ViewTreeViewModelStoreOwner.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.lifecycle;
import android.view.View;
import android.view.ViewParent;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.lifecycle.viewmodel.R;
/**
* Accessors for finding a view tree-local {@link ViewModelStoreOwner} that allows access to a
* {@link ViewModelStore} for the given view.
*/
public class ViewTreeViewModelStoreOwner {
private ViewTreeViewModelStoreOwner() {
// No instances
}
/**
* Set the {@link ViewModelStoreOwner} associated with the given {@link View}.
* Calls to {@link #get(View)} from this view or descendants will return
* {@code viewModelStoreOwner}.
*
* <p>This should only be called by constructs such as activities or fragments that manage
* a view tree and retain state through a {@link ViewModelStoreOwner}. Callers
* should only set a {@link ViewModelStoreOwner} that will be <em>stable.</em> The associated
* {@link ViewModelStore} 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 associated with the viewModelStoreOwner
* @param viewModelStoreOwner ViewModelStoreOwner associated with the given view
*/
public static void set(@NonNull View view, @Nullable ViewModelStoreOwner viewModelStoreOwner) {
view.setTag(R.id.view_tree_view_model_store_owner, viewModelStoreOwner);
}
/**
* Retrieve the {@link ViewModelStoreOwner} associated with the given {@link View}.
* This may be used to retain state associated with this view across configuration changes.
*
* @param view View to fetch a {@link ViewModelStoreOwner} for
* @return The {@link ViewModelStoreOwner} associated with this view and/or some subset
* of its ancestors
*/
@Nullable
public static ViewModelStoreOwner get(@NonNull View view) {
ViewModelStoreOwner found = (ViewModelStoreOwner) view.getTag(
R.id.view_tree_view_model_store_owner);
if (found != null) return found;
ViewParent parent = view.getParent();
while (found == null && parent instanceof View) {
final View parentView = (View) parent;
found = (ViewModelStoreOwner) parentView.getTag(R.id.view_tree_view_model_store_owner);
parent = parentView.getParent();
}
return found;
}
}