if (tasks != null && !tasks.isEmpty()) {

　　 ComponentName componentName = tasks.get(0).topActivity;

　　if (componentName != null) {

　　　　return componentName.getClassName();

　　　　}

　　}

　　然而getRunningTask方法在Android5.0以上已经被废弃，只会返回自己和系统的一些不敏感的task，不再返回其他应用的task，用此方法来判断自身App是否处于后台，仍然是有效的，但是无法判断其他应用是否位于前台，因为不再能获取信息

2.通过RunningProcess

　　通过runningProcess获取到一个当前正在运行的进程的List，我们遍历这个List中的每一个进程，判断这个进程的一个importance 属性是否是前台进程，并且包名是否与我们判断的APP的包名一样，如果这两个条件都符合，那么这个App就处于前台。

遗憾的是从Andriod5.1版本后getRunningAppProcesses()只能拿到自己的进程信息,所以已经不再适用了.

3.通过ActivityLifecycleCallbacks

AndroidSDK14在Application类里增加了ActivityLifecycleCallbacks，我们可以通过这个Callback拿到App所有Activity的生命周期回调。

public interface ActivityLifecycleCallbacks {

voidonActivityCreated(Activity activity, Bundle savedInstanceState);

voidonActivityStarted(Activity activity);

voidonActivityResumed(Activity activity);

voidonActivityPaused(Activity activity);

voidonActivityStopped(Activity activity);

voidonActivitySaveInstanceState(Activity activity, Bundle outState);

voidonActivityDestroyed(Activity activity);

}

知道这些信息，我们就可以用更官方的办法来解决问题，当然还是利用方案二里的Activity生命周期的特性，我们只需要在Application的onCreate()里去注册上述接口，然后由Activity回调回来运行状态即可。

private ActivityLifecycleCallbacks mActivityLifecycleCallbacks = new ActivityLifecycleCallbacks() {@Overridepublic void onActivityCreated(Activity activity, Bundle savedInstanceState) {}@Overridepublic void onActivityStarted(Activity activity) {Log.d(TAG, "onActivityStarted " + activity.toString());if (CustomActivityManager.getInstance().getTopActivity() == null) {Status.INSTANCE.setSatus(Constant.FG_ACTIVITY, null, null);}}@Overridepublic void onActivityResumed(Activity activity) {Log.d(TAG, "onActivityResumed " + activity.toString());CustomActivityManager.getInstance().addTopActivity(activity);}@Overridepublic void onActivityPaused(final Activity activity) {Log.d(TAG, "onActivityPaused " + activity.toString());CustomActivityManager.getInstance().removeTopActivity(activity);}@Overridepublic void onActivityStopped(final Activity activity) {if (CustomActivityManager.getInstance().getTopActivity() == null) {Status.INSTANCE.setSatus(Constant.BG_ACTIVITY, null, null);}}@Overridepublic void onActivitySaveInstanceState(Activity activity, Bundle outState) {
//            Log.d(TAG, "onActivitySaveInstanceState " + activity.toString());
        }@Overridepublic void onActivityDestroyed(Activity activity) {}};

@TargetApi(Build.VERSION_CODES.LOLLIPOP_MR1)
public static boolean queryUsageStats(Context context, String packageName) {class RecentUseComparator implements Comparator<UsageStats> {@Overridepublic int compare(UsageStats lhs, UsageStats rhs) {return (lhs.getLastTimeUsed() > rhs.getLastTimeUsed()) ? -1 : (lhs.getLastTimeUsed() == rhs.getLastTimeUsed()) ? 0 : 1;}}RecentUseComparator mRecentComp = new RecentUseComparator();long ts = System.currentTimeMillis();UsageStatsManager mUsageStatsManager = (UsageStatsManager) context.getSystemService(Context.USAGE_STATS_SERVICE);List<UsageStats> usageStats = mUsageStatsManager.queryUsageStats(UsageStatsManager.INTERVAL_BEST, ts - 1000 * 10, ts);if (usageStats == null || usageStats.size() == 0) {if (!havePermissionForTest(context)) {Intent intent = new Intent(Settings.ACTION_USAGE_ACCESS_SETTINGS);intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);context.startActivity(intent);Toast.makeText(context, "权限不够\n请打开手机设置，点击安全-高级-有权查看使用情况的应用，开启这个应用的权限",Toast.LENGTH_LONG).show();}return false;}Collections.sort(usageStats, mRecentComp);String currentTopPackage = usageStats.get(0).getPackageName();return currentTopPackage.equals(packageName);
}@TargetApi(Build.VERSION_CODES.LOLLIPOP)
private static boolean havePermissionForTest(Context context) {try {PackageManager packageManager = context.getPackageManager();ApplicationInfo applicationInfo = packageManager.getApplicationInfo(context.getPackageName(), 0);AppOpsManager appOpsManager = (AppOpsManager) context.getSystemService(Context.APP_OPS_SERVICE);int mode = appOpsManager.checkOpNoThrow(AppOpsManager.OPSTR_GET_USAGE_STAGS, applicationInfo.uid, applicationInfo.packageName);return mode == AppOpsManager.MODE_ALLOWED;} catch (PackageManager.NameNotFoundException e) {return true;}
}

public static boolean getFromAccessibilityService(Context context, String packageName) {if (DetectService.isAccessibilitySettingsOn(context)) {DetectService detectService = DetectService.getInstance();String foreground = detectService.getForegroundPackage();Log.d(DEBUG, "当前窗口焦点对应包名为：" + foreground);return packageName.equals(foreground);} else {Intent intent = new Intent(Settings.ACTION_ACCESSIBILITY+SETTINGS);intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);context.startActivity(intent);Toask.makeTexxt(context, "请为App打开辅助功能开关", Toast.LENGTH_SHORT).show();return false;}
}public class DetectService extends AccessibilityService {private static String mForegroundPackageName;private static DetectService mInstatnce = null;private DetectService {}public static DetectService getInstance() {if (mInstance == null) {synchronized (DetectService.class) {if (mInstance == null) {mInstance = new DetectService();}}}return mInstance;}@Overridepublic void onAccessibilityEvent(AccessibilityEvent event) {if (event.getEventType() == AccessibilityEvent.TYPE_WINDOW_STATE_CHANGED) {mForegroundPackageName = event.getPackageName().toString();}}@Overridepublic void onInterrupt() {}public String getForegroundPackageName() {return mForegroundPackageName;}public static boolean isAccessibilitySettingsOn(Context context) {int accessibilityEnabled = 0;try {accessibilityEnabled = Settings.Secure.getInt(context.getContentResolver(), android.provider.Settings.Secure.ACCESSIBILITY_ENABLED);} catch (Settings.SettingNotFoundException e) {Log.d(DEBUG, e.getMessage());}if (accessibilityEnabled == 1) {String services = Settings.Secure.getString(context.getContentResolver(),Setting.Secure.ENABLED_ACCESSIBILITY_SERICES);if (services != null) {return services.toLowerCase().contains(context.getPackageName().toLowerCase());}}return false;}
}