Android 程序进入后台 恢复到前台

用户点击home键程序进入后台，此时用户再点击图标或在最近运行程序中打开程序，程序进入前台，有没有一个简单方便的方法来实现监听状态变化呢？
有人说监听home键，也有人说所有Activity继承一个BaseActivity，我的方法是通过Application里的registerActivityLifecycleCallbacks，
ActivityLifecycleCallbacks可以监听程序里所有Activity的生命周期方法，Activity执行onStart时存入List，onStop时从List中移除，
当List的size为0时说明程序进入后台。
我这里还有一个LIst用来存放所有没被finish掉的Activity，onCreate时存入，onDestory时移除，用于关闭程序或退出登录时批量关闭Activity。直接看代码吧

public class CustomApplication extends MultiDexApplication {
    Context mContext;
    private static CustomApplication instance;
    public static List<Activity> activityList;//用于关闭程序、退出登录
    private List<Activity> mList;
    private boolean mIsAppOnForeground;//程序在前台运行

    public static synchronized CustomApplication getInstance() {
        return instance;
    }

    @Override
    public void onCreate() {
        super.onCreate();
        instance = this;
        mContext = this.getApplicationContext();
        activityList = new ArrayList<Activity>();
        mList = new ArrayList<Activity>();
        mIsAppOnForeground = false;
        JodaTimeAndroid.init(this);
        initImageLoader();
        this.registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks() {
            @Override
            public void onActivityCreated(Activity activity, Bundle bundle) {
                if (!activityList.contains(activity)) {
                    activityList.add(activity);
                }
            }

            @Override
            public void onActivityStarted(Activity activity) {
                if (!mList.contains(activity)) {
                    mList.add(activity);
                }
                if (!mIsAppOnForeground) {
                    updateJpushInfo();
                    mIsAppOnForeground = true;
                }
            }

            @Override
            public void onActivityResumed(Activity activity) {
            }

            @Override
            public void onActivityPaused(Activity activity) {
            }

            @Override
            public void onActivityStopped(Activity activity) {

                if (mList.contains(activity)) {                    mList.remove(activity);                }                if (mList.size() == 0) {                    mIsAppOnForeground = false;                }            }            @Override            public void onActivitySaveInstanceState(Activity activity, Bundle bundle) {            }            @Override            public void onActivityDestroyed(Activity activity) {                if (activityList.contains(activity)) {                    activityList.remove(activity);                }            }        });    }    @Override    public void onTerminate() {        super.onTerminate();    }}