理解 IOC 容器

没有使用 IOC 容器时：

使用 IOC 容器时：

去掉 IOC 容器时：

IOC容器又像一个插座，将电输送到需要的每一处。需要充电的话，就连接，不需要就不连接，节省资源，不用时时刻刻连上电源了。

使用IOC容器的好处：

1) 可维护性比较好

2) 便于单元测试，调试程序和诊断故障

2) 可复用性好

实现组件之间的解耦，提高程序的灵活性和可维护性

AutoFac使用方法总结：

AutoFac 是 .net 平台下的 IOC 容器产品，它可以管理类之间的复杂的依赖关系。在使用方面主要是 register 和 resolve 两类操作。这里用单元测试的形式列举了 AutoFac 的常用使用方法：

一、注册

使用 RegisterType 进行注册

[Fact]
public void can_resolve_myclass()
{
    var builder = new ContainerBuilder();
    builder.RegisterType<MyClass>();

    IContainer container = builder.Build();
    var myClass = container.Resolve<MyClass>();
    Assert.NotNull(myClass);
}

注册为接口

[Fact]
public void register_as_interface()
{
    var builder = new ContainerBuilder();
    builder.Register(c => new MyClass()).As<MyInterface>();
 
    IContainer container = builder.Build();
    Assert.NotNull(container.Resolve<MyInterface>());
    Assert.Throws(typeof (ComponentNotRegisteredException), () => container.Resolve<MyClass>());
}

使用lambda表达式进行注册

[Fact]
public void can_register_with_lambda()
{
    var builder = new ContainerBuilder();
    builder.Register(c => new MyClass());

    IContainer container = builder.Build();
    var myClass = container.Resolve<MyClass>();
    Assert.NotNull(myClass);
}

带构造参数的注册

[Fact]
public void register_with_parameter()
{
    var builder = new ContainerBuilder();
    builder.Register(c => new MyParameter());
    builder.Register(c => new MyClass(c.Resolve<MyParameter>()));
    IContainer container = builder.Build();
    Assert.NotNull(container.Resolve<MyClass>());
}

带属性赋值的注册

[Fact]
public void register_with_property()
{
    var builder = new ContainerBuilder();
    builder.Register(c => new MyProperty());
    builder.Register(
        c => new MyClass()
        {
            Property = c.Resolve<MyProperty>()
        });
    IContainer container = builder.Build();
    var myClass = container.Resolve<MyClass>();
    Assert.NotNull(myClass);
    Assert.NotNull(myClass.Property);
}

Autofac分离了类的创建和使用，这样可以根据输入参数（NamedParameter）动态的选择实现类。

[Fact]
public void select_an_implementer_based_on_parameter_value()
{
    var builder = new ContainerBuilder();
    builder.Register<IRepository>((c, p) =>
    {
        var type = p.Named<string>("type");
        if (type == "test")
        {
            return new TestRepository();
        }
        else
        {
            return new DbRepository();
        }
    }).As<IRepository>();

    IContainer container = builder.Build();
    var repository = container.Resolve<IRepository>(new NamedParameter("type", "test"));
    Assert.Equal(typeof(TestRepository), repository.GetType());
}

AufoFac也可以用一个实例来注册，比如用在单例模式情况下：

[Fact]
public void register_with_instance()
{
    var builder = new ContainerBuilder();
    builder.RegisterInstance(MyInstance.Instance).ExternallyOwned();
    IContainer container = builder.Build();
    var myInstance1 = container.Resolve<MyInstance>();
    var myInstance2 = container.Resolve<MyInstance>();
    Assert.Equal(myInstance1, myInstance2);
}

注册open generic类型

[Fact]
public void register_open_generic()
{
    var builder = new ContainerBuilder();
    builder.RegisterGeneric(typeof(MyList<>));
    IContainer container = builder.Build();
    var myIntList = container.Resolve<MyList<int>>();
    Assert.NotNull(myIntList);
    var myStringList = container.Resolve<MyList<string>>();
    Assert.NotNull(myStringList);
}

