input field has to click several times to add numbers

Question

here is my problem, I used ngModelChange function to trigger and event. when i give a number of groups, it gives a number of input fields below that. but that new input fields only allow one integer. if I want to enter another number, I have to click the input field again and again. as an example if I want to input 100. I have to click the same input field 3 times.

here is the html part

    <div class="row">
        <div class="col-md-12">
            <label>Number of Groups </label>
            <input type="number" name="numberofGroups" #numberofGroups="ngModel" [(ngModel)]="StudentCountservice.formData.numberofGroups" (ngModelChange)="onValueChange($event)"class="form-control" required>
        </div>
    </div>
    <div class="row" *ngFor="let grp of groups;let i=index " [attr.data-index]="i" >
        <div class="col-md-12">
            <label>Sizes of Group {{i+1}} </label>
            <input type="number" name="sizeofGroups" #sizeofGroups="ngModel" [(ngModel)]="groups[i]" class="form-control"ng-model-option="{debounce:750}"  required >
        </div>
    </div> 

here is the ts file code part

    onValueChange(newvalue){
    this.groups=[];
    for(var i=0;i<newvalue;i++){
      this.groups[i]=''; 
      }
    }

here is the stackblitz example

https://stackblitz.com/edit/angular-qfadvh

Answer 1

I found this answer (https://github.com/angular/angular/issues/20589). I dropped the following code into your stackblitz and it worked. Give it a try and let me know if you can't get it to work.

Here is my stackblitz fork: https://stackblitz.com/edit/angular-sa8ww6

app.component.ts

// imports and metadata
export class AppComponent  {
  name = 'Angular';
  groups:any =[];

  onValueChange(newvalue){
    this.groups=[];
    for(var i=0;i<newvalue;i++){
      this.groups[i]=''; 
    }
  }

  // Add this function
  trackArray(index, item) {
    return index;
  }

}

app.component.html

Added trackBy: trackArray to your ngFor loop

<div class="row">
  <div class="col-md-12">
    <label>Number of Groups </label>
    <input type="number" name="numberofGroups" #numberofGroups="ngModel" [(ngModel)]="test" (ngModelChange)="onValueChange($event)"class="form-control" required>
  </div>
</div>

<!-- add the trackBy: trackArray to this ngFor -->
<div class="row" *ngFor="let grp of groups;let i=index; trackBy: trackArray " [attr.data-index]="i" >
  <div class="col-md-12">
    <label>Sizes of Group {{i+1}} </label>
    <input type="number" name="sizeofGroups" #sizeofGroups="ngModel" [(ngModel)]="groups[i]" class="form-control"ngModelOptions="{updateOn: 'blur'}"  required >
  </div>
</div>