ActivityLifecycleCallbacks可能很有趣，但是没有很好的文档。

但是，如果您调用registerActivityLifecycleCallbacks()，您应该能够在活动被创建、销毁等时获得回调。您可以为活动调用getComponentName()。

我们可以使用LiveData扩展这个解决方案:

class AppForegroundStateLiveData : LiveData<AppForegroundStateLiveData.State>() {

    private var lifecycleListener: LifecycleObserver? = null

    override fun onActive() {
        super.onActive()
        lifecycleListener = AppLifecycleListener().also {
            ProcessLifecycleOwner.get().lifecycle.addObserver(it)
        }
    }

    override fun onInactive() {
        super.onInactive()
        lifecycleListener?.let {
            this.lifecycleListener = null
            ProcessLifecycleOwner.get().lifecycle.removeObserver(it)
        }
    }

    internal inner class AppLifecycleListener : LifecycleObserver {

        @OnLifecycleEvent(Lifecycle.Event.ON_START)
        fun onMoveToForeground() {
            value = State.FOREGROUND
        }

        @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
        fun onMoveToBackground() {
            value = State.BACKGROUND
        }
    }

    enum class State {
        FOREGROUND, BACKGROUND
    }
}

现在我们可以订阅这个LiveData并捕获所需的事件。例如:

appForegroundStateLiveData.observeForever { state ->
    when(state) {
        AppForegroundStateLiveData.State.FOREGROUND -> { /* app move to foreground */ }
        AppForegroundStateLiveData.State.BACKGROUND -> { /* app move to background */ }
    }
}

基于Martín marconcini的回答(谢谢!)我终于找到了一个可靠(而且非常简单)的解决方案。

public class ApplicationLifecycleHandler implements Application.ActivityLifecycleCallbacks, ComponentCallbacks2 {

    private static final String TAG = ApplicationLifecycleHandler.class.getSimpleName();
    private static boolean isInBackground = false;

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

    @Override
    public void onActivityStarted(Activity activity) {
    }

    @Override
    public void onActivityResumed(Activity activity) {

        if(isInBackground){
            Log.d(TAG, "app went to foreground");
            isInBackground = false;
        }
    }

    @Override
    public void onActivityPaused(Activity activity) {
    }

    @Override
    public void onActivityStopped(Activity activity) {
    }

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

    @Override
    public void onActivityDestroyed(Activity activity) {
    }

    @Override
    public void onConfigurationChanged(Configuration configuration) {
    }

    @Override
    public void onLowMemory() {
    }

    @Override
    public void onTrimMemory(int i) {
        if(i == ComponentCallbacks2.TRIM_MEMORY_UI_HIDDEN){
            Log.d(TAG, "app went to background");
            isInBackground = true;
        }
    }
}

然后将其添加到Application类的onCreate()中

public class MyApp extends android.app.Application {

    @Override
    public void onCreate() {
        super.onCreate();

        ApplicationLifeCycleHandler handler = new ApplicationLifeCycleHandler();
        registerActivityLifecycleCallbacks(handler);
        registerComponentCallbacks(handler);

    }

}

有三种方法可以实现这一点:

单一活动架构 ActivityLifecycleCallback 生命周期观察者和进程生命周期所有者

我在这里写了一篇关于这个的详细文章。希望能有所帮助。

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!

使用ProcessLifecycleOwner，这非常简单

添加这些依赖项

implementation "android.arch.lifecycle:extensions:$project.archLifecycleVersion"
kapt "android.arch.lifecycle:compiler:$project.archLifecycleVersion"

在芬兰湾的科特林:

class ForegroundBackgroundListener : LifecycleObserver {


    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    fun startSomething() {
        Log.v("ProcessLog", "APP IS ON FOREGROUND")
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    fun stopSomething() {
        Log.v("ProcessLog", "APP IS IN BACKGROUND")
    }
}

然后在你的基本活动中:

override fun onCreate() {
        super.onCreate()

        ProcessLifecycleOwner.get()
                .lifecycle
                .addObserver(
                        ForegroundBackgroundListener()
                                .also { appObserver = it })
    }

请看我关于这个主题的文章: https://medium.com/@egek92/how-to-actually-detect-foreground-background-changes-in-your-android-application-without-wanting-9719cc822c48