将离子选择选项传递给功能-离子4

我有这个Ionic版本4代码，该代码只是试图获取所选值并将其传递给组件中的函数:

I have this Ionic version 4 code that is simply trying to take a the selected value and pass it to a function in it's component:

<ion-item>
<ion-label>Convert Currency</ion-label>
<ion-select [(ngModel)]="currency">
<ion-select-option *ngFor="let c of currencyData" [value] = "c" >{{c.text}}</ion-select-option>
</ion-select>

我尝试了onChange，但显然不在版本4中.

I tried onChange but that is apparently not in version 4.