽象转换为Serilog.ILogger #

无需额外注册，先获取Microsoft的ILogger实例，再转换为Serilog.ILogger：

var serviceProvider = new ServiceCollection()
                      .AddLogging(builder =>
                      {
                          var logger = new LoggerConfiguration()
                                        .MinimumLevel.Information()
                                        .WriteTo.File(path: "\\Logs", restrictedToMinimumLevel: LogEventLevel.Information, 
                                                     outputTemplate: "[{Timestamp:HH:mm:ss} {Level:u3}] {Message:lj}{NewLine}{Exception}",
                                                     fileSizeLimitBytes: 1000000, rollOnFileSizeLimit: true, 
                                                     retainedFileCountLimit: 365, retainedFileTimeLimit: new TimeSpan(365, 0, 0, 0))
                                        .CreateLogger();
                          builder.AddSerilog(logger);
                      })
                      .BuildServiceProvider();

// 获取Microsoft ILogger并转换
var msLogger = serviceProvider.GetService<Microsoft.Extensions.Logging.ILogger>();
var serilogLogger = msLogger as Serilog.ILogger;

// 或者使用扩展方法（需确保引用Serilog.Extensions.Logging）
// var serilogLogger = msLogger.ToSerilogLogger();

推荐方案：使用Microsoft日志抽象进行依赖注入 #

.NET官方推荐依赖Microsoft.Extensions.Logging.ILogger<T>进行日志注入，Serilog会自动适配该抽象，无需直接操作Serilog.ILogger：

// 定义服务类
public class MyBusinessService
{
    private readonly ILogger<MyBusinessService> _logger;

    // 注入ILogger<T>
    public MyBusinessService(ILogger<MyBusinessService> logger)
    {
        _logger = logger;
    }

    public void Execute()
    {
        // 使用Serilog处理日志输出
        _logger.LogInformation("业务逻辑执行中");
    }
}

// 注册服务
var serviceProvider = new ServiceCollection()
                      .AddLogging(builder =>
                      {
                          var logger = new LoggerConfiguration()
                                        .MinimumLevel.Information()
                                        .WriteTo.File(path: "\\Logs", restrictedToMinimumLevel: LogEventLevel.Information, 
                                                     outputTemplate: "[{Timestamp:HH:mm:ss} {Level:u3}] {Message:lj}{NewLine}{Exception}",
                                                     fileSizeLimitBytes: 1000000, rollOnFileSizeLimit: true, 
                                                     retainedFileCountLimit: 365, retainedFileTimeLimit: new TimeSpan(365, 0, 0, 0))
                                        .CreateLogger();
                          builder.AddSerilog(logger);
                      })
                      .AddTransient<MyBusinessService>()
                      .BuildServiceProvider();

// 使用服务
var businessService = serviceProvider.GetService<MyBusinessService>();
businessService.Execute();

内容的提问来源于stack exchange，提问作者Rama