How to refresh textfield to be blank after click any button?

The value a field shows is stored in a local variable or rule input. To blank the field you need to modify the underlying value using a saveInto.

If for example, you are saving value of the textfield in variable ri!inputText, then within the buttons' saveInto do a!save(ri!nputText,""). now whenever you click on any such button, ri!inputText will become blank.

do you mean like saveInto:{ri!input,

a!save(),a!save()

}?

i didn't fully understand

Kind of. This is absolute Appian basics and there is plenty of documentation and tutorials. Go there first! The community is for more specific questions once you understand the basics.

but this way may cause ri!inputvalue becomes empty to the database right? I just want it to be saved rightly with value plus the textfield to be blank

I did with saveInto:{ri!input,a!save(),a!save()}, but still not work. By the way, thank you so much for your help, i already finish with that 80 hours tutorial. I see your interface template is really useful, do you have some process model template i can study with? I will be the person in charge of appian in my place at future but none of my team member ever touched appian before.

saveInto:{ri!input,a!save(),a!save()},

This is just plain wrong! a!save() has parameters. What do you expect to happen without passing any values?

Why do you not just lookup the documentation? There are examples!

docs.appian.com/.../fnc_evaluation_save.html

I mean i definitely did with a!save(target:ri!input, value:save!value), but still can't refresh to blank after click buttons, sorry for bother 

Here is a simple code snippet that should help you achieve this functionality. As mentioned by other practitioners, you set the value of your text input to null in the button's saveInto. 

a!localVariables(
  local!text,
  {
    a!textField(
      label: "Input",
      value: local!text,
      saveInto: local!text
    ),
    a!buttonArrayLayout(
      buttons: a!buttonWidget(
        label: "REFRESH INPUT FIELD",
        saveInto: { a!save(local!text, null()) }
      )
    )
  }
)