With ViewBinding in place, wiring up a click listener is direct:

binding.submitButton.setOnClickListener {
    val nameInput = binding.nameEditText.text.toString()
    if (nameInput.isBlank()) {
        binding.errorText.text = "Please enter your name"
    } else {
        binding.greetingText.text = "Hello, $nameInput!"
    }
}

A few things worth noting: .text on an EditText returns an Editable, not a plain String — hence .toString(). isBlank() checks for empty or whitespace-only input, which is usually what you want for form validation rather than just checking isEmpty().

Showing quick feedback with Toast

Toast.makeText(this, "Saved!", Toast.LENGTH_SHORT).show()

Toasts are meant for brief, non-blocking confirmations — not for anything the user must read carefully or respond to.