.NET 7中通过DI调用类时如何传递ILogger实例？

要手动实例化WeatherForecastService并传递正确的ILogger<WeatherForecastService>实例，有以下几种符合.NET DI设计的方案，按推荐优先级排序：

方案1：直接注入目标Logger到LazyLoadedWeatherForecastService #

如果LazyLoadedWeatherForecastService本身是通过依赖注入容器创建的，最直接的方式是将ILogger<WeatherForecastService>注入到它的构造函数中，后续在Create方法里直接使用：

public class LazyLoadedWeatherForecastService
{
    private readonly HttpClient _httpClient;
    private readonly ILogger<WeatherForecastService> _weatherServiceLogger;

    // 通过DI注入HttpClient和目标Logger
    public LazyLoadedWeatherForecastService(HttpClient httpClient, ILogger<WeatherForecastService> weatherServiceLogger)
    {
        _httpClient = httpClient;
        _weatherServiceLogger = weatherServiceLogger;
    }

    public WeatherForecastService Create()
    {
        // 直接传递已注入的Logger实例
        return new WeatherForecastService(_httpClient, _weatherServiceLogger);
    }
}

这种方式最贴合DI设计原则，代码清晰易维护，是首选方案。

方案2：通过ILoggerFactory创建目标Logger #

如果需要动态生成不同类型的Logger，或者无法直接注入ILogger<WeatherForecastService>，可以注入ILoggerFactory，通过它生成指定类型的Logger实例：

public class LazyLoadedWeatherForecastService
{
    private readonly HttpClient _httpClient;
    private readonly ILoggerFactory _loggerFactory;

    public LazyLoadedWeatherForecastService(HttpClient httpClient, ILoggerFactory loggerFactory)
    {
        _httpClient = httpClient;
        _loggerFactory = loggerFactory;
    }

    public WeatherForecastService Create()
    {
        // 基于LoggerFactory创建WeatherForecastService对应的Logger
        var logger = _loggerFactory.CreateLogger<WeatherForecastService>();
        return new WeatherForecastService(_httpClient, logger);
    }
}

方案3：通过IServiceProvider获取Logger（兜底方案） #

如果上述两种方式都不可行（比如LazyLoadedWeatherForecastService是手动实例化的），可以注入IServiceProvider，通过服务定位器模式获取Logger实例。但这种方式不推荐过度使用，会降低代码的可测试性和清晰度：

public class LazyLoadedWeatherForecastService
{
    private readonly HttpClient _httpClient;
    private readonly IServiceProvider _serviceProvider;

    public LazyLoadedWeatherForecastService(HttpClient httpClient, IServiceProvider serviceProvider)
    {
        _httpClient = httpClient;
        _serviceProvider = serviceProvider;
    }

    public WeatherForecastService Create()
    {
        // 从DI容器中获取ILogger<WeatherForecastService>实例
        var logger = _serviceProvider.GetRequiredService<ILogger<WeatherForecastService>>();
        return new WeatherForecastService(_httpClient, logger);
    }
}

内容的提问来源于stack exchange，提问作者Serge