对于同一个接口，后面注册的实现会覆盖之前的实现

[Fact]
public void register_order()
{
    var containerBuilder = new ContainerBuilder();
    containerBuilder.RegisterType<DbRepository>().As<IRepository>();
    containerBuilder.RegisterType<TestRepository>().As<IRepository>();

    IContainer container = containerBuilder.Build();
    var repository = container.Resolve<IRepository>();
    Assert.Equal(typeof(TestRepository), repository.GetType());
}

如果不想覆盖的话，可以用PreserveExistingDefaults，这样会保留原来注册的实现。

[Fact]
public void register_order_defaults()
{
    var containerBuilder = new ContainerBuilder();
    containerBuilder.RegisterType<DbRepository>().As<IRepository>();
    containerBuilder.RegisterType<TestRepository>().As<IRepository>().PreserveExistingDefaults();

    IContainer container = containerBuilder.Build();
    var repository = container.Resolve<IRepository>();
    Assert.Equal(typeof(DbRepository), repository.GetType());
}

可以用Name来区分不同的实现，代替As方法

[Fact]
public void register_with_name()
{
    var containerBuilder = new ContainerBuilder();
    containerBuilder.RegisterType<DbRepository>().Named<IRepository>("DB");
    containerBuilder.RegisterType<TestRepository>().Named<IRepository>("Test");

    IContainer container = containerBuilder.Build();
    var dbRepository = container.ResolveNamed<IRepository>("DB");
    var testRepository = container.ResolveNamed<IRepository>("Test");
    Assert.Equal(typeof(DbRepository), dbRepository.GetType());
    Assert.Equal(typeof(TestRepository), testRepository.GetType());
}

如果一个类有多个构造函数的话，可以在注册时候选择不同的构造函数

[Fact]
public void choose_constructors()
{
    var builder = new ContainerBuilder();
    builder.RegisterType<MyParameter>();
    builder.RegisterType<MyClass>().UsingConstructor(typeof(MyParameter));
    IContainer container = builder.Build();
    var myClass = container.Resolve<MyClass>();
    Assert.NotNull(myClass);
}

AutoFac可以注册一个Assemble下所有的类，当然，也可以根据类型进行筛选

[Fact]
public void register_assembly()
{
    var builder = new ContainerBuilder();
    builder.RegisterAssemblyTypes(Assembly.GetExecutingAssembly()).
        Where(t => t.Name.EndsWith("Repository")).
        AsImplementedInterfaces();

    IContainer container = builder.Build();
    var repository = container.Resolve<IRepository>();
    Assert.NotNull(repository);
}

二、事件

AutoFac支持三种事件：OnActivating，OnActivated，OnRelease。OnActivating在注册组件使用之前会被调用，此时可以替换实现类或者进行一些其他的初始化工作，OnActivated在实例化之后会被调用，OnRelease在组件释放之后会被调用。

public class MyEvent : IDisposable
{
    public MyEvent(string input)
    {
        Console.WriteLine(input);
    }

    public MyEvent()
    {
        Console.WriteLine("Init");
    }

    public void Dispose()
    {
        Console.WriteLine("Dispose");
    }
}

public void test_event()
{
    var builder = new ContainerBuilder();
    builder.RegisterType<MyEvent>().
        OnActivating(e => e.ReplaceInstance(new MyEvent("input"))).
        OnActivated(e => Console.WriteLine("OnActivated")).
        OnRelease(e => Console.WriteLine("OnRelease"));


    using (IContainer container = builder.Build())
    {
        using (var myEvent = container.Resolve<MyEvent>())
        {
        }
    }
}

此时的输出为：

Init
input
OnActivated
Dispose
OnRelease

利用事件可以在构造对象之后调用对象的方法：

[Fact]
public void call_method_when_init()
{
    var builder = new ContainerBuilder();
    builder.RegisterType<MyClassWithMethod>().OnActivating(e => e.Instance.Add(5));
    IContainer container = builder.Build();
    Assert.Equal(5, container.Resolve<MyClassWithMethod>().Index);
}
public class MyClassWithMethod
{
    public int Index { get; set; }
    public void Add(int value)
    {
        Index = Index + value;
    }
}

