API Cakupan ViewModel Bagian dari Android Jetpack.

Cakupan adalah kunci untuk menggunakan ViewModel secara efektif. Setiap ViewModel dicakup ke objek yang menerapkan antarmuka ViewModelStoreOwner. Ada beberapa API yang memungkinkan Anda mengelola cakupan ViewModel dengan lebih mudah. Dokumen ini menguraikan beberapa teknik utama yang harus Anda ketahui.

Catatan: Untuk informasi selengkapnya tentang cakupan dan siklus proses ViewModel, lihat Ringkasan ViewModel.

Metode ViewModelProvider.get() memungkinkan Anda mendapatkan instance ViewModel yang dicakupkan ke ViewModelStoreOwner apa pun. Untuk pengguna Kotlin, terdapat berbagai fungsi ekstensi yang tersedia untuk kasus penggunaan paling umum. Semua penerapan fungsi ekstensi Kotlin menggunakan ViewModelProvider API di balik layar.

ViewModel yang dicakupkan ke ViewModelStoreOwner terdekat

Anda dapat menentukan cakupan ViewModel ke Activity, Fragment, atau tujuan grafik Navigation. Fungsi ekstensi viewModels() yang disediakan oleh library Activity, Fragment, dan Navigation, serta fungsi viewModel() di Compose memungkinkan Anda mendapatkan instance ViewModel yang dibatasi ke ViewModelStoreOwner terdekat.

View

import androidx.activity.viewModels

class MyActivity : AppCompatActivity() {
    // ViewModel API available in activity.activity-ktx
    // The ViewModel is scoped to `this` Activity
    val viewModel: MyViewModel by viewModels()
}

import androidx.fragment.app.viewModels

class MyFragment : Fragment() {
    // ViewModel API available in fragment.fragment-ktx
    // The ViewModel is scoped to `this` Fragment
    val viewModel: MyViewModel by viewModels()
}

Penayangan

import androidx.lifecycle.ViewModelProvider;

public class MyActivity extends AppCompatActivity {
    // The ViewModel is scoped to `this` Activity
    MyViewModel viewModel = new ViewModelProvider(this).get(MyViewModel.class);
}

public class MyFragment extends Fragment {
    // The ViewModel is scoped to `this` Fragment
    MyViewModel viewModel = new ViewModelProvider(this).get(MyViewModel.class);
}

Compose

import androidx.lifecycle.viewmodel.compose.viewModel

@Composable
fun MyScreen(
    modifier: Modifier = Modifier,
    // ViewModel API available in lifecycle.lifecycle-viewmodel-compose
    // The ViewModel is scoped to the closest ViewModelStoreOwner provided
    // via the LocalViewModelStoreOwner CompositionLocal. In order of proximity,
    // this could be the destination of a Navigation graph, the host Fragment,
    // or the host Activity.
    viewModel: MyViewModel = viewModel()
) { /* ... */ }

Catatan: Jika Anda menggunakan Hilt dan Jetpack Compose, ganti panggilan viewModel() dengan hiltViewModel() seperti yang dijelaskan dalam dokumentasi Compose + Hilt.

ViewModel yang dicakupkan ke ViewModelStoreOwner apa pun

Fungsi ComponentActivity.viewModels() danFragment.viewModels() di sistem View dan fungsi viewModel() di Compose mengambil parameter ownerProducer opsional yang dapat Anda gunakan untuk menentukan ViewModelStoreOwner tempat instance ViewModel dicakupkan. Contoh berikut menunjukkan cara mendapatkan instance ViewModel yang dicakupkan ke fragmen induk:

View

import androidx.fragment.app.viewModels

class MyFragment : Fragment() {

    // ViewModel API available in fragment.fragment-ktx
    // The ViewModel is scoped to the parent of `this` Fragment
    val viewModel: SharedViewModel by viewModels(
        ownerProducer = { requireParentFragment() }
    )
}

Penayangan

import androidx.lifecycle.ViewModelProvider;

public class MyFragment extends Fragment {

    SharedViewModel viewModel;

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        // The ViewModel is scoped to the parent of `this` Fragment
        viewModel = new ViewModelProvider(requireParentFragment())
            .get(SharedViewModel.class);
    }
}

Compose

import androidx.lifecycle.viewmodel.compose.viewModel

@Composable
fun MyScreen(
    context: Context = LocalContext.current,
    // ViewModel API available in lifecycle.lifecycle-viewmodel-compose
    // The ViewModel is scoped to the parent of the host Fragment
    // where this composable function is called
    viewModel: SharedViewModel = viewModel(
        viewModelStoreOwner = (context as Fragment).requireParentFragment()
    )
) { /* ... */ }

Mendapatkan ViewModel Cakupan Activity dari Fragment adalah kasus penggunaan umum. Kapan melakukannya, gunakan activityViewModels() Fungsi ekstensi View tersedia. Jika tidak menggunakan View dan Kotlin, Anda dapat menggunakan API yang sama seperti di atas dan dengan meneruskan pemilik yang tepat.

