Service 的onUnbind在所有的连接断开后才执行，就是这么设计的，所有连接断开后才通知service，为destory作准备。

查看Service onUnbind的定义

543    /**
544     * Called when all clients have disconnected from a particular interface
545     * published by the service.  The default implementation does nothing and
546     * returns false.
547     *
548     * @param intent The Intent that was used to bind to this service,
549     * as given to {@link android.content.Context#bindService
550     * Context.bindService}.  Note that any extras that were included with
551     * the Intent at that point will <em>not</em> be seen here.
552     *
553     * @return Return true if you would like to have the service's
554     * {@link #onRebind} method later called when new clients bind to it.
555     */
556    public boolean onUnbind(Intent intent) {
557        return false;
558    }

注意关键词： all clients have disconnected

那么onBinde是只调用一次么，这也是个问题，可以试验一下看看，

多个客户端连接的时候，只调用一次，可能也是进行了类似的缓存操作，

另外，service没有提供查看连接数量的方法。

参考资料

https://www.cnblogs.com/sjjg/p/5900793.html