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1、依赖注入概念详解
2、ASP.NET Core 源码解析
当一个类A完成某个任务需要另一个类B来帮助时,A就对B产生了依赖
例如CustomerController需要对customer进行新增或查找时用到EF,则对EF的Context产生了依赖
var context = new CustomerContext(new DbContextOptions<CustomerContext>{});
显示依赖:把一个类用到的所有外部组件放到一个类最上面,在构造函数里面初始化
private CustomerContext _context;
public CustomerController()
{
_context = new CustomerContext(new DbContextOptions<CustomerContext>{});
}
隐式依赖:需要用到的地方再初始化,不推荐
var context = new CustomerContext(new DbContextOptions<CustomerContext>{});
依赖高层业务,不依赖低层业务的具体实现,而依赖于具体的抽象
CustomerController是高层业务的一个组件,依赖于CustomerContext是一个低层数据库的实现,如果现在需要把EF换成一个内存的实现或者mysql,需要修改CustomerController类,风险很大,所以应该依赖于低层业务的抽象
把低层业务方法抽象,比如查找,新增,抽象出一个接口,当不需要使用EF的时候,使用内存的实现替换
private ICustomerRepository _customerRepository;
public CustomerController()
{
_customerRepository = new EfCustomerRepository(
new CustomerContext(new DbContextOptions<CustomerContext>{}));
}
实现依赖注入的方式不由自己决定,而是交给一个IOC容器,需要什么由容器传入,比如生产环境需要使用EF,则由容器传入一个EfCustomerRepository,而测试环境需要使用内存级别的,则传入一个MemoryCustomerRepository
private ICustomerRepository _customerRepository;
public CustomerController(ICustomerRepository customerRepository)
{
_customerRepository = customerRepository;
}
var repository = new Data.MemoryCustomerRepository();
var controller = new CustomerController(repository);// 通过外部控制Controller里面的依赖
var customer = new Model.Customer()
{
FirstName = "Mingson",
LastName = "Zheng",
Phone = "123456789",
};
var result = controller.Add(customer);
Assert.IsType<OkResult>(result);// 正确结果
var resultBad = controller.Add(customer);
Assert.IsType<BadRequestObjectResult>(resultBad);// 错误结果
通过单元测试可以得知修改Bug过程中是否误删代码,导致原来通过的测试现在无法通过。
Microsoft.AspNetCore.Hosting.WebHostBuilder
/// <summary>
/// Builds the required services and an <see cref="T:Microsoft.AspNetCore.Hosting.IWebHost" /> which hosts a web application.
/// </summary>
public IWebHost Build()
{
......
// 第一步,build
IServiceCollection serviceCollection1 = this.BuildCommonServices(out hostingStartupErrors);
// 第二步,获取ServiceCollection,ServiceProvider
IServiceCollection serviceCollection2 = serviceCollection1.Clone();
IServiceProvider providerFromFactory = GetProviderFromFactory(serviceCollection1);
......
// 第三步,new一个WebHost,传入ServiceCollection,ServiceProvider
WebHost webHost = new WebHost(serviceCollection2, providerFromFactory, this._options, this._config, hostingStartupErrors);
......
// 第四步,webHost初始化方法Initialize
webHost.Initialize();
......
}
第一步BuildCommonServices中new一个ServiceCollection就是在startup接口中使用
private IServiceCollection BuildCommonServices(
out AggregateException hostingStartupErrors)
{
......
ServiceCollection services = new ServiceCollection();
// new完之后添加一些初始化操作
......
return (IServiceCollection) services;
}
IStartup接口
namespace Microsoft.AspNetCore.Hosting
{
public interface IStartup
{
IServiceProvider ConfigureServices(IServiceCollection services);
void Configure(IApplicationBuilder app);// 配置管道
}
}
第四步,webHost初始化方法Initialize
public void Initialize()
{
......
this.EnsureApplicationServices();
......
}
private void EnsureApplicationServices()
{
......
this.EnsureStartup();
this._applicationServices = this._startup.ConfigureServices(this._applicationServiceCollection);
}
private void EnsureStartup()
{
if (this._startup != null)
return;
this._startup = this._hostingServiceProvider.GetService<IStartup>();
if (this._startup == null)
throw new InvalidOperationException(string.Format("No startup configured. Please specify startup via WebHostBuilder.UseStartup, WebHostBuilder.Configure, injecting {0} or specifying the startup assembly via {1} in the web host configuration.", (object) "IStartup", (object) "StartupAssemblyKey"));
}
了解ASP.NET Core 依赖注入,看这篇就够了:
http://www.jessetalk.cn/2017/11/06/di-in-aspnetcore/