A the function that triggers always when displaying a component in an ionic2

What would be the function that triggers always when displaying a component in an ionic2 app.

E.g As I noticed constructor function in a component triggers only when the component is initialize for the first time or when you do a push from a different page.

But constructor will not trigger when clicking the back button or switch between tabs

Is there any method that will call every time when the component is displayed on the screen ?

Thanks in advance

cheers

Sam