1 /* 2 * Copyright (C) 2022 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.systemui.util.service; 18 19 import com.android.systemui.util.annotations.WeaklyReferencedCallback; 20 21 /** 22 * The {@link Observer} interface specifies an entity which listeners 23 * can be informed of changes to the source, which will require updating. Note that this deals 24 * with changes to the source itself, not content which will be updated through the interface. 25 */ 26 public interface Observer { 27 /** 28 * Callback for receiving updates from the {@link Observer}. 29 */ 30 @WeaklyReferencedCallback 31 interface Callback { 32 /** 33 * Invoked when the source has changed. 34 */ onSourceChanged()35 void onSourceChanged(); 36 } 37 38 /** 39 * Adds a callback to receive future updates from the {@link Observer}. 40 */ addCallback(Callback callback)41 void addCallback(Callback callback); 42 43 /** 44 * Removes a callback from receiving further updates. 45 * @param callback 46 */ removeCallback(Callback callback)47 void removeCallback(Callback callback); 48 } 49