源码分析——服务提供之三种获取实例的区别

如果服务未注册则GetService()返回null，GetRequiredService()而是抛出异常。

public static T GetService<T>(this IServiceProvider provider)
{
    if (provider == null)
    {
        throw new ArgumentNullException(nameof(provider));
    }

    return (T)provider.GetService(typeof(T));
}

public static object GetRequiredService(this IServiceProvider provider, Type serviceType)
{
    if (provider == null)
    {
        throw new ArgumentNullException(nameof(provider));
    }

    if (serviceType == null)
    {
        throw new ArgumentNullException(nameof(serviceType));
    }

    var requiredServiceSupportingProvider = provider as ISupportRequiredService;
    if (requiredServiceSupportingProvider != null)
    {
        return requiredServiceSupportingProvider.GetRequiredService(serviceType);
    }

    var service = provider.GetService(serviceType);
    if (service == null)
    {
        throw new InvalidOperationException(Resources.FormatNoServiceRegistered(serviceType));
    }

    return service;
}

public static T GetRequiredService<T>(this IServiceProvider provider)
{
    if (provider == null)
    {
        throw new ArgumentNullException(nameof(provider));
    }

    return (T)provider.GetRequiredService(typeof(T));
}