Fragment간 ViewModel로 데이터 전달

1. 프래그먼트 간 데이터 공유

Activity에 포함된 둘 이상의 프래그먼트는 ViewModel을 통해서 데이터 공유가 가능합니다.

위 그림과 같이 Fragment들은 각자의 ViewModel를 가질 수도 있고 Activity의 ViewModel을 공유해서 사용할 수도 있는 것 입니다.

2. 코드 적용하기

1. Fragment1

class Fragment1 : Fragment() {

    private val sharedViewModel: SharedViewModel by activityViewModels()
    private lateinit var binding: Fragment1Binding

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {

        binding = Fragment1Binding.inflate(inflater, container, false)

        binding.buttonFragment1.setOnClickListener {
            sharedViewModel.updateText(binding.editTextFromFragment1.text as Editable)
        }

        sharedViewModel.getData().observe(viewLifecycleOwner, Observer {
            binding.editTextFromFragment1.text = it as Editable
        })

        return binding.root
    }
}

sharedViewModel.getData().observe()를 통해서 ViewModel에 선언된 MutableLiveData의 data 값이 변하는지 관찰합니다. 이러한 옵저빙을 통해서 데이터 변환이 감지되면 text값을 갱신해 줍니다.

2. Fragment2

class Fragment2 : Fragment() {

    private lateinit var binding: Fragment2Binding
    private val sharedViewModel: SharedViewModel by activityViewModels()

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {

        binding = Fragment2Binding.inflate(inflater, container, false)

        binding.buttonFragment2.setOnClickListener {
            sharedViewModel.updateText(binding.editTextFromFragment2.text as Editable)
        }

        sharedViewModel.getData().observe(viewLifecycleOwner, Observer {
            binding.editTextFromFragment2.text = it as Editable
        })
        return binding.root
    }
}

3. SharedViewModel

class SharedViewModel : ViewModel() {

    private var inputText: MutableLiveData<CharSequence> = MutableLiveData()

    fun getData(): MutableLiveData<CharSequence> = inputText

    fun updateText(input: CharSequence) {
        inputText.value = input
    }
}

4. MainActivity

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val fragmentTransaction: FragmentTransaction = supportFragmentManager.beginTransaction()

        fragmentTransaction.apply {
            add(R.id.fragment_1_holder, Fragment1())
            add(R.id.fragment_2_holder, Fragment2())
            commit()
        }
    }
}

3. reference

https://www.geeksforgeeks.org/fragment-to-fragment-communication-in-android-using-shared-viewmodel/