我有一个名为ServiceConfiguration的服务,它有一个非默认的ctor.我正在尝试使用工厂方法通过Autofac注册它:
builder.Register(c=>LoadConfiguration())
.As<ServiceConfiguration>();
这是简单的LoadConfiguration方法:
private ServiceConfiguration LoadConfiguration() {
const string fileName = "app.json";
var json = File.ReadAllText(fileName, Encoding.UTF8);
var model = JsonConvert.DeserializeObject<ServiceConfiguration>(json);
return model;
}
我希望Autofac在我要求解析ServiceConfiguration时调用LoadConfiguration.但它似乎试图在ServiceConfiguration上调用ctor.例如.叫这行:
var c = container.Resolve<ServiceConfiguration>();
导致此错误:
Autofac.Core.DependencyResolutionException: ‘An error occurred during
the activation of a particular registration. See the inner exception
for details. Registration: Activator = ServiceConfiguration
(ReflectionActivator), Services = [ServiceConfiguration], Lifetime =
Autofac.Core.Lifetime.CurrentScopeLifetime, Sharing = Shared,
Ownership = OwnedByLifetimeScope’
而InnerException是:
DependencyResolutionException: None of the constructors found with
‘Autofac.Core.Activators.Reflection.DefaultConstructorFinder’ on type
‘ServiceConfiguration’ can be invoked with the available services and
parameters:
Cannot resolve parameter ‘JobsConfiguration jobs’ of constructor ‘Void .ctor(JobsConfiguration)’.
你能找到我错过的东西吗?
更新:
我没有错过JobsConfiguration的注册.实际上它不是可注册类型,我不想注册它.我根本不想调用ctor(服务是从json文件构建的),而是每当有人要求ServiceConfiguration时我都希望Autofac调用LoadConfiguration()并使用它的返回值.
UPDATE2:
过了一会儿,似乎从ServiceConfiguration中提取了一个接口 – 比如IServiceConfiguration – 并且注册/解析接口工作得很好.但我无法弄清楚为什么!我是说这个:
builder.Register(c=>LoadConfiguration())
.As<IServiceConfiguration>();
var c = container.Resolve<IServiceConfiguration>();
作品.但具体版本没有.所以为什么?有什么不同?
最佳答案 您应该努力将配置文件的加载与对象组合分开.这意味着在调用Resolve时最好不要加载配置.改变这一点是微不足道的:
ServiceConfiguration configuration = LoadConfiguration();
builder.RegisterInstance(configuration);
也就是说,您的注册应该有效:
builder.Register(c => LoadConfiguration())
.As<ServiceConfiguration>();
这与:
builder.Register(c => LoadConfiguration());
通过此注册,Autofac不会自动连接ServiceConfiguration构造函数,但会将其保留给提供的委托.你的帖子没有显示可能会发生一些事情.
我使用以下MCVE,使用Autofav 4.8.1来验证这是否有效:
class ServiceConfiguration
{
public ServiceConfiguration(int a, double b) => Console.WriteLine("ctor called.");
}
static ServiceConfiguration LoadConfiguration() => new ServiceConfiguration(2, 6);
static void Main(string[] args)
{
var builder = new ContainerBuilder();
builder.Register(_ => LoadConfiguration()).As<ServiceConfiguration>();
builder.Build().Resolve<ServiceConfiguration>();
}
最后请注意:确保ServiceConfiguration不是注入许多使用者的应用程序范围的配置类.要了解应用程序范围配置类的错误,请阅读this Q/A.