Fragments trong Android

1. Giới thiệu

Fragment là một phần UI có thể tái sử dụng, có lifecycle riêng, nằm trong Activity.

Lưu ý: Với Jetpack Compose, việc sử dụng Fragment giảm đáng kể. Tuy nhiên, hiểu Fragment vẫn quan trọng cho legacy projects và một số use cases.

2. Khi nào dùng Fragment?

Nên dùng Fragment khi:

Làm việc với XML Views (legacy)
Multi-pane layouts (tablet)
Bottom Navigation với Fragment
Integration với third-party libraries yêu cầu Fragment

Với Compose:

Ưu tiên Navigation Compose
Không cần Fragment cho hầu hết use cases
Có thể dùng Fragment để host Compose UI nếu cần

3. Tạo Fragment cơ bản


class HomeFragment : Fragment() {
    
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        return ComposeView(requireContext()).apply {
            setContent {
                HomeScreen()
            }
        }
    }
}

4. Fragment Lifecycle


Fragment Added
      │
      ▼
onAttach() → onCreate() → onCreateView() → onViewCreated()
      │
      ▼
onStart() → onResume()
      │
      ▼ (User interacts)
      │
onPause() → onStop()
      │
      ▼
onDestroyView() → onDestroy() → onDetach()


class MyFragment : Fragment() {
    
    override fun onAttach(context: Context) {
        super.onAttach(context)
        Log.d(TAG, "onAttach")
    }
    
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        Log.d(TAG, "onCreate")
    }
    
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        Log.d(TAG, "onCreateView")
        return inflater.inflate(R.layout.fragment_my, container, false)
    }
    
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        Log.d(TAG, "onViewCreated")
    }
    
    override fun onDestroyView() {
        super.onDestroyView()
        Log.d(TAG, "onDestroyView")
    }
    
    override fun onDestroy() {
        super.onDestroy()
        Log.d(TAG, "onDestroy")
    }
}

5. Fragment với Arguments


class DetailFragment : Fragment() {
    
    companion object {
        private const val ARG_ID = "id"
        
        fun newInstance(id: Int): DetailFragment {
            return DetailFragment().apply {
                arguments = Bundle().apply {
                    putInt(ARG_ID, id)
                }
            }
        }
    }
    
    private val itemId: Int by lazy {
        arguments?.getInt(ARG_ID) ?: 0
    }
    
    override fun onCreateView(...): View {
        return ComposeView(requireContext()).apply {
            setContent {
                DetailScreen(itemId)
            }
        }
    }
}

6. FragmentManager


// Trong Activity
supportFragmentManager.commit {
    replace(R.id.fragment_container, HomeFragment())
    addToBackStack(null)
}
 
// Trong Fragment
parentFragmentManager.commit {
    replace(R.id.fragment_container, DetailFragment.newInstance(123))
    addToBackStack(null)
}

7. Fragment với ViewModel


class HomeFragment : Fragment() {
    
    // Scoped to Fragment
    private val viewModel: HomeViewModel by viewModels()
    
    // Shared with Activity
    private val sharedViewModel: SharedViewModel by activityViewModels()
    
    override fun onCreateView(...): View {
        return ComposeView(requireContext()).apply {
            setContent {
                val state by viewModel.uiState.collectAsState()
                HomeScreen(state)
            }
        }
    }
}

8. Fragment Communication

Shared ViewModel (Recommended)


// SharedViewModel
class SharedViewModel : ViewModel() {
    private val _selectedItem = MutableLiveData<Item>()
    val selectedItem: LiveData<Item> = _selectedItem
    
    fun selectItem(item: Item) {
        _selectedItem.value = item
    }
}
 
// Fragment A
sharedViewModel.selectItem(item)
 
// Fragment B
sharedViewModel.selectedItem.observe(viewLifecycleOwner) { item ->
    // Handle selected item
}

Fragment Result API


// Fragment A (listener)
setFragmentResultListener("requestKey") { key, bundle ->
    val result = bundle.getString("resultKey")
}
 
// Fragment B (sender)
setFragmentResult("requestKey", bundleOf("resultKey" to "Result"))


<!-- activity_main.xml -->
<androidx.fragment.app.FragmentContainerView
    android:id="@+id/nav_host_fragment"
    android:name="androidx.navigation.fragment.NavHostFragment"
    app:navGraph="@navigation/nav_graph"
    app:defaultNavHost="true" />
 
<com.google.android.material.bottomnavigation.BottomNavigationView
    android:id="@+id/bottom_nav"
    app:menu="@menu/bottom_nav_menu" />


class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        
        val navHostFragment = supportFragmentManager
            .findFragmentById(R.id.nav_host_fragment) as NavHostFragment
        val navController = navHostFragment.navController
        
        findViewById<BottomNavigationView>(R.id.bottom_nav)
            .setupWithNavController(navController)
    }
}

10. Compose trong Fragment


class ComposeFragment : Fragment() {
    
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        return ComposeView(requireContext()).apply {
            setViewCompositionStrategy(
                ViewCompositionStrategy.DisposeOnViewTreeLifecycleDestroyed
            )
            setContent {
                MaterialTheme {
                    MyComposeScreen()
                }
            }
        }
    }
}

📝 Tóm tắt

Aspect	Fragment	Compose
UI	XML Views	Composables
Lifecycle	Complex	Simplified
Navigation	FragmentManager	NavController
State	ViewModel + LiveData	State + ViewModel
Reusability	Fragment.newInstance()	@Composable functions

Khuyến nghị: Với dự án mới, ưu tiên Jetpack Compose và Navigation Compose. Chỉ dùng Fragment khi thực sự cần thiết.

Fragments trong Android

1. Giới thiệu

2. Khi nào dùng Fragment?

Nên dùng Fragment khi:

Với Compose:

3. Tạo Fragment cơ bản

4. Fragment Lifecycle

5. Fragment với Arguments

6. FragmentManager

7. Fragment với ViewModel

8. Fragment Communication

Shared ViewModel (Recommended)

Fragment Result API

9. Bottom Navigation với Fragments

10. Compose trong Fragment

📝 Tóm tắt