Angular 2+ wait for subscribe to finish to update/access variable

问题

Hello I am having an issue with my variables being undefined. I am certain this is because the observable hasnt finished. Here is the part of my code in my .ts file that is causing the issue: (I'm placing the minimum code required to understand the issue, if I need to provide more code and context let me know. Also myFunction gets called from a click event in the html.)

export class myClass {
  myVariable: any;

  myFunction() {
    this.myService.getApi().subscribe(data => {
      this.myVariable = data;
    });

    console.log(myVariable) --> undefined
  }
}

So this piece of code calls a function in my service that returns some data from an api. The issue is that when I try to access the variable myVariable right outside of the subscribe function it returns undefined. Im sure this is because the subscribe hasnt finished before I try to access myVariable

Is there a way to wait for the subscribe to finish before I try to access myVariable?

Thanks!

回答1:

why not create a separate function and call it inside the subscription.

export class myClass {
  myVariable: any;

  myFunction() {
    this.myService.getApi().subscribe(data => {
      this.myVariable = data;
      this.update()
    });

    this.update()
  }

  update(){
    console.log(this.myVariable);
  }
}

回答2:

As you know subscriptions are executed when server return data but the out side of subscription code executed synchronously. That is why console.log outside of it executed. The above answer can do your job but you can also use .map and return observable as shown below.

let say you are calling it from s service

export class myClass {
  myVariable: any;

  // calling and subscribing the method.
  callingFunction() {

    // the console log will be executed when there are data back from server
    this.myClass.MyFunction().subscribe(data => {
      console.log(data);
    });
  }
}


export class myClass {
  myVariable: any;

  // this will return an observable as we did not subscribe rather used .map method
  myFunction() {
    // use .pipe in case of rxjs 6 
    return this.myService.getApi().map(data => {
      this.myVariable = data;
      this.update()
    });
  }

}

来源：https://stackoverflow.com/questions/50951779/angular-2-wait-for-subscribe-to-finish-to-update-access-variable

标签

angular

observable