ViewTreeSavedStateRegistryOwner.java
/*
* Copyright 2020 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.savedstate;
import android.view.View;
import android.view.ViewParent;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
/**
* Accessors for finding a view tree-local {@link SavedStateRegistryOwner} that allows managing the
* saving state using {@link SavedStateRegistry} for the given view.
*/
public final class ViewTreeSavedStateRegistryOwner {
private ViewTreeSavedStateRegistryOwner() {
// No instances
}
/**
* Set the {@link SavedStateRegistryOwner} responsible for managing the saved state for the
* given {@link View}.
* Calls to {@link #get(View)} from this view or descendants will return {@code owner}.
*
* This is is automatically set for you in the common cases of using fragments or
* ComponentActivity.
*
* <p>This should only be called by constructs such as activities or fragments that manage
* a view tree and their saved state through a {@link SavedStateRegistryOwner}. Callers
* should only set a {@link SavedStateRegistryOwner} that will be <em>stable.</em> The
* associated {@link SavedStateRegistry} should be cleared if the view tree is removed and is
* not guaranteed to later become reattached to a window.</p>
*
* @param view Root view managed by {@link SavedStateRegistryOwner}
* @param owner The {@link SavedStateRegistryOwner} responsible for managing the
* saved state for the given view
*/
public static void set(@NonNull View view, @Nullable SavedStateRegistryOwner owner) {
view.setTag(R.id.view_tree_saved_state_registry_owner, owner);
}
/**
* Retrieve the {@link SavedStateRegistryOwner} responsible for managing the saved state
* for the given {@link View}.
* This may be used to save or restore the state associated with the view.
*
* The returned {@link SavedStateRegistryOwner} is managing all the Views within the Fragment
* or Activity the given {@link View} is added to.
*
* @param view View to fetch a {@link SavedStateRegistryOwner} for
* @return The {@link SavedStateRegistryOwner} responsible for managing the saved state for
* the given view and/or some subset of its ancestors
*/
@Nullable
public static SavedStateRegistryOwner get(@NonNull View view) {
SavedStateRegistryOwner found = (SavedStateRegistryOwner) view.getTag(
R.id.view_tree_saved_state_registry_owner);
if (found != null) return found;
ViewParent parent = view.getParent();
while (found == null && parent instanceof View) {
final View parentView = (View) parent;
found = (SavedStateRegistryOwner) parentView.getTag(
R.id.view_tree_saved_state_registry_owner);
parent = parentView.getParent();
}
return found;
}
}