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      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.annotations.VisibleForTesting;
     20 import com.google.common.base.Optional;
     21 
     22 import javax.annotation.ParametersAreNonnullByDefault;
     23 
     24 /**
     25  * Defines an state interface that any implementation of the interface can be
     26  * operated by {@link StateMachine}.
     27  */
     28 @ParametersAreNonnullByDefault
     29 public interface State {
     30 
     31     public static Optional<State> NO_CHANGE = Optional.absent();
     32 
     33     /**
     34      * Obtains the associated state machine.
     35      *
     36      * @return The associated state machine.
     37      */
     38     public StateMachine getStateMachine();
     39 
     40     /**
     41      * Notifies the state that the state machine is about to transition into
     42      * the state.
     43      *
     44      * @return The next desired state. If it is not NO_CHANGE, the state
     45      * machine will change to the next desired state immediately.
     46      */
     47     public Optional<State> onEnter();
     48 
     49     /**
     50      * Notifies the state that the state machine is about to transition out
     51      * from this state to another state. The state has to release all resources
     52      * it holds at this point.
     53      */
     54     public void onLeave();
     55 
     56     /**
     57      * Obtains the number of registered event handlers in the state.
     58      *
     59      * @return The number of registered event handlers in the state.
     60      */
     61     @VisibleForTesting
     62     public int getEventHandlerCount();
     63 
     64     /**
     65      * Obtains the event handler for a particular type of event.
     66      *
     67      * @param eventClass The type of the event.
     68      * @return An event handler that is able to process the event. Null if the
     69      * state doesn't observe the event.
     70      */
     71     public <T extends Event> EventHandler<T> getEventHandler(Class<T> eventClass);
     72 
     73     /**
     74      * Specifies a handler for a particular type of event.
     75      *
     76      * @param eventClass   The event class.
     77      * @param eventHandler The event handler.
     78      */
     79     public <T extends Event> void setEventHandler(
     80             Class<T> eventClass, EventHandler<T> eventHandler);
     81 
     82     /**
     83      * Removes the handler for a specific type of event.
     84      *
     85      * @param eventClass The event class.
     86      */
     87     public <T extends Event> void removeEventHandler(Class<T> eventClass);
     88 }