Ionic 3 select option checkboxes deselect event

I have strange requirement, I am having 4 options from dropdown out of 4 I have to allow select only 3 in ionic 3 dropdown, I have been trying with many ways but nothing is working. Could anybody help me out this please.

<ion-select okText="{{ okText }}" cancelText="{{ cancelText }}" (click)=“rioNotificationsClicked()” (ionChange)=“setRoiTypeValue(roi)”
[(ngModel)]=“roi” multiple=“true” class=“dropdownIonNotiSelect notificationDropdownIonSelect”>
<ion-option (ionSelect)=“dataChanged(roi)” [value]=“roi” *ngFor=“let roi of roiTypeData;”>{{roi.flooresenseCodeName}}

ionSelect is firing when we select the checkbox but its not firing when we de-select the checkbox and ionChange event is not firing on click of options/checkbox, its firing when when we click on Ok button. Please anybody help me, I am struck with from morning.