1 /* 2 * Copyright (C) 2015 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.camera.captureintent.stateful; 18 19 import com.google.common.base.Optional; 20 21 /** 22 * Defines an event handler interface that any implementation of this interface 23 * can be used by {@link StateMachine} to handle a particular type of event 24 * which extends {@link Event}. 25 * 26 * @param <T> The particular type of event. 27 */ 28 public interface EventHandler<T extends Event> { 29 30 /** 31 * Process a single event. 32 * 33 * @param event The event to be processed. 34 * @return The next desired state. If it is not NO_CHANGE, the state 35 * machine will change to the next desired state. 36 */ processEvent(T event)37 public Optional<State> processEvent(T event); 38 }