角可观未定义值

Question

我试图创建一个可观察的方法，在该方法中我返回一个String值并订阅它，但是在订阅后却没有得到返回的String值。我是Angular的新手

shared / ExamplenService.ts

theEvent(e){
  if(e.key === 'Enter') {
    this.setState({
      newTypePredefinedValue: '',
      readOnly:true
    });

    fetch(..., { ... })
      .then(res => {
        // Handle response
        this.setState({
          readOnly:false
        })
      });
  }
}

dashboard / test / TestComponent.ts

    @Injectable()
    export class ExamplenService {
    someValue: any;



      public setSomething(){
      return  return Observable.create(observer => {
      cognitoUser.authenticateUser(authenticationDetails, {
      onSuccess: function (result) {
      this.sameValue=""// Extracting some value from  a http call
       });


    public getSomething(): any {
    const studentsObservable = new Observable(observer => {
       setTimeout(() => {
           observer.next(this.sameValue);
       }, 1000);
    });

    return studentsObservable;
   }

  export class TestComponent implements OnInit
 _data : any;


constructor(private http: Http, private example: ExamplenService) {

 }

  ngOnInit() {
   const s= this.example.getSomething().subscribe((_url :String)=>
   {
     this._data =_url;
     console.log("Rest1"+this._data);//This log is not showing in console
   });
   }

Answer 1

之所以得到undefined是因为您从未设置过该值。函数setSomething()不会被调用，因此您的变量不会被初始化。

我只是按照相同的方式添加了一个演示。

https://stackblitz.com/edit/angular-hvbzfn

Answer 2

您需要初始化'this.samValue =“ hello”'。

ngOnInit() {
this.example.setSomething(); // for initialisation
   const s= this.example.getSomething().subscribe((_url :String)=>
   {
     this._data =_url;
     console.log("Rest1"+this._data);//This log is not showing in console
   });
   }

  console.log("Rest2"+this._data);This log is showing Rest2 Udefined