问题描述
@SkipSelf 装饰器告诉 DI 从父注入器开始在整个树中查找依赖项
我遇到了@SkipSelf 装饰器,如下所示。在这种情况下,这个@SkipSelf
装饰器究竟是什么意思?
class Dependency {}
@Injectable()
class NeedsDependency {
constructor(@SkipSelf() public dependency: Dependency) { this.dependency = dependency; }
}
const parent = ReflectiveInjector.resolveAndCreate([Dependency]);
const child = parent.resolveAndCreateChild([NeedsDependency]);
expect(child.get(NeedsDependency).dependency instanceof Dependency).toBe(true);
const inj = ReflectiveInjector.resolveAndCreate([Dependency,NeedsDependency]);
expect(() => inj.get(NeedsDependency)).toThrowError();
解决方法
让我们一行一行地开始:
第一种情况:
A. 创建父注入器并向其添加 Dependency
:
const parent = ReflectiveInjector.resolveAndCreate([Dependency]);
B. 创建子注入器并添加NeedsDependency
,由于父注入器中提供了Dependency
,DI框架可以解析NeedsDependency
的依赖(Dependency
)
const child = parent.resolveAndCreateChild([NeedsDependency]);
第二种情况:
A. 创建一个注入器并向其添加 Dependency
和 NeedsDependency
:
const inj = ReflectiveInjector.resolveAndCreate([Dependency,NeedsDependency]);
B. 这次解析 NeedsDependency
的依赖会失败,因为 @SkipSelf()
被应用于 Dependency
,DI 框架将忽略 {{1} Dependency
注入器中的 inj
实例,并尝试在层次结构中查找满足此不存在的依赖项的提供程序,因此 inj.get(NeedsDependency)
将抛出错误,因为 NeedsDependency
可以'无法解决。
expect(() => inj.get(NeedsDependency)).toThrowError();