Angular 2 change detection using observables

Question

I usually manage to find what I'm doing wrong just by looking at existing questions, but nothing helped here.

I am working with a simple Ng2 module that tries to display and update the contents of a NeDB repository.

Remember, I have no problems with the NeDB repository, I confirmed that it updates correctly and loads correctly, so the problems that I have are somewhere else.

I have the following problems:

"asynchronous channel is not working."

---

I have this module.

@NgModule({
    imports: [CommonModule],
    exports: [],
    declarations: [WikiComponent],
    providers: [WikiDbService],
})
export class WikiModule { }

I have this component.

@Component({
    selector: 'wiki',
    templateUrl: './wiki.component.html'
})
export class WikiComponent implements OnInit {

    items: Observable<WikiItem[]>;

    constructor(private _db : WikiDbService) { }

    ngOnInit() {
        this.items = this._db.items;
        this.items.subscribe({
            next: x => console.log("got value", x),
            error: e => console.error("observable error", e),
            complete: () => console.log("done")
        });
    }
}

I have this template.

<p>{{items | async | json}}</p>
<ul>
    <li *ngFor="let item of (items | async)">{{item.name}}</li>
</ul>
<input #newName (keyup)="0">
<button (click)="_db.addByName(newName.value)">ADD</button>

And I have this service.

@Injectable()
export class WikiDbService {
    private sub: BehaviorSubject<WikiItem[]> = new BehaviorSubject<WikiItem[]>([]);
    private db: DataStore;
    public items: Observable<WikiItem[]> = this.sub.asObservable();
    constructor() {
        console.log("BehaviorSubject", this.sub);
        console.log("Observable", this.items);
        this.db = new DataStore(
            { 
                filename: path.join(app.getAppPath(),"wiki.db"),
                autoload: true,
                onload:
                (err)=>{
                    if(!err) {
                        this.db.find<WikiItem>({},
                        (e,docs) => {
                            if(!e) {
                                this.sub.next(docs);
                            }
                        })
                    }
                }
            });
    }

    public add(v: WikiItem) {
        this.db.insert(
            v,
            (e, nDoc) =>
            {
                if(!e) {
                    this.sub.next([...this.sub.getValue(),nDoc]);
                }
            }
        )
    }
    public addByName(str:string) {
        this.add({name: str, _id: undefined});
    }
}

---

When routing to my component with non-empty persistent storage, I get the following console log (corresponding to registration in the component's OnInit method):

got value > [] (wiki.component.ts:20)
got value > [Object, Object, Object, Object] (wiki.component.ts:20)

DOM :

<wiki>
    <p>[]</p>
    <ul>
        <!--template bindings={
          "ng-reflect-ng-for-of": ""
        }-->
    </ul>
    <input>
    <button>ADD</button>
</wiki>

---

, . .

- , ?

---

12/19/16 3:45 pm

ngFor " | " , , , , , , , . .

12/20/16 3.06pm

@olsn, items , , Observable.

. , . .

: ( )

@Component({
    selector: 'wiki',
    templateUrl: './wiki.component.html',
    changeDetection: ChangeDetectionStrategy.OnPush // <=== I've read this might help. It doesn't.
})
export class WikiComponent implements OnInit {

    items: Observable<WikiItem[]> = this._db.items //
        .do(x => console.log("got value", x))      // <== new initialization, with a stream
        .publishReplay().refCount();               //

    constructor(private _db : WikiDbService, private _cd: ChangeDetectorRef) { }

    ngOnInit() {
                      // <=== moved items initialization
    }

    reload() : void {
        this._cd.markForCheck(); // <== added a button to force the change detector to react. Does not do anything.
    }
}

:

<button (click)="reload()">REFRESH</button>

---

@osln .

, sub.next , , , Angular.

Angular NgZone .

@osln.

Answer 1

- ngInit , , , .

@Component({
    selector: 'wiki',
    templateUrl: './wiki.component.html'
})
export class WikiComponent implements OnInit {

    items: Observable<WikiItem[]> = this._db.items
        .do(x => console.log("got value", x)
        // if items is not a Behavior- or ReplaySubject or ReplayObservable, also add the following:
        .publishReplay()
        .refCount(); 

    constructor(private _db : WikiDbService) { }

    ngOnInit() {
        // ..nothing to do here
    }
}

---

, NgZone.run:

DbService: private ngZone: NgZone ( @angular/core), this.sub.next(docs); :

this.ngZone.run(() => this.sub.next(docs));

( )