angular - 获取特定索引处可观察的数组元素 [Typescript]

Question

我正在使用 Angular4 和 angularfire2-Firestore 运行 ionic3 应用程序。

如何从 Observable 获取单个对象。我希望以 typescript 形式返回。

console.log(this.opportunity.title)  //   "Title1"

在下面的代码中，我使用 getOpportunityByIndex() 方法，并将索引作为参数。我得到以下输出，但我不确定下一步该做什么。

Observable {_isScalar: false, source: Observable, operator: MapOperator}
    operator:MapOperator {thisArg: undefined, project: ƒ}
    source:Observable {_isScalar: false, source: Observable, operator: MapOperator}
    _isScalar:false
    __proto__:Object

代码

export interface Opportunity { title: string;  }
export interface OpportunityId extends Opportunity { id: string; }

opportunities: Observable<OpportunityId[]>;

  constructor( public firebaseProvider: FirebaseProvider)   {
    this.opportunities = this.firebaseProvider.getOpportunities();
  }

  getOpportunityByIndex(index: number) {            
     this.opportunity = this.opportunities.map(arr => arr[index]);
     console.log(this.opportunity.title);
    }
}

FirebaseProvider服务

import { Injectable } from '@angular/core';
import { AngularFirestore, AngularFirestoreCollection } from 'angularfire2/firestore';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';

export interface Opportunity { title: string;  }
export interface OpportunityId extends Opportunity { id?: string; }

@Injectable()
  export class FirebaseProvider {    
  private opportunitiesCollection: AngularFirestoreCollection<OpportunityId>;
  opportunity: Opportunity

  constructor(afs: AngularFirestore) {
    this.opportunitiesCollection = afs.collection<Opportunity>('opportunities');
    this.opportunities = this.opportunitiesCollection.snapshotChanges().map(actions => {
      return actions.map(a => {
        const data = a.payload.doc.data() as Opportunity;
        const id = a.payload.doc.id;
        return { id, ...data };
      });
    });
  }

   getOpportunities() {
    return this.opportunities;
  }
}

Answer 1

据我对您的示例的了解，this.opportunities 返回一个包含机会数组的可观察值。有了这个，您只需要订阅流，然后您就可以选择参数传递的特定索引。这是您需要做的:

getOpportunityByIndex(index: number) {            
 this.opportunities
 .subscribe( opportunities => {
     this.opportunity = opportunities[index];
     console.log(this.opportunity.title);
  });

}

编辑

如果您想让它更加灵活，您可以将机会列表设为常规数组

opportunities: OpportunityId[]

然后在构造函数中执行

constructor( public firebaseProvider:FirebaseProvider)   {
    this.firebaseProvider.getOpportunities()
    .subscribe( opportunities => {
        this.opportunities = opportunities;
    });

}

然后你就可以在任何你想调用它的时候执行

getOpportunityByIndex(index: number) {            
   this.opportunity = this.opportunities[index];
   console.log(this.opportunity.title);
}