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@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装饰器到底意味着什么？

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();
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1 回答 1

0

让我们逐行开始：

第一种情况：

A.创建父注入器并添加Dependency到它：

const parent = ReflectiveInjector.resolveAndCreate([Dependency]);

B.创建子注入器并添加NeedsDependency到它，由于Dependency在父注入器中提供，DI框架可以解决NeedsDependency依赖关系（Dependency）

const child = parent.resolveAndCreateChild([NeedsDependency]);

第二种情况：

A.创建一个注入器并将Dependency&添加NeedsDependency到它：

const inj = ReflectiveInjector.resolveAndCreate([Dependency, NeedsDependency]);

B.这次解析NeedsDependency的依赖会失败，因为@SkipSelf()被应用到了Dependency，DI框架会忽略injector中的Dependency实例inj，并尝试查找层次结构来找到一个满足这个不存在的依赖的provider，因此inj.get(NeedsDependency)会抛出一个NeedsDependency无法解决的错误。

expect(() => inj.get(NeedsDependency)).toThrowError();
于 2020-12-28T17:12:35.723 回答