手写EventBus

前言

EventBus是一种用于Android的事件发布-订阅总线，由GreenRobot开发，Gihub地址是：EventBus。它简化了应用程序内各个组件之间进行通信的复杂度，尤其是碎片之间进行通信的问题，可以避免由于使用广播通信而带来的诸多不便。

像这样的框架如何进行实现呢，我们就手写一个。

工程目录结构

一，定义枚举类

枚举类，用于线程切换。

public enum ThreadMode {
    MAIN,BACKGROUND
}

二，注解类

注解@Target：用于描述注解的使用范围，ElementType.METHOD，用于描述方法。
注解@Retention：表示需要在什么级别保存该注释信息，用于描述注解的生命周期。RetentionPolicy.RUNTIME，代表在运行时有效。

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Subscribe {
 ThreadMode threadMode() default ThreadMode.MAIN;
}

三，实体类

用于存放方法和类

public class SubscribeMethod {
    //回调方法
    private Method mMethod;
    //线程模式
    private ThreadMode mThreadMode;
    //方法中的参数
    private Class type;

    public SubscribeMethod(Method mMethod, ThreadMode mThreadMode, Class type) {
        this.mMethod = mMethod;
        this.mThreadMode = mThreadMode;
        this.type = type;
    }

    public Method getmMethod() {
        return mMethod;
    }

    public void setmMethod(Method mMethod) {
        this.mMethod = mMethod;
    }

    public ThreadMode getmThreadMode() {
        return mThreadMode;
    }

    public void setmThreadMode(ThreadMode mThreadMode) {
        this.mThreadMode = mThreadMode;
    }

    public Class getType() {
        return type;
    }

    public void setType(Class type) {
        this.type = type;
    }
}

发送消息实体类

public class EventBean {
    private int state;
    private String message;
    public EventBean(int state, String message) {
        this.state = state;
        this.message = message;
    }
    public int getState() {
        return state;
    }

    public void setState(int state) {
        this.state = state;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    @Override
    public String toString() {
        return "EventBean{" +
                "state=" + state +
                ", message='" + message + '\'' +
                '}';
    }
}

四，消息发送和接收实现类

public class EventBus {
    private Map> cacheMap;
    private Handler mHander;
    private static volatile EventBus instance;

    private EventBus() {
        cacheMap = new HashMap<>();
        mHander=new Handler();
    }

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

    public void register(Object object) {
        List list = cacheMap.get(object);
        if (list == null) {
            list = findSubscribeMethods(object);
            cacheMap.put(object, list);
        }
    }

    private List findSubscribeMethods(Object object) {
        List list = new ArrayList<>();
        Class clazz = object.getClass();
        Method[] methods = clazz.getDeclaredMethods();
        while (clazz != null) {
            //找父类的时候，需要先判断是否是系统级别父类
            String name = clazz.getName();
            if (name.startsWith("java.") || name.startsWith("javax.")
                    || name.startsWith("android.")) {
                break;
            }
            for (Method method : methods) {
                //找到带有Subcribe注解的方法
                Subscribe subscribe = method.getAnnotation(Subscribe.class);
                if (subscribe == null) {
                    continue;
                }
                Class[] types = method.getParameterTypes();
                if (types.length != 1) {
                    Log.e("EventBus", "findSubscribeMethods: 错误");
                }
                ThreadMode threadMode = subscribe.threadMode();
                SubscribeMethod subscribeMethod = new SubscribeMethod(method, threadMode, types[0]);
                list.add(subscribeMethod);
            }
            clazz = clazz.getSuperclass();
        }

        return list;
    }

    public void post(final Object type) {
        //直接循环map里的方法
        Set