例子：

import { Injectable } from '@angular/core';@Injectable({providedIn: 'root',}) export abstract class HttpErrorHandler{abstract handleError(): void; }@Injectable({providedIn: 'root',}) export class UnKnownHandler {handleError(){console.log('UnknownHandler works');} }@Injectable({providedIn: 'root',}) export class BadGatewayHandler {handleError(){console.log('BadGatewayHandlers works');} }

app.module.ts里的providers聲明：

運行時報錯：

main.ts:12 Error: Cannot instantiate cyclic dependency! HttpErrorHandler
at throwCyclicDependencyError (core.js:8104)
at R3Injector.hydrate (core.js:17203)
at R3Injector.get (core.js:16957)
at injectInjectorOnly (core.js:941)
at ??inject (core.js:951)
at Object.factory (core.js:17383)
at R3Injector.hydrate (core.js:17207)
at R3Injector.get (core.js:16957)
at injectInjectorOnly (core.js:941)
at ??inject (core.js:951)

hydrate(token, record) {if (record.value === CIRCULAR) {throwCyclicDependencyError(stringify(token));}else if (record.value === NOT_YET) {record.value = CIRCULAR;record.value = (/** @type {?} */ (record.factory))();}if (typeof record.value === 'object' && record.value && hasOnDestroy(record.value)) {this.onDestroy.add(record.value);}return (/** @type {?} */ (record.value));}

此處進行的報錯：

更多Jerry的原創文章，盡在：“汪子熙”:

總結

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