Issue
I'm playing around with Kotlin on Android and one thing makes me confused.
When I converted few Fragments from Java to Kotlin I got this:
class XFragment : Fragment() {
private var binding: FragmentXBinding? = null
override fun onCreateView(inflater: LayoutInflater,
container: ViewGroup?, savedInstanceState: Bundle?): View? {
binding = FragmentUhfReadBinding.inflate(inflater, container, false)
return binding!!.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
binding!!.slPower.addOnChangeListener(this)
binding!!.btnClearTagList.setOnClickListener(this)
}
// ...
private fun updateUi(){
binding!!.someTextView.text = getSomeTextViewText()
binding!!.someSlider.value = getSomeSliderValue()
}
}
I can't make binding non-nullable, because it has to be initialized after XFragment class constructor, in onCreateView() or later.
So with this approach it has to be nullable and I have to put !! everywhere.
Is there some way to avoid these !!?
Solution
The official documentation suggests this strategy:
private var _binding: FragmentXBinding? = null
// This property is only valid between onCreateView and
// onDestroyView.
private val binding get() = _binding!!
Ultimately, it becomes just like requireActivity() and requireContext(). You just need to remember not to use it in a callback that might get called outside the view lifecycle.
Note, you can create your view using the super-constructor layout parameter and then bind to the pre-existing view in onViewCreated. Then you might not even need to have it in a property. I rarely need to do anything with it outside onViewCreated() and functions directly called by it:
class XFragment : Fragment(R.layout.fragment_x) {
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
val binding = FragmentXBinding.bind(view)
binding.slPower.addOnChangeListener(this)
binding.btnClearTagList.setOnClickListener(this)
}
}
Answered By - Tenfour04
Answer Checked By - Cary Denson (JavaFixing Admin)
