Android 判断APP前台，后台运行

public void checkAppState() {
    ActivityManager am = (ActivityManager) getSystemService(ACTIVITY_SERVICE);

    String[] activePackages;
    if (Build.VERSION.SDK_INT > Build.VERSION_CODES.KITKAT_WATCH) {
        activePackages = getActivePackages(am);
    } else {
        activePackages = getActivePackagesCompat(am);
    }
    if (activePackages != null) {
        for (String activePackage : activePackages) {
            if (activePackage.equals(getPackageName())) {
                //Calendar app is launched, do something
            }else{

            }
        }
    }
}

protected String[] getActivePackagesCompat(ActivityManager mActivityManager) {
    final List<ActivityManager.RunningTaskInfo> taskInfo = mActivityManager.getRunningTasks(1);
    final ComponentName componentName = taskInfo.get(0).topActivity;
    final String[] activePackages = new String[1];
    activePackages[0] = componentName.getPackageName();
    return activePackages;
}

protected String[] getActivePackages(ActivityManager mActivityManager) {
    final Set<String> activePackages = new HashSet<String>();
    final List<ActivityManager.RunningAppProcessInfo> processInfos = mActivityManager.getRunningAppProcesses();
    for (ActivityManager.RunningAppProcessInfo processInfo : processInfos) {
        if (processInfo.importance == ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND) {
            activePackages.addAll(Arrays.asList(processInfo.pkgList));
        }
    }
    return activePackages.toArray(new String[activePackages.size()]);
}