RxJava替代EventBus：RxBus

由于最近工程中依賴于RxAndroid與RxJava，因此以RxJava模式實現EventBus相同的API，移除重復功能的依賴，達到精簡工程的目的。

第一步：構造單例

1. 在EventBus中

   EventBus.getDefault();

2. 構造RxBus相同的API

   public class RxBus {    
      private static volatile RxBus instance;    
      private RxBus() {}    
      public static RxBus getDefault() {        
         if (instance == null) {           
             synchronized (RxBus.class) {                
                 if (instance == null) {                    
                     instance = new RxBus();                
                 }            
              }        
         }        
         return instance;    
      }

3. 在RxBus中

   RxBus.getDefault();

第二步：事件注解

1. 在EventBus中

   @Subscribe
   public void onMessageEvent(MessageEvent event) {/* Do something */};

2. 構造RxBus相同的API

   public class RxBus { 
   
      //省略第一步...
   
      @Target(ElementType.METHOD)
      @Retention(RetentionPolicy.RUNTIME)
      public @interface Subscribe {}
   }

3. 在RxBus中

   @RxBus.Subscribe
   public void onMessageEvent(MessageEvent event) {/* Do something */};

第三步：訂閱事件

1. 在EventBus中

   @Override
   public void onStart() { 
      super.onStart(); 
      EventBus.getDefault().register(this);
   }

2. 構造RxBus相同的API

   public class RxBus { 
   
      //省略第一步...
   
      private final Subject<Object, Object> bus = new SerializedSubject<>(PublishSubject.create());
      private final ArrayMap<String, List<Subscription>> subscriptionArray = new ArrayMap<>();
   
      public void register(final Object observable) {    
          boolean isRegisterSuccess = false;    
          final String subscriptionKey = observable.getClass().getName();
          //反射獲取方法列表  
          Method[] methods = observable.getClass().getMethods();    
          for (Method method : methods) {    
              //如果方法不存在Subscribe注解則不做處理
              if (!method.isAnnotationPresent(Subscribe.class)) continue;        
              final Method subscriptionMethod = method;
              //獲取方法參數類型，即：MessageEvent.class
              Class<?> key = method.getParameterTypes()[0];
              //訂閱MessageEvent.class類型實例，ofType作用已filter相近
              Subscription subscription = bus.ofType(key).subscribe(new Action1<Object>() {
                  @Override            
                  public void call(Object value) {
                      try {
                          //反射賦值，即傳遞事件值
                          subscriptionMethod.setAccessible(true);
                          subscriptionMethod.invoke(observable, value);
                      } catch (IllegalAccessException | InvocationTargetException e) { 
                          throw new RuntimeException(subscriptionKey + " isn't allowed to register!");
                      }
                  }
              });
              //存儲訂閱實例列表，用于后續解除注冊
              List<Subscription> subscriptions;
              if (subscriptionArray.containsKey(subscriptionKey)) {
                 subscriptions = subscriptionArray.get(subscriptionKey);
              } else {
                 subscriptions = new ArrayList<>();
              }
              subscriptions.add(subscription);
              subscriptionArray.put(subscriptionKey, subscriptions); 
              isRegisterSuccess = true;
          }
          //如果注冊的類中不存在Subscribe注解方法，則拋出異常提醒
          if (!isRegisterSuccess) 
              throw new RuntimeException(subscriptionKey + " has no any RxBuxSubscribe Event!");
      }
   
      //省略第二步...
   }

3. 在RxBus中

   @Override
   public void onStart() { 
      super.onStart(); 
      RxBus.getDefault().register(this);
   }

取消訂閱

1. 在EventBus中

   @Override
   public void onStop() { 
      super.onStop(); 
      EventBus.getDefault().unregister(this);
   }

2. 構造RxBus相同的API

   public class RxBus { 
   
      //省略第一步...
      //省略第三步...
   
      public void unregister(Object observable) {    
          String subscriptionKey = observable.getClass().getName();
          if (!subscriptionArray.containsKey(subscriptionKey)) return;
          List<Subscription> subscriptions = subscriptionArray.get(subscriptionKey);
          for (Subscription subscription : subscriptions) {
              //如果已訂閱，則取消訂閱
              if (!subscription.isUnsubscribed()) subscription.unsubscribe();
          }
          subscriptionArray.remove(subscriptionKey);
      }      
   
      //省略第二步...
   }

3. 在RxBus中

   @Override
   public void onStop() { 
      super.onStop(); 
      RxBus.getDefault().unregister(this);
   }

發送事件

1. 在EventBus中

   EventBus.getDefault().post(new MessageEvent());

2. 構造RxBus相同的API

   public class RxBus { 
   
      //省略第一步...
      //省略第三步...
      //省略第四步...     
   
      public void post (Object event) { 
          bus.onNext(event);
      }
   
      //省略第二步...
   }

3. 在RxBus中

   RxBus.getDefault().post(new MessageEvent());

關于ThreadMode

在訂閱時根據需要使用RxJava的Schedulers即可。

來自：http://www.jianshu.com/p/4eb68b206fe0