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 
17 package androidx.lifecycle;
18 
19 import 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  */
36 public class ViewModelStore {
37 
38     private final HashMap<String, ViewModel> mMap = new HashMap<>();
39 
put(String key, ViewModel viewModel)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 
get(String key)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      */
clear()54     public final void clear() {
55         for (ViewModel vm : mMap.values()) {
56             vm.onCleared();
57         }
58         mMap.clear();
59     }
60 }
61