@interface Subscribe分析

前面參考的代碼，存放在（use_little_demo中的 eventbus3test）
https://github.com/2954722256/use_little_demo

我們通過eventbus3的注解

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

    /**
     * If true, delivers the most recent sticky event (posted with
     * {@link EventBus#postSticky(Object)}) to this subscriber (if event available).
     */
    boolean sticky() default false;

    /** Subscriber priority to influence the order of event delivery.
     * Within the same delivery thread ({@link ThreadMode}), higher priority subscribers will receive events before
     * others with a lower priority. The default priority is 0. Note: the priority does *NOT* affect the order of
     * delivery among subscribers with different {@link ThreadMode}s! */
    int priority() default 0;
}

我們可以看見，和我們自己例子類似的結構
這里多了個@Documentd， 這個也提到過，文檔相關的，我們可以忽略

簡單扯淡
通過

• @Retention(RetentionPolicy.RUNTIME)
• @Target({ElementType.METHOD})

我們可以知道，是放在方法上面使用的
（我們上一篇是放在類上面使用的，和這個不同的是，只是放在方法前面使用）
也就是上圖使用的形式

這里接口，有3個方法
我們可以發現，對應的一些配置，例如

其實，都是通過注解傳入值的
（上一篇，我們也有對應的傳值例子，具體可以參考）

簡單復習

第一篇，我們提到過，有4中模式
也就是這里配置的threadMode()返回類型ThreadMode

我們來看一下ThreadMode類
ThreadMode

/**
 * Each event handler method has a thread mode, which determines in which thread the method is to be called by EventBus.
 * EventBus takes care of threading independently from the posting thread.
 * 
 * @see EventBus#register(Object)
 * @author Markus
 */
public enum ThreadMode {
    /**
     * Subscriber will be called in the same thread, which is posting the event. This is the default. Event delivery
     * implies the least overhead because it avoids thread switching completely. Thus this is the recommended mode for
     * simple tasks that are known to complete is a very short time without requiring the main thread. Event handlers
     * using this mode must return quickly to avoid blocking the posting thread, which may be the main thread.
     */
    POSTING,

    /**
     * Subscriber will be called in Android's main thread (sometimes referred to as UI thread). If the posting thread is
     * the main thread, event handler methods will be called directly. Event handlers using this mode must return
     * quickly to avoid blocking the main thread.
     */
    MAIN,

    /**
     * Subscriber will be called in a background thread. If posting thread is not the main thread, event handler methods
     * will be called directly in the posting thread. If the posting thread is the main thread, EventBus uses a single
     * background thread, that will deliver all its events sequentially. Event handlers using this mode should try to
     * return quickly to avoid blocking the background thread.
     */
    BACKGROUND,

    /**
     * Event handler methods are called in a separate thread. This is always independent from the posting thread and the
     * main thread. Posting events never wait for event handler methods using this mode. Event handler methods should
     * use this mode if their execution might take some time, e.g. for network access. Avoid triggering a large number
     * of long running asynchronous handler methods at the same time to limit the number of concurrent threads. EventBus
     * uses a thread pool to efficiently reuse threads from completed asynchronous event handler notifications.
     */
    ASYNC
}

我們通過配置，就可以讓 EventBus類， 拿到具體的類型了

在看一下sticky()
我們默認不配置的時候，返回false（代碼中可以知道）
我們例子里面，有一個地方，
Activity還沒有啟動，只要配置sticky = true

priority()
我們暫時還沒有用上，
我們通過看文檔（或者對線程熟悉，名字就可以猜出來），
可以了解到和對應的優先級有關
這里先不扯了

簡單總結

@interface Subscribe
還是挺簡單的，就是3個方法，可以在配置中，傳遞3中參數
（每個都有默認值，所以也可以不配置對應的值）

拿到值以后，和上一篇一樣，
應該有一個地方可以拿到對應的值，再做處理

代碼地址
前面參考的代碼，存放在（use_little_demo中的 eventbus3test）
https://github.com/2954722256/use_little_demo

下一篇我們可以了解Eventbus3代碼分析（五）：getDefault()，register和EventBusBuilder等