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    //当前应用是否处于前台
    private boolean isForeground(Context context) {
        if (context != null) {
            ActivityManager activityManager = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
            List<ActivityManager.RunningAppProcessInfo> processes = activityManager.getRunningAppProcesses();
            for (ActivityManager.RunningAppProcessInfo processInfo: processes) {
                if (processInfo.processName.equals(context.getPackageName())) {
                    if (processInfo.importance == ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND) {
                        return true;
                    }
                }
            }
        }
        return false;
    }

可以根据importance的不同来判断前台或后台
RunningAppProcessInfo 里面的常量IMOPORTANCE就是上面所说的前台后台，其实IMOPORTANCE是表示这个app进程的重要性，因为系统回收时候，会根据IMOPORTANCE来回收进程的。具体可以去看文档。。

    public static final int IMPORTANCE_BACKGROUND = 400//后台
    public static final int IMPORTANCE_EMPTY = 500//空进程
    public static final int IMPORTANCE_FOREGROUND = 100//在屏幕最前端、可获取到焦点 可理解为Activity生命周期的OnResume();
    public static final int IMPORTANCE_SERVICE = 300//在服务中
    public static final int IMPORTANCE_VISIBLE = 200//在屏幕前端、获取不到焦点可理解为Activity生命周期的OnStart();

但上面的方法有的机型不支持，下面这个方法还是比较靠谱的，但需要一个权限
< uses-permission Android:name =“android.permission.GET_TASKS” />

    //当前应用是否处于前台
    private boolean isForeground(Context context) {
        if (context != null) {
            ActivityManager am = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
            ComponentName cn = am.getRunningTasks(1).get(0).topActivity;
            String currentPackageName = cn.getPackageName();
            if (!TextUtils.isEmpty(currentPackageName) && currentPackageName.equals(context.getPackageName())) {
                return true;
            }
            return false;
        }
        return false;
    }

版本4.0以上，可以使用ActivityLifecycle

if (Build.VERSION.SDK_INT >= 14) {
            lifecycle = new SimpleActivityLifecycle();
            registerActivityLifecycleCallbacks(lifecycle);

public class SimpleActivityLifecycle implements Application.ActivityLifecycleCallbacks {

    private boolean isForeground = false;//应用是否处于前端

    @Override
    public void onActivityCreated(Activity activity, Bundle savedInstanceState) {

    }

    @Override
    public void onActivityStarted(Activity activity) {

    }

    @Override
    public void onActivityResumed(Activity activity) {
        isForeground = true;
    }

    @Override
    public void onActivityPaused(Activity activity) {
        isForeground = false;
    }

    @Override
    public void onActivityStopped(Activity activity) {

    }

    @Override
    public void onActivitySaveInstanceState(Activity activity, Bundle outState) {

    }

    @Override
    public void onActivityDestroyed(Activity activity) {

    }

    public boolean isForeground() {
        return isForeground;
    }
}