Android 使用UsageStatsManager获取前台A

private long mCurrTime = 0;
    private String mForegroundAppPkg = null;
    private SortedMap<Long, UsageStats> mSortedMap = null;
    private TreeMap<Long, UsageEvents.Event> mUsageEventMap = null;
    private List<UsageStats> usageStatsList = null;

    /**
     * 查询应用使用情况
     * @return 得到最后一个触发 ACTIVITY_RESUMED 的 pkgname
     */
    public String getForegroundAppPkg() {
        final String t_ = "getForegroundAppPkg() ";
        if (destroyed) {
            return "";
        }
        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.LOLLIPOP) {
            mCurrTime = System.currentTimeMillis();
            UsageStatsManager usageStatsManager = ((UsageStatsManager) mContext.getSystemService(Context.USAGE_STATS_SERVICE));
            if (usageStatsManager == null) {
                L.d(TAG, t_ + "1 usageStatsManager == null ");
                return null;
            }
            long beginTime = mCurrTime - 1000 * 60 * 60 * 22;
            // We get usage stats for the last 10 seconds
            if (usageStatsList != null)
                usageStatsList.clear();
            usageStatsList = usageStatsManager.queryUsageStats(UsageStatsManager.INTERVAL_DAILY, beginTime, mCurrTime);
// Sort the stats by the last time used
            if (usageStatsList != null && usageStatsList.size() > 0) {
                //Collections.synchronizedSortedMap
                if (mSortedMap == null)
                    mSortedMap = (new TreeMap<Long, UsageStats>());
                mSortedMap.clear();
                for (UsageStats usageStats : usageStatsList) {
                    mSortedMap.put(usageStats.getLastTimeUsed(), usageStats);
                }
                /**
                 * 最后使用的activity的包名
                 */
                String lastActivityUsedPkg = mSortedMap.get(mSortedMap.lastKey())
                        .getPackageName();
                L.d(TAG, t_ + " lastActivityUsedPkg  = " + lastActivityUsedPkg);

                UsageEvents usageEvents = usageStatsManager
                        .queryEvents(beginTime, mCurrTime);
                if (usageEvents == null) {
                    L.d(TAG, t_ + "3 usageEvents == null ");
                    return "";
                }

                if (mUsageEventMap == null)
                    mUsageEventMap = Maps.newTreeMap();
                mUsageEventMap.clear();


                /**
                 * 数字标识, 大于0 表示此app在前台,等于 0 ,在后台
                 */
                int foregroundNum = 0;
                UsageEvents.Event eventTemp = null;
                // get last event
                while (usageEvents.hasNextEvent()) {
                    eventTemp = new UsageEvents.Event();
                    usageEvents.getNextEvent(eventTemp);

                    if (eventTemp == null || eventTemp.getPackageName() == null)
                        continue;


                    if (! eventTemp.getPackageName().equals(lastActivityUsedPkg)) {
                       continue;
                    } else {
                        int eventType = eventTemp.getEventType();
                        if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
                            if (eventType == UsageEvents.Event.ACTIVITY_RESUMED) {
                                foregroundNum++;
                            } else if (eventType == UsageEvents.Event.ACTIVITY_PAUSED) {
                                foregroundNum--;
                                if (foregroundNum < 0)
                                    foregroundNum = 0;
                            }
                        } else if (eventType == UsageEvents.Event.MOVE_TO_FOREGROUND) {
                            foregroundNum++;
                        } else if (eventType == UsageEvents.Event.MOVE_TO_BACKGROUND) {
                            foregroundNum--;
                            if (foregroundNum < 0)
                                foregroundNum = 0;
                        }
                        if (BuildConfig.DEBUG) {
                            mUsageEventMap.put(eventTemp.getTimeStamp(), eventTemp);
                        }
                    }




                }

                if (BuildConfig.DEBUG){
                    long lastKey = mUsageEventMap.lastKey();
                    long firstKey = mUsageEventMap.firstKey();
                    L.d(TAG, t_ + " getNextEvent eventPkg lastPkg = " + mUsageEventMap.get(lastKey).getPackageName()
                            + ",firstPkg = " + mUsageEventMap.get(firstKey).getPackageName()
                            + ", lastKey = " + lastKey
                            + ",firstKey = " + firstKey
                            + ", lastKeyType = " + mUsageEventMap.get(lastKey).getEventType()
                            + ", firstKeyType = " + mUsageEventMap.get(firstKey).getEventType());
                }







                if (foregroundNum > 0) {
                    mForegroundAppPkg = lastActivityUsedPkg;
                }

            } else {
                L.d(TAG, t_ + "2 usageStatsList == null ");
                return null;
            }
        }


        return mForegroundAppPkg;
    }