这篇旧文章的另一个解决方案(对那些可能有帮助的人来说):

<application android:name=".BaseApplication" ... >

public class BaseApplication extends Application {

    private class Status {
        public boolean isVisible = true;
        public boolean isFocused = true;
    }

    private Map<Activity, Status> activities;

    @Override
    public void onCreate() {
        activities = new HashMap<Activity, Status>();
        super.onCreate();
    }

    private boolean hasVisibleActivity() {
        for (Status status : activities.values())
            if (status.isVisible)
                return true;
        return false;
    }

    private boolean hasFocusedActivity() {
        for (Status status : activities.values())
            if (status.isFocused)
                return true;
        return false;
    }

    public void onActivityCreate(Activity activity, boolean isStarting) {
        if (isStarting && activities.isEmpty())
            onApplicationStart();
        activities.put(activity, new Status());
    }

    public void onActivityStart(Activity activity) {
        if (!hasVisibleActivity() && !hasFocusedActivity())
            onApplicationForeground();
        activities.get(activity).isVisible = true;
    }

    public void onActivityWindowFocusChanged(Activity activity, boolean hasFocus) {
        activities.get(activity).isFocused = hasFocus;
    }

    public void onActivityStop(Activity activity, boolean isFinishing) {
        activities.get(activity).isVisible = false;
        if (!isFinishing && !hasVisibleActivity() && !hasFocusedActivity())
            onApplicationBackground();
    }

    public void onActivityDestroy(Activity activity, boolean isFinishing) {
        activities.remove(activity);
        if(isFinishing && activities.isEmpty())
            onApplicationStop();
    }

    private void onApplicationStart() {Log.i(null, "Start");}
    private void onApplicationBackground() {Log.i(null, "Background");}
    private void onApplicationForeground() {Log.i(null, "Foreground");}
    private void onApplicationStop() {Log.i(null, "Stop");}

}

public class MyActivity extends BaseActivity {...}

public class BaseActivity extends Activity {

    private BaseApplication application;

    @Override
    protected void onCreate(Bundle state) {
        application = (BaseApplication) getApplication();
        application.onActivityCreate(this, state == null);
        super.onCreate(state);
    }

    @Override
    protected void onStart() {
        application.onActivityStart(this);
        super.onStart();
    }

    @Override
    public void onWindowFocusChanged(boolean hasFocus) {
        application.onActivityWindowFocusChanged(this, hasFocus);
        super.onWindowFocusChanged(hasFocus);
    }

    @Override
    protected void onStop() {
        application.onActivityStop(this, isFinishing());
        super.onStop();
    }

    @Override
    protected void onDestroy() {
        application.onActivityDestroy(this, isFinishing());
        super.onDestroy();
    }

}

这篇旧文章的另一个解决方案(对那些可能有帮助的人来说):

<application android:name=".BaseApplication" ... >

public class BaseApplication extends Application {

    private class Status {
        public boolean isVisible = true;
        public boolean isFocused = true;
    }

    private Map<Activity, Status> activities;

    @Override
    public void onCreate() {
        activities = new HashMap<Activity, Status>();
        super.onCreate();
    }

    private boolean hasVisibleActivity() {
        for (Status status : activities.values())
            if (status.isVisible)
                return true;
        return false;
    }

    private boolean hasFocusedActivity() {
        for (Status status : activities.values())
            if (status.isFocused)
                return true;
        return false;
    }

    public void onActivityCreate(Activity activity, boolean isStarting) {
        if (isStarting && activities.isEmpty())
            onApplicationStart();
        activities.put(activity, new Status());
    }

    public void onActivityStart(Activity activity) {
        if (!hasVisibleActivity() && !hasFocusedActivity())
            onApplicationForeground();
        activities.get(activity).isVisible = true;
    }

    public void onActivityWindowFocusChanged(Activity activity, boolean hasFocus) {
        activities.get(activity).isFocused = hasFocus;
    }

    public void onActivityStop(Activity activity, boolean isFinishing) {
        activities.get(activity).isVisible = false;
        if (!isFinishing && !hasVisibleActivity() && !hasFocusedActivity())
            onApplicationBackground();
    }

    public void onActivityDestroy(Activity activity, boolean isFinishing) {
        activities.remove(activity);
        if(isFinishing && activities.isEmpty())
            onApplicationStop();
    }

    private void onApplicationStart() {Log.i(null, "Start");}
    private void onApplicationBackground() {Log.i(null, "Background");}
    private void onApplicationForeground() {Log.i(null, "Foreground");}
    private void onApplicationStop() {Log.i(null, "Stop");}

}

public class MyActivity extends BaseActivity {...}

public class BaseActivity extends Activity {

    private BaseApplication application;

    @Override
    protected void onCreate(Bundle state) {
        application = (BaseApplication) getApplication();
        application.onActivityCreate(this, state == null);
        super.onCreate(state);
    }

    @Override
    protected void onStart() {
        application.onActivityStart(this);
        super.onStart();
    }

    @Override
    public void onWindowFocusChanged(boolean hasFocus) {
        application.onActivityWindowFocusChanged(this, hasFocus);
        super.onWindowFocusChanged(hasFocus);
    }

    @Override
    protected void onStop() {
        application.onActivityStop(this, isFinishing());
        super.onStop();
    }

    @Override
    protected void onDestroy() {
        application.onActivityDestroy(this, isFinishing());
        super.onDestroy();
    }

}

我建议你仔细阅读这个页面:http://developer.android.com/reference/android/app/Activity.html

简而言之，你的活动在onStop()被调用后不再可见。

简单直接的回答:

override fun onPause() {
    Log.i("APP LIFECYCLE", "App Enter BACKground")
    isForeground = false
    super.onPause()
}

override fun onResume() {
    Log.i("APP LIFECYCLE", "App Enter FOREground")
    isForeground = true
    super.onResume()
}

然后只需使用您的活动的isForeground属性来检查状态。

fun isAppInForeground(): Boolean {
    val activityManager = getSystemService(Context.ACTIVITY_SERVICE) as ActivityManager ?: return false

    val appProcesses = activityManager.runningAppProcesses ?: return false

    val packageName = packageName
    for (appProcess in appProcesses) {
        if (appProcess.importance == ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND && appProcess.processName == packageName) {
            return true
        }
    }

    return false
}

这样怎么样:

boolean isBackgrounded() {
    try {
        context.startService(new Intent(action));
        return false;
    }
    catch (IllegalStateException exc) {
        // "Not allowed to start service Intent: app is in background"
        return true;
    }
}