Javascript / Angular - html 在渲染代码之前显示

Question

I have a function to get rates from products, so lets say I have one product with two rates. So my product has two rates. Then, when I get those rates I must get the prices attached to my product. So for each rate I have to look for its prices.

The next code below explains this:

this.loadProductInfo = true; // bool to load data in my form

// First of all, I get rates from API
// const rates = this._http....
// Now, for each rate I must search If my product/products have a price:

this.rates.forEach((rate, index, arr) => {
   this._glbGetPricesForProduct.getPrice(params).subscribe(response => {
      if (!arr[index + 1]) {
        this.initForm();
        this.loadProductInfo = false;
      } 
   })
});

The variable loadProductInfo it loads content in my form, so in my html I have:

<form *ngIf="!loadProductInfo"></form>

But form it still give me error: could not find control name.

But if I do this instead, it works correctlly:

setTimeout(() => {
    this.initForm();
    this.loadProductInfo = false;
}, 2000);

So what I want its to say my form to wait until I have all code loaded and then after it, load its contents. But instead it cant find the control because it loads before code. Any help I really appreciate it.

Answer 1

The main mistake I see there is that you are looping over async data which may not be there when your code execute the for each loop (your rates).
I would build an observable with your rates as a source:

...
$rates: Observable<any> = this._http.get(...);
rates.pipe(
    mergeMap((rates) => {
        const priceByRates: Observable<any>[] = rates.map((rate, index, arr) => this._glbGetPricesForProduct.getPrice(params));
        return combineLatest(pricesByRates); // if getPrice complete right away, use forkJoin() instead
    })
).subscribe(res => {
    // No need to check for the last item, all rates have been checked for possible price
    this.initForm();
    this.loadProductInfo = false; 
});
...

This implementation should wait for your api calls to resolve before printing your form.

Answer 2

Since you are hiding the entire form, it may be better to just move the API call into a resolver so that the page does not render until the data is ready.

Here is a minimal StackBlitz showcasing this behavior: https://stackblitz.com/edit/angular-ivy-4beuww

Component

In your component, include an ActivatedRoute parameter via DI.

@Component(/*omitted for brevity*/)
export class MyComponent {
  constructor(private route: ActivatedRoute) {
    // note: 'data' is whatever you label your resolver prop in your routing setup
    route.data.subscribe(resolved => {
      if ("data" in resolved) this.resolveData = resolved["data"];
    });
  }
}

Route Setup

And in your router setup you would have the following:

const routes: Routes = [
  {
    path: 'my-route-path',
    component: MyComponent,
    resolve: {
      data: MyResolver
    }
  }
];

Resolver

Finally, your resolver would make your API call utilizing your service:

@Injectable({providedIn: 'root'})
export class MyResolver() implements Resolve<T> {

  constructor(private service: MyService) {}

  resolve(route: ActivatedRouteSnapshot, state: RouterStateSnapshot): Observable<T> | Promise<T> | any {
    return this.service.myRequest();
  }
}

The final result will be that your view will not be rendered until your data is ready.