文章转载于（内容也是从下面出来）
https://blog.csdn.net/zhufuing/article/details/53007705

1、编写MyLifecycleHandler.java文件

public class MyLifecycleHandler implements Application.ActivityLifecycleCallbacks {
    private static int resumed;
    private static int paused;
    private static int started;
    private static int stopped;

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

    @Override
    public void onActivityStarted(Activity activity) {
        ++started;
    }

    @Override
    public void onActivityResumed(Activity activity) {
        ++resumed;
    }

    @Override
    public void onActivityPaused(Activity activity) {
        ++paused;
        android.util.Log.w("test", "application is in foreground: " + (resumed > paused));
    }

    @Override
    public void onActivityStopped(Activity activity) {
        ++stopped;
        android.util.Log.w("test", "application is visible: " + (started > stopped));
    }

    @Override
    public void onActivityDestroyed(Activity activity) {
    }

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

    public static boolean isApplicationVisible() {
        return started > stopped;
    }

    public static boolean isApplicationInForeground() {
    // 当所有 Activity 的状态中处于 resumed 的大于 paused 状态的，即可认为有Activity处于前台状态中 
        return resumed > paused;
    }
}

2、自己定义的Application中注册

registerActivityLifecycleCallbacks(new MyLifecycleHandler());

3、调用方法判断

boolean inForeground = MyLifecycleHandler.isApplicationInForeground();