You can call this method using the "change" event of the input element, so when the variable (in the case of the input content) is changed, the method is called. Ex.:
<input type="text" [(ngModel)]="suaVariavel" (change)="seuMetodo($event)" />
Remembering that if you want to change the value of this variable through the code, the line above will generate an infinite loop, because both ngModel and its method will be trying to change the same variable, if this is the case, better use the alternative below:
<input type="text" [ngModel]="suaVariavel" (ngModelChange)="seuMetodo($event)" />
Note that when using (change), the method call will only occur when the field loses focus, but the method will be called with the correct field information.
What code do you have to show us?
– fsi