创建一个扩展Application的类。然后我们可以在其中使用它的重载方法onTrimMemory()。

为了检测应用程序是否进入了后台，我们将使用:

 @Override
    public void onTrimMemory(final int level) {
        if (level == ComponentCallbacks2.TRIM_MEMORY_UI_HIDDEN) { // Works for Activity
            // Get called every-time when application went to background.
        } 
        else if (level == ComponentCallbacks2.TRIM_MEMORY_COMPLETE) { // Works for FragmentActivty
        }
    }

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;
}

My app needs to "reboot" after return from background - show a series of activities, according to client solicitations. After extensive search on how to manage the background/foreground transitions (treated very differently between iOS and Android), I crossed this question. Found very useful help here, specially from the most voted answer and the one flagged as correct. However, simply reinstantiate the root activity EVERY TIME the app enters foreground looked too annoying, when you think about UX. The solution that worked for me, and the one I think's most adequated - based on the Youtube and Twitter apps functionality - was to combine the answers from @GirishNair and @d60402: Calling the timer when the app's trimming memory, as follows:

@Override
public void onTrimMemory(int level) {
    if (stateOfLifeCycle.equals("Stop")) {
        startActivityTransitionTimer();
    }

    super.onTrimMemory(level);
}

我的定时器限制设置为30秒-我正在考虑增加一点。

private final long MAX_ACTIVITY_TRANSITION_TIME = 30000;

当app进入前台，重新启动，或者app被销毁时，调用方法取消定时器。

在应用程序扩展:

@Override
public void onActivityCreated(Activity activity, Bundle arg1) {
    stopActivityTransitionTimer();
    stateOfLifeCycle = "Create";
}

@Override
public void onActivityDestroyed(Activity activity) {
    stopActivityTransitionTimer();
    stateOfLifeCycle = "Destroy";
}

在活动上(最好是在一个基础活动上，由其他活动继承):

@Override
protected void onStart() {
    super.onStart();
    if (App.wasInBackground) {
        stopActivityTransitionTimer();
    }
}

在我的情况下，当应用程序在最大时间后进入前台时，会创建一个新任务，因此stopActivityTransitionTimer()在onActivityCreated()或onActivityDestroyed()上被调用，在应用程序扩展类中-转向不必要调用活动中的方法。 希望能有所帮助。

你可以使用:

onRestart ()

重新开始和重新开始的区别。

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);

    }

}

创建一个扩展Application的类。然后我们可以在其中使用它的重载方法onTrimMemory()。

为了检测应用程序是否进入了后台，我们将使用:

 @Override
    public void onTrimMemory(final int level) {
        if (level == ComponentCallbacks2.TRIM_MEMORY_UI_HIDDEN) { // Works for Activity
            // Get called every-time when application went to background.
        } 
        else if (level == ComponentCallbacks2.TRIM_MEMORY_COMPLETE) { // Works for FragmentActivty
        }
    }