1 /* 2 * Copyright 2018 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 com.android.car.arch.common.switching; 18 19 import androidx.annotation.NonNull; 20 import androidx.annotation.Nullable; 21 import androidx.lifecycle.LiveData; 22 import androidx.lifecycle.MediatorLiveData; 23 24 /** 25 * Provides the implementation of {@link SwitchingLiveData}. This class uses an interface rather 26 * than being exposed directly to ensure that its superclass {@link MediatorLiveData} is not 27 * exposed. The use of MediatorLiveData is an implementation detail. 28 */ 29 class SwitchingLiveDataImpl<T> extends MediatorLiveData<T> implements SwitchingLiveData<T> { 30 private LiveData<? extends T> mCurrentSource; 31 32 @NonNull 33 @Override asLiveData()34 public LiveData<T> asLiveData() { 35 return this; 36 } 37 38 @Nullable 39 @Override getSource()40 public LiveData<? extends T> getSource() { 41 return mCurrentSource; 42 } 43 setSource(@ullable LiveData<? extends T> source)44 public void setSource(@Nullable LiveData<? extends T> source) { 45 if (source == mCurrentSource) { 46 return; 47 } 48 if (mCurrentSource != null) { 49 removeSource(mCurrentSource); 50 } 51 mCurrentSource = source; 52 if (source != null) { 53 addSource(source, this::setValue); 54 } else { 55 setValue(null); 56 } 57 } 58 } 59