我试图写一个应用程序，做一些具体的时候，它被带回前台后一段时间。是否有一种方法可以检测应用程序是被发送到后台还是被带到前台?
当前回答
这是我的解决方案。只需在您的主Application类中注册这个ActivityLifecycleCallbