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Android Java 实现事件总线

事件总线(Event Bus)是一种在 Android 开发中常用的组件间通信机制，它可以实现组件间的解耦通信。以下是几种在 Android Java 项目中实现事件总线的方式：

1. 使用第三方库（推荐）

GreenRobot EventBus

添加依赖：

implementation 'org.greenrobot:eventbus:3.3.1'

基本使用：

1. 定义事件类：

public class MessageEvent {public final String message;public MessageEvent(String message) {this.message = message;}
}

2. 注册/注销订阅者（通常在 Activity/Fragment 中）：

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

3. 声明订阅方法：

@Subscribe(threadMode = ThreadMode.MAIN)
public void onMessageEvent(MessageEvent event) {Toast.makeText(this, event.message, Toast.LENGTH_SHORT).show();
}

4. 发布事件：

EventBus.getDefault().post(new MessageEvent("Hello EventBus!"));

2. 自定义简单事件总线

实现代码

import java.lang.ref.WeakReference;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;public class SimpleEventBus {private static volatile SimpleEventBus instance;private final Map<Class<?>, List<Subscriber>> subscribersMap = new HashMap<>();private final Executor executor = Executors.newCachedThreadPool();public static SimpleEventBus getDefault() {if (instance == null) {synchronized (SimpleEventBus.class) {if (instance == null) {instance = new SimpleEventBus();}}}return instance;}public void register(Object subscriber) {Class<?> subscriberClass = subscriber.getClass();Method[] methods = subscriberClass.getDeclaredMethods();for (Method method : methods) {if (method.isAnnotationPresent(Subscribe.class)) {Class<?>[] parameterTypes = method.getParameterTypes();if (parameterTypes.length != 1) {throw new IllegalArgumentException("Subscribe method must have exactly 1 parameter");}Class<?> eventType = parameterTypes[0];Subscriber subscriberWrapper = new Subscriber(new WeakReference<>(subscriber), method);synchronized (this) {List<Subscriber> subscribers = subscribersMap.get(eventType);if (subscribers == null) {subscribers = new ArrayList<>();subscribersMap.put(eventType, subscribers);}subscribers.add(subscriberWrapper);}}}}public void unregister(Object subscriber) {synchronized (this) {for (List<Subscriber> subscribers : subscribersMap.values()) {for (int i = subscribers.size() - 1; i >= 0; i--) {Subscriber subscriberWrapper = subscribers.get(i);Object target = subscriberWrapper.reference.get();if (target == null || target == subscriber) {subscribers.remove(i);}}}}}public void post(Object event) {Class<?> eventClass = event.getClass();List<Subscriber> subscribers;synchronized (this) {subscribers = subscribersMap.get(eventClass);}if (subscribers != null && !subscribers.isEmpty()) {for (Subscriber subscriber : subscribers) {executor.execute(() -> subscriber.invoke(event));}}}private static class Subscriber {private final WeakReference<Object> reference;private final Method method;private final ThreadMode threadMode;Subscriber(WeakReference<Object> reference, Method method) {this.reference = reference;this.method = method;this.method.setAccessible(true);Subscribe annotation = method.getAnnotation(Subscribe.class);this.threadMode = annotation.threadMode();}void invoke(Object event) {Object target = reference.get();if (target == null) return;try {if (threadMode == ThreadMode.MAIN) {new Handler(Looper.getMainLooper()).post(() -> {try {method.invoke(target, event);} catch (Exception e) {e.printStackTrace();}});} else {method.invoke(target, event);}} catch (Exception e) {e.printStackTrace();}}}public @interface Subscribe {ThreadMode threadMode() default ThreadMode.POSTING;}public enum ThreadMode {POSTING, // 与发布者在同一线程MAIN    // 主线程}
}

使用示例

1. 定义事件：

public class CustomEvent {public String data;public CustomEvent(String data) {this.data = data;}
}

2. 注册和订阅：

public class MainActivity extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);SimpleEventBus.getDefault().register(this);}@Overrideprotected void onDestroy() {super.onDestroy();SimpleEventBus.getDefault().unregister(this);}@SimpleEventBus.Subscribe(threadMode = SimpleEventBus.ThreadMode.MAIN)public void onCustomEvent(CustomEvent event) {Toast.makeText(this, event.data, Toast.LENGTH_SHORT).show();}
}

3. 发布事件：

SimpleEventBus.getDefault().post(new CustomEvent("Hello from SimpleEventBus!"));