三、循环依赖

循环依赖是个比较头疼的问题，在AutoFac中很多循环依赖的场景不被支持：

public class ClassA
{
    private readonly ClassB b;

    public ClassA(ClassB b)
    {
        this.b = b;
    }
}

public class ClassB
{
    public ClassA A { get; set; }

}

[Fact]
public void circular_dependencies_exception()
{
    var builder = new ContainerBuilder();
    builder.Register(c => new ClassB() { A = c.Resolve<ClassA>() });
    builder.Register(c => new ClassA(c.Resolve<ClassB>()));
    IContainer container = builder.Build();
    Assert.Throws(typeof(DependencyResolutionException), () => container.Resolve<ClassA>());
}

可以部分的解决这种循环依赖的问题，前提是ClassA和ClassB的生命周期不能都是InstancePerDependency

[Fact]
public void circular_dependencies_ok()
{
    var builder = new ContainerBuilder();
    builder.RegisterType<ClassB>().
        PropertiesAutowired(PropertyWiringFlags.AllowCircularDependencies).SingleInstance();
    builder.Register(c => new ClassA(c.Resolve<ClassB>()));
    IContainer container = builder.Build();
    Assert.NotNull(container.Resolve<ClassA>());
    Assert.NotNull(container.Resolve<ClassB>());
    Assert.NotNull(container.Resolve<ClassB>().A);
}

四、生命周期

AutoFac中的生命周期概念非常重要，AutoFac也提供了强大的生命周期管理的能力。

AutoFac定义了三种生命周期：

Per Dependency
Single Instance
Per Lifetime Scope

Per Dependency为默认的生命周期，也被称为’transient’或’factory’，其实就是每次请求都创建一个新的对象

[Fact]
public void per_dependency()
{
    var builder = new ContainerBuilder();
    builder.RegisterType<MyClass>().InstancePerDependency();
    IContainer container = builder.Build();
    var myClass1 = container.Resolve<MyClass>();
    var myClass2 = container.Resolve<MyClass>();
    Assert.NotEqual(myClass1, myClass2);
}

Single Instance也很好理解，就是每次都用同一个对象

[Fact]
public void single_instance()
{
    var builder = new ContainerBuilder();
    builder.RegisterType<MyClass>().SingleInstance();

    IContainer container = builder.Build();
    var myClass1 = container.Resolve<MyClass>();
    var myClass2 = container.Resolve<MyClass>();

    Assert.Equal(myClass1, myClass2);
}

Per Lifetime Scope，同一个Lifetime生成的对象是同一个实例

[Fact]
public void per_lifetime_scope()
{
    var builder = new ContainerBuilder();
    builder.RegisterType<MyClass>().InstancePerLifetimeScope();

    IContainer container = builder.Build();
    var myClass1 = container.Resolve<MyClass>();
    var myClass2 = container.Resolve<MyClass>();

    ILifetimeScope inner = container.BeginLifetimeScope();
    var myClass3 = inner.Resolve<MyClass>();
    var myClass4 = inner.Resolve<MyClass>();

    Assert.Equal(myClass1, myClass2);
    Assert.NotEqual(myClass2, myClass3);
    Assert.Equal(myClass3, myClass4);
}

[Fact]
public void life_time_and_dispose()
{
    var builder = new ContainerBuilder();
    builder.RegisterType<Disposable>();

    using (IContainer container = builder.Build())
    {
        var outInstance = container.Resolve<Disposable>(new NamedParameter("name", "out"));

        using (var inner = container.BeginLifetimeScope())
        {
            var inInstance = container.Resolve<Disposable>(new NamedParameter("name", "in"));
        }//inInstance dispose here
    }//out dispose here
}

转自：https://www.cnblogs.com/licin/p/6560426.html

IOC 容器与 Autofac 的基本使用

AutoFac使用方法总结：

一、注册

二、事件

三、循环依赖

四、生命周期

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