How to detect backspace/clear button in Entry control when it is empty

I am using Xamarin Forms with both iOS and Android. I have a form which has 4 Entry controls for a user to enter postcode. I am using TextChanged event to detect user input and automatically move focus to the next control. This part works fine, i.e. as user types a digit focus automatically jumps to the next entry. However, I need to achieve the opposite, user should be able to tap backspace/clear/delete button and focus should move to the previous control. The problem is that TextChanged is not triggered when entry control is empty. How can I achieve this? Is there a custom renderer I can create for each platform to capture text input? Maybe there is a way to use 1 entry instead but I need to make it look like distinct 4 boxes.