您可以使用ProcessLifecycleOwner将生命周期观察者附加到它。

  public class ForegroundLifecycleObserver implements LifecycleObserver {

    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
    public void onAppCreated() {
        Timber.d("onAppCreated() called");
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    public void onAppStarted() {
        Timber.d("onAppStarted() called");
    }

    @OnLifecycleEvent(Event.ON_RESUME)
    public void onAppResumed() {
        Timber.d("onAppResumed() called");
    }

    @OnLifecycleEvent(Event.ON_PAUSE)
    public void onAppPaused() {
        Timber.d("onAppPaused() called");
    }

    @OnLifecycleEvent(Event.ON_STOP)
    public void onAppStopped() {
        Timber.d("onAppStopped() called");
    }
}

然后在你的Application类的onCreate()你调用这个:

ProcessLifecycleOwner.get().getLifecycle().addObserver(new ForegroundLifecycleObserver());

有了它，你将能够捕捉应用程序在后台运行时发生的ON_PAUSE和ON_STOP事件。

在你的应用程序中添加回调并检查根活动，如下所示:

@Override
public void onCreate() {
    super.onCreate();
    registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks() {
        @Override
        public void onActivityStopped(Activity activity) {
        }

        @Override
        public void onActivityStarted(Activity activity) {
        }

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

        @Override
        public void onActivityResumed(Activity activity) {
        }

        @Override
        public void onActivityPaused(Activity activity) {
        }

        @Override
        public void onActivityDestroyed(Activity activity) {
        }

        @Override
        public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
            if (activity.isTaskRoot() && !(activity instanceof YourSplashScreenActivity)) {
                Log.e(YourApp.TAG, "Reload defaults on restoring from background.");
                loadDefaults();
            }
        }
    });
}

这是我的解决方案https://github.com/doridori/AndroidUtils/blob/master/App/src/main/java/com/doridori/lib/app/ActivityCounter.java

基本上涉及到用计时器计算所有Activity的生命周期方法，以捕捉当前前台没有活动但应用程序(即在旋转)的情况

The principal problem is that you have to get an specific behavior when you start an activity from background. If you override your onPause() and onResume() methods, you'll have a close answer, but not the solution. The problem is that onPause() and onResume() methods are called even if you don't minimize your application, they can be called when you start an activity and later you press the back button to return to your activity. To eliminate that problem and to know really when your application comes from background, you must to get the running process and compare with your process:

private boolean isApplicationBroughtToBackground() {
    ActivityManager am = (ActivityManager) getSystemService(Context.ACTIVITY_SERVICE);
    List<RunningTaskInfo> tasks = am.getRunningTasks(1);
    if (!tasks.isEmpty()) {
        ComponentName topActivity = tasks.get(0).topActivity;
        if (!topActivity.getPackageName().equals(getPackageName())) {
            return true;
        }
    }
    return false;
}

现在你必须声明一个布尔变量:

public boolean wasPaused = false;

并询问你的活动何时进入后台:

@Override
public void onPause(){
    super.onPause();
    if(isApplicationBroughtToBackground())
        wasPaused = true;
}

现在，当你的活动再次出现在屏幕上时，在onResume()方法中询问:

@Override
public void onResume(){
    super.onResume();
    if(wasPaused){
        lockScreen(true);
    }
    wasPaused = false;
}

就是这样。现在，当您的活动进入后台，稍后用户将其带到前台时，锁定屏幕将出现。

如果你想为你的应用程序的任何活动重复这个行为，你必须创建一个活动(可以是BaseActivity)，放这个方法，你所有的活动都必须从BaseActivity继承。

我希望这对你有帮助。

问候!

我所做的是确保所有应用程序内的活动启动startActivityForResult，然后检查onActivityResult是否在onResume之前被调用。如果不是，这意味着我们刚刚从应用程序之外的某个地方返回。

boolean onActivityResultCalledBeforeOnResume;

@Override
public void startActivity(Intent intent) {
    startActivityForResult(intent, 0);
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent intent) {
    super.onActivityResult(requestCode, resultCode, intent);
    onActivityResultCalledBeforeOnResume = true;
}

@Override
protected void onResume() {
    super.onResume();
    if (!onActivityResultCalledBeforeOnResume) {
        // here, app was brought to foreground
    }
    onActivityResultCalledBeforeOnResume = false;
}

这些答案似乎不正确。当另一个活动开始和结束时，也会调用这些方法。你能做的是保留一个全局标志(是的，全局不好:)，并在每次启动一个新活动时将其设置为true。在每个活动的onCreate中将其设置为false。然后，在onPause中检查这个标志。如果为假，你的应用就会进入后台，或者被杀死。