如何从内部具有Observable订阅的angular函数返回值

Question

I want to write a generic method in my angular class to return a value from an observable and set a number of class properties. My code resembles below

export class SomeServiceClass implements OnInit {

someProperty1: someObject;
someProperty2: someObject;
somePropertyN: someObject;

ngOnInit() {
     this.someProperty1 = getValueFromObservableGenericMethod("value1")
     this.someProperty2 = getValueFromObservableGenericMethod("value2")
     this.somePropertyN = getValueFromObservableGenericMethod("valueN")

    console.log(someProperty1); // undefined
    console.log(someProperty2); // undefined
    console.log(someProperty3); // undefined
}


getValueFromObservableGenericMethod(someIncomingString: string): someObject {

    let localVar: someObject;

    this.anotherServiceClass.subscribe(
        data => {
            localVar = data;
        },
        () => {
            return localVar;;
            console.log(localVar);
        }
    )

    return localVar;

}
}

My class properties are all undefined after the method call. The localVar is available though on complete function. Any ideas how can we possibly return values from such a function call?

Answer 1

Working on your example, the following modifications should be made:

export class SomeServiceClass implements OnInit {

    someProperty1: someObject;
    someProperty2: someObject;
    somePropertyN: someObject;

    ngOnInit() {
        getValueFromObservableGenericMethod("value1").subscribe(result => {
            this.someProperty1 = result;
            console.log(someProperty1); // not undefined anymore            
        }
}


getValueFromObservableGenericMethod(someIncomingString: string): Observable<someObject> 
{

    let localVar: someObject;
    // notice that I changed subscribe with map
    return this.anotherServiceClass.map(
        data => {
            localVar = data;
        },
        () => {
            return localVar;;
            console.log(localVar);
        }
    )
}
}

Now to get to explanations: A property cannot take an Observable value, that's why you will have to subscribe to the function that you want to return the desired value. if you have anymore questions just ask and I will try my best to explain.