Angular 2 Promise問題

Question

我開始學習Angular 2，並且遇到了使用Promise.then從服務返回對象的問題。我目前只使用固定數組（COACHES）僞造數據庫調用。在我服務的功能如下

getCoach(id: number) { 
    return Promise.resolve(COACHES).then(
     coaches => coaches.filter(coach => coach.id == id)[0] 
    ); 
} 

然後我用這在我的coach_detail.component.ts在ngOnInit鉤來獲得主教練的對象我想用路線PARAMS：

export class CoachDetailComponent implements OnInit { 

    coach: Coach; 

    constructor(
     private _coachService: CoachService, 
     private _routeParams: RouteParams) {} 

    ngOnInit() { 
     let id = +this._routeParams.get('id'); 
     this._coachService.getCoach(id).then(coach => this.coach = coach); 
     console.log(this.coach); 
    } 
} 

我可以看到我的控制檯的承諾正在恢復回到我的組件，但是console.log(this.coach)正在恢復爲undefined

任何幫助是非常讚賞，因爲我使用了相似的邏輯在不同的組件返回教練的完整列表，並能正常工作！

Answer 1

您的console.log()在諾言鏈之前被調用。

ngOnInit() { 
    let id = +this._routeParams.get('id'); 
    this._coachService.getCoach(id).then(coach => { 
     this.coach = coach 
     console.log(this.coach); // not undefined 
    }); 
    console.log(this.coach); // undefined 
}