以前管理已打开的activity，就是在BaseApplication中放一个集合，然后在BaseActivity的OnCreate（）往集合中添加activity，onDestory（）删除集合中的该activity，OnResume（）等其他生命周期中控制activity集合。
然而，最近在看开源项目源码时
https://github.com/bingoogolapple/BGASwipeBackLayout-Android
（仿微信滑动返回）
发现了一个新用法，application自带了ActivityLifecycleCallbacks接口回调来管理已打开的activity，果断涨姿势了>~<
方式比之前的更加简单优雅，代码如下：
public class CommonApplication extends Application {
private Stack<Activity> stack = new Stack<>();
@Override
public void onCreate() {
super.onCreate();
registerActivityLifecycleCallbacks(new CommonActivityLifecycleCallbacks());
}
private class CommonActivityLifecycleCallbacks implements ActivityLifecycleCallbacks{
@Override
public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
stack.add(activity);
}
@Override
public void onActivityStarted(Activity activity) {
}
@Override
public void onActivityResumed(Activity activity) {
}
@Override
public void onActivityPaused(Activity activity) {
}
@Override
public void onActivityStopped(Activity activity) {
}
@Override
public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
}
@Override
public void onActivityDestroyed(Activity activity) {
stack.remove(activity);
}
}
}