View

import androidx.fragment.app.activityViewModels

class MyFragment : Fragment() {

    // ViewModel API available in fragment.fragment-ktx
    // The ViewModel is scoped to the host Activity
    val viewModel: SharedViewModel by activityViewModels()
}

Penayangan

import androidx.lifecycle.ViewModelProvider;

public class MyFragment extends Fragment {

    SharedViewModel viewModel;

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        // The ViewModel is scoped to the host Activity
        viewModel = new ViewModelProvider(requireActivity())
            .get(SharedViewModel.class);
    }
}

Compose

import androidx.lifecycle.viewmodel.compose.viewModel

@Composable
fun MyScreen(
    context: Context = LocalContext.current,
    // ViewModel API available in lifecycle.lifecycle-viewmodel-compose
    // The ViewModel is scoped to the Activity of the host Fragment
    // where this composable function is called
    viewModel: SharedViewModel = viewModel(
        viewModelStoreOwner = (context as Fragment).requireActivity()
    )
) { /* ... */ }

Catatan: Jika Anda menggunakan Hilt dan Jetpack Compose, ganti panggilan viewModel() dengan hiltViewModel() seperti yang dijelaskan dalam Dokumentasi Compose + Hilt.

ViewModel yang dicakupkan ke grafik Navigation

Grafik Navigation juga merupakan pemilik penyimpanan ViewModel. Jika menggunakan Navigation Fragment atau Navigation Compose, Anda bisa mendapatkan instance ViewModel yang dicakupkan ke grafik Navigation dengan navGraphViewModels(graphId) fungsi ekstensi View.

View

import androidx.navigation.navGraphViewModels

class MyFragment : Fragment() {

    // ViewModel API available in navigation.navigation-fragment
    // The ViewModel is scoped to the `nav_graph` Navigation graph
    val viewModel: SharedViewModel by navGraphViewModels(R.id.nav_graph)

    // Equivalent navGraphViewModels code using the viewModels API
    val viewModel: SharedViewModel by viewModels(
        { findNavController().getBackStackEntry(R.id.nav_graph) }
    )
}

Penayangan

import androidx.lifecycle.ViewModelProvider;

public class MyFragment extends Fragment {

    SharedViewModel viewModel;

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        NavController navController = NavHostFragment.findNavController(this);
        NavBackStackEntry backStackEntry = navController.getBackStackEntry(R.id.my_graph);

        // The ViewModel is scoped to the `nav_graph` Navigation graph
        viewModel = new ViewModelProvider(backStackEntry).get(SharedViewModel.class);
    }
}

Compose

import androidx.lifecycle.viewmodel.compose.viewModel

@Composable
fun MyAppNavHost() {
    // ...
    composable("myScreen") { backStackEntry ->
        // Retrieve the NavBackStackEntry of "parentNavigationRoute"
        val parentEntry = remember(backStackEntry) {
            navController.getBackStackEntry("parentNavigationRoute")
        }
        // Get the ViewModel scoped to the `parentNavigationRoute` Nav graph
        val parentViewModel: SharedViewModel = viewModel(parentEntry)
        // ...
    }
}

Jika menggunakan Hilt sebagai tambahan Jetpack Navigation, Anda dapat menggunakan hiltNavGraphViewModels(graphId) API sebagai berikut.

View

import androidx.hilt.navigation.fragment.hiltNavGraphViewModels

class MyFragment : Fragment() {

    // ViewModel API available in hilt.hilt-navigation-fragment
    // The ViewModel is scoped to the `nav_graph` Navigation graph
    // and is provided using the Hilt-generated ViewModel factory
    val viewModel: SharedViewModel by hiltNavGraphViewModels(R.id.nav_graph)
}

Penayangan

import androidx.hilt.navigation.HiltViewModelFactory;
import androidx.lifecycle.ViewModelProvider;

public class MyFragment extends Fragment {

    SharedViewModel viewModel;

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        NavController navController = NavHostFragment.findNavController(this);
        NavBackStackEntry backStackEntry = navController.getBackStackEntry(R.id.my_graph);

        // The ViewModel is scoped to the `nav_graph` Navigation graph
        // and is provided using the Hilt-generated ViewModel factory
        viewModel = new ViewModelProvider(
            backStackEntry,
            HiltViewModelFactory.create(getContext(), backStackEntry)
        ).get(SharedViewModel.class);
    }
}

Compose

import androidx.hilt.navigation.compose.hiltViewModel

@Composable
fun MyAppNavHost() {
    // ...
    composable("myScreen") { backStackEntry ->
        val parentEntry = remember(backStackEntry) {
            navController.getBackStackEntry("parentNavigationRoute")
        }

        // ViewModel API available in hilt.hilt-navigation-compose
        // The ViewModel is scoped to the `parentNavigationRoute` Navigation graph
        // and is provided using the Hilt-generated ViewModel factory
        val parentViewModel: SharedViewModel = hiltViewModel(parentEntry)
        // ...
    }
}