我有以下代码:

app.module.ts:

NgModule({
    declarations: [
        AppComponent
    ],
    imports: [
        RouterModule,
        BrowserModule,
        ReactiveFormsModule,
        FormsModule,
        HttpModule,
        AppRoutingModule // Routes
    ],
    providers: [ // services
        AppLog,
        {provide: ErrorHandler, useClass: MyErrorHandler}
    ],
    bootstrap: [AppComponent]
})
export class AppModule {}

MyErrorHandler.ts:

@Injectable()
export class MyErrorHandler implements ErrorHandler {
  constructor (private _appLog: AppLog) {}

  handleError(error:any):void {
    let errorMessage: string = "" + error
    this._appLog.logMessageAsJson(errorMessage, "error")
            .subscribe(
              ...
            )
  }
}

appLog.ts

@Injectable()
export class AppLog {
    constructor (private _http: Http) {}

    logMessageAsJson(message: string, type: string) {
        let headers = new Headers({ "Content-Type": "application/json" })
        let jsonMessage = {"type": type, "message": message}

        return this._http.post(JSON.stringify(jsonMessage), headers)
    }
}

但是,当我的应用程序启动时,如果我在MyErrorHandler中注入(inject)了以下错误,它将失败:

Unhandled Promise rejection: Provider parse errors:
Cannot instantiate cyclic dependency!

如果我确实删除了constructor (private _appLog: AppLog) {},然后在handleError中执行了其他操作,则它可以正常工作,并调用ErrorHandler。

我猜这不起作用,因为同时实例化了AppLog和MyErrorHandler

最佳答案

您可以使用此替代方法来解决与DI的循环依赖性

@Injectable()
export class MyErrorHandler implements ErrorHandler {
  private _appLog: AppLog;
  constructor (injector:Injector) {
    setTimeout(() => this._appLog = injector.get(AppLog));
  }
  ...
}

Angulars DI本身只是不支持循环依赖性。

关于angular - 在自定义ErrorHandler中注入(inject)服务会导致 “Cannot instantiate cyclic dependency!”错误,如何解决此问题?,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/41585863/

10-09 17:37