Hi Alexis,
Greetings from Syncfusion.
We would like to let you know that in Xamarin.Forms iOS, you can use ValueChanged event to achieve your requirement . We have prepared a sample for this.
In Xamarin.iOS, you can use Text Changed event to achieve your requirement and please find the sample for this,
Please check with the above and let us know if you have any concern.
Regards,
Ramya S