1/*
2 * Copyright (C) 2017 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package androidx.lifecycle;
18
19import java.util.HashMap;
20
21/**
22 * Class to store {@code ViewModels}.
23 * <p>
24 * An instance of {@code ViewModelStore} must be retained through configuration changes:
25 * if an owner of this {@code ViewModelStore} is destroyed and recreated due to configuration
26 * changes, new instance of an owner should still have the same old instance of
27 * {@code ViewModelStore}.
28 * <p>
29 * If an owner of this {@code ViewModelStore} is destroyed and is not going to be recreated,
30 * then it should call {@link #clear()} on this {@code ViewModelStore}, so {@code ViewModels} would
31 * be notified that they are no longer used.
32 * <p>
33 * Use {@link ViewModelStoreOwner#getViewModelStore()} to retrieve a {@code ViewModelStore} for
34 * activities and fragments.
35 */
36public class ViewModelStore {
37
38    private final HashMap<String, ViewModel> mMap = new HashMap<>();
39
40    final void put(String key, ViewModel viewModel) {
41        ViewModel oldViewModel = mMap.put(key, viewModel);
42        if (oldViewModel != null) {
43            oldViewModel.onCleared();
44        }
45    }
46
47    final ViewModel get(String key) {
48        return mMap.get(key);
49    }
50
51    /**
52     *  Clears internal storage and notifies ViewModels that they are no longer used.
53     */
54    public final void clear() {
55        for (ViewModel vm : mMap.values()) {
56            vm.onCleared();
57        }
58        mMap.clear();
59    }
60}
61