在Android 5.0之前版本：

通过RunningTaskInfo类判断（需要额外权限）：

 /**
 *判断当前应用程序处于前台还是后台
 */public static boolean isApplicationBroughtToBackground(final Context context) {
    ActivityManager am = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);    List<RunningTaskInfo> tasks = am.getRunningTasks(1);    if (!tasks.isEmpty()) {
        ComponentName topActivity = tasks.get(0).topActivity;        if (!topActivity.getPackageName().equals(context.getPackageName())) {            return true;
        }
    }    return false;  
 }

需要在AndroidMenitfest.xml文件中添加以下权限

<uses-permission android:name="android.permission.GET_TASKS" />

在Android 5.0 之后由于getRunningTask（）方法被废弃，失效了所以在5.0之后我们用另外一种方法：

通过RunningAppProcessInfo类判断（不需要额外权限）：

public static boolean isBackground(Context context) {

 ActivityManager activityManager = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);List<RunningAppProcessInfo> appProcesses = activityManager.getRunningAppProcesses();for (RunningAppProcessInfo appProcess : appProcesses) {     if (appProcess.processName.equals(context.getPackageName())) {            if (appProcess.importance == RunningAppProcessInfo.IMPORTANCE_BACKGROUND) {
                      Log.e("后台", appProcess.processName);                      return true;
            }else{
                      Log.e("前台", appProcess.processName);                      return false;
            }
       }
}return false;

}

为了适配手机，我们可以写一个适配方法，从而适配系统：

private boolean isAppIsInBackground(Context context) {

   boolean isInBackground = true;  
   ActivityManager am = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);    
   if (Build.VERSION.SDK_INT > Build.VERSION_CODES.KITKAT_WATCH) {  
       List<ActivityManager.RunningAppProcessInfo> runningProcesses = am.getRunningAppProcesses();  
       for (ActivityManager.RunningAppProcessInfo processInfo : runningProcesses) {  
           //前台程序  
           if (processInfo.importance == ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND) {  
               for (String activeProcess : processInfo.pkgList) {  
                   if (activeProcess.equals(context.getPackageName())) {  
                       isInBackground = false;  
                   }  
               }  
           }  
       }  
   } else {  
       List<ActivityManager.RunningTaskInfo> taskInfo = am.getRunningTasks(1);  
       ComponentName componentInfo = taskInfo.get(0).topActivity;  
       if (componentInfo.getPackageName().equals(context.getPackageName())) {  
           isInBackground = false;  
       }  
   }  

   return isInBackground;

}

原文链接：http://www.apkbus.com/blog-942709-77580.html