How can you ensure the preservation of user interface state within a fragment in a mobile app?

To preserve the user interface state in an Android fragment, the onSaveInstanceState(Bundle outState) method is usually used. In this method, you can save the necessary data into a Bundle, which is then restored in onViewCreated or onActivityCreated when the fragment is recreated.

Example:

override fun onSaveInstanceState(outState: Bundle) {
    super.onSaveInstanceState(outState)
    outState.putString("key_text", editText.text.toString())
}

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    if (savedInstanceState != null) {
        val savedText = savedInstanceState.getString("key_text")
        editText.setText(savedText)
    }
}

You can also use ViewModel to store the state, which allows you to save data during configuration changes without needing to save it in a Bundle.