在自定义ErrorHandler中注入服务会导致“无法实例化循环依赖性！".错误，我该如何解决? [英] Injecting services in custom ErrorHandler causes "Cannot instantiate cyclic dependency!" error, how can I fix this?

问题描述

我有以下代码:

app.module.ts:

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:

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

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，当我的应用程序引导时，如果我在MyErrorHandler中进行了注入并出现以下错误，它将失败:

However, when my app bootstrap, it fails if I have an injection in MyErrorHandler with the following error :

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

如果我确实删除了constructor (private _appLog: AppLog) {}，然后又在handleError中执行了其他操作，则可以正常工作，并调用了ErrorHandler.

If I do remove constructor (private _appLog: AppLog) {} and then do something else in handleError it works just fine and the ErrorHandler is called.

我猜因为AppLog和MyErrorHandler同时实例化，所以它不起作用

I guess it doesn't work as AppLog and MyErrorHandler are instantiated at the same time

推荐答案

您可以使用此替代方法来解决DI的循环依赖性

You can use this workaround to break up cyclic dependencies with DI

@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关系.

Angulars DI itself just doesn't support cyclic dependencies.

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