NavBackStackEntry.java
/*
* Copyright 2019 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.navigation;
import android.app.Application;
import android.content.Context;
import android.os.Bundle;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.lifecycle.HasDefaultViewModelProviderFactory;
import androidx.lifecycle.Lifecycle;
import androidx.lifecycle.LifecycleOwner;
import androidx.lifecycle.LifecycleRegistry;
import androidx.lifecycle.SavedStateViewModelFactory;
import androidx.lifecycle.ViewModelProvider;
import androidx.lifecycle.ViewModelStore;
import androidx.lifecycle.ViewModelStoreOwner;
import androidx.savedstate.SavedStateRegistry;
import androidx.savedstate.SavedStateRegistryController;
import androidx.savedstate.SavedStateRegistryOwner;
import java.util.UUID;
/**
* Representation of an entry in the back stack of a {@link NavController}. The
* {@link Lifecycle}, {@link ViewModelStore}, and {@link SavedStateRegistry} provided via
* this object are valid for the lifetime of this destination on the back stack: when this
* destination is popped off the back stack, the lifecycle will be destroyed, state
* will no longer be saved, and ViewModels will be cleared.
*/
public final class NavBackStackEntry implements
LifecycleOwner,
ViewModelStoreOwner, HasDefaultViewModelProviderFactory,
SavedStateRegistryOwner {
private final Context mContext;
private final NavDestination mDestination;
private final Bundle mArgs;
private final LifecycleRegistry mLifecycle = new LifecycleRegistry(this);
private final SavedStateRegistryController mSavedStateRegistryController =
SavedStateRegistryController.create(this);
// Internal unique name for this navBackStackEntry;
@NonNull
final UUID mId;
private Lifecycle.State mHostLifecycle = Lifecycle.State.CREATED;
private Lifecycle.State mMaxLifecycle = Lifecycle.State.RESUMED;
private NavControllerViewModel mNavControllerViewModel;
private ViewModelProvider.Factory mDefaultFactory;
NavBackStackEntry(@NonNull Context context,
@NonNull NavDestination destination, @Nullable Bundle args,
@Nullable LifecycleOwner navControllerLifecycleOwner,
@Nullable NavControllerViewModel navControllerViewModel) {
this(context, destination, args,
navControllerLifecycleOwner, navControllerViewModel,
UUID.randomUUID(), null);
}
NavBackStackEntry(@NonNull Context context,
@NonNull NavDestination destination, @Nullable Bundle args,
@Nullable LifecycleOwner navControllerLifecycleOwner,
@Nullable NavControllerViewModel navControllerViewModel,
@NonNull UUID uuid, @Nullable Bundle savedState) {
mContext = context;
mId = uuid;
mDestination = destination;
mArgs = args;
mNavControllerViewModel = navControllerViewModel;
mSavedStateRegistryController.performRestore(savedState);
if (navControllerLifecycleOwner != null) {
mHostLifecycle = navControllerLifecycleOwner.getLifecycle().getCurrentState();
}
updateState();
}
/**
* Gets the destination associated with this entry
* @return The destination that is currently visible to users
*/
@NonNull
public NavDestination getDestination() {
return mDestination;
}
/**
* Gets the arguments used for this entry
* @return The arguments used when this entry was created
*/
@Nullable
public Bundle getArguments() {
return mArgs;
}
/**
* {@inheritDoc}
* <p>
* If the {@link NavHost} has not called {@link NavHostController#setLifecycleOwner}, the
* Lifecycle will be capped at {@link Lifecycle.State#CREATED}.
*/
@NonNull
@Override
public Lifecycle getLifecycle() {
return mLifecycle;
}
void setMaxLifecycle(@NonNull Lifecycle.State maxState) {
mMaxLifecycle = maxState;
updateState();
}
@NonNull
Lifecycle.State getMaxLifecycle() {
return mMaxLifecycle;
}
void handleLifecycleEvent(@NonNull Lifecycle.Event event) {
mHostLifecycle = getStateAfter(event);
updateState();
}
/**
* Update the state to be the lower of the two constraints:
*/
private void updateState() {
if (mHostLifecycle.ordinal() < mMaxLifecycle.ordinal()) {
mLifecycle.setCurrentState(mHostLifecycle);
} else {
mLifecycle.setCurrentState(mMaxLifecycle);
}
}
/**
* {@inheritDoc}
*
* @throws IllegalStateException if called before the {@link NavHost} has called
* {@link NavHostController#setViewModelStore}.
*/
@NonNull
@Override
public ViewModelStore getViewModelStore() {
if (mNavControllerViewModel == null) {
throw new IllegalStateException("You must call setViewModelStore() on your "
+ "NavHostController before accessing "
+ "the ViewModelStore of a navigation graph.");
}
return mNavControllerViewModel.getViewModelStore(mId);
}
@NonNull
@Override
public ViewModelProvider.Factory getDefaultViewModelProviderFactory() {
if (mDefaultFactory == null) {
mDefaultFactory = new SavedStateViewModelFactory(
(Application) mContext.getApplicationContext(),
this,
mArgs);
}
return mDefaultFactory;
}
@NonNull
@Override
public SavedStateRegistry getSavedStateRegistry() {
return mSavedStateRegistryController.getSavedStateRegistry();
}
void saveState(@NonNull Bundle outBundle) {
mSavedStateRegistryController.performSave(outBundle);
}
// Copied from LifecycleRegistry.getStateAfter()
@NonNull
private static Lifecycle.State getStateAfter(@NonNull Lifecycle.Event event) {
switch (event) {
case ON_CREATE:
case ON_STOP:
return Lifecycle.State.CREATED;
case ON_START:
case ON_PAUSE:
return Lifecycle.State.STARTED;
case ON_RESUME:
return Lifecycle.State.RESUMED;
case ON_DESTROY:
return Lifecycle.State.DESTROYED;
case ON_ANY:
break;
}
throw new IllegalArgumentException("Unexpected event value " + event);
}
}