call async function from angular controller - angular-dart

Question

I want to call an async function from angular form template controller. But if I do so, execution hangs.
Following the html template:
<div class="container">
<form>
<div class="form-group">
<label for="address">Identnummer (Adresse) *</label>
<input type="text" class="form-control" id="address" required placeholder="0x"
[(ngModel)]="model.address"
#address="ngForm"
[ngClass]="setAddressCssValidityClass(address)"
ngControl="address">
</div>
<div class="row">
<div class="col-auto">
<button type="submit" class="btn btn-primary">Submit</button>
</div>
<small class="col text-right">* Required</small>
</div>
</form>
</div>
Here is a simplified version of my controller:
import 'package:angular/angular.dart';
import 'package:angular_forms/angular_forms.dart';
#Component(
selector: 'sCert-validate-form',
templateUrl: 'sCert_validate_form_component.html',
directives: [coreDirectives, formDirectives],
)
class ScertValidateFormComponent {
Map<String, bool> setAddressCssValidityClass(NgControl control) {
var validityClass;
//callCertificateByAddress(control.value);
if(control.value == "test"){
validityClass = 'is-valid';
callCertificateByAddress(control.value);
}
else{
validityClass = 'is-invalid';
}
Map<String, bool> map = {validityClass: true};
return map;
}
Future<bool> callCertificateByAddress(String address) async {
// some code -> also does not work if removed
return true;
}
}
Future<bool> callCertificateByAddress(String address) async has to be async, because I do async lib calls in there. But how can I achieve this in combination with the template?

Answer 1

there is a problem: you bind callback to the input here [ngClass]="setAddressCssValidityClass(address)" angular calls your function [which calls network] on each change detection cycle. and the response from http forces a new change detection which recursively calls http again and again. save the result to some variable and bind it to ngClass instead of a method
ngOnInit() {
this.classes = this.setAddressCssValidityClass(address);
}
....
[ngClass]="classes"

Answer 2

just use async pipe like this
[ngClass]="setAddressCssValidityClass(address) | async"