ionic2 how to get checkbox status

here is the context:

I have a list of users.

I also have a list of items and each item holds an Array of users.

The items list is displayed like that:

  <ion-list>
    <ion-item *ngFor="let item of items">
      <ion-checkbox item-left [checked]="isChecked(item)" *ngIf="selected_user;"></ion-checkbox>
      <ion-label>
        
        <br>
        <ion-badge *ngFor="let user of item.users"></ion-badge>
      </ion-label>
    </ion-item>
  </ion-list>

Basically the checkboxes are revealed when a user is selected somewhere else.

What I am trying to do is to modify for each item its users array according to the status of the checkbox.

For instance, if item_a.users contain user1 and selected_user is user1 its checkbox revealed as checked (I have that already) but now if item_b and item_c will be checked I want to add user1 to their users array and if item_a is unchecked I want to remove user1 from its users array.

Is there any event to catch here? Is there a way to get all the status together in some data structure or I have to handle it individually for each item?

Thanks.