ios - UITextField validation -

i want know textfield , textview validations.what in app, 1 textview field , 2 textfields.

now wanto done , when clicking button without enter data textfields displays alterview please enter details above fields. how this?plz explain simple example.

i'm not sure understood question, can implement uitextfielddelegate protocol in view controller observe changes text field. can sorts of things that, including on fly validation of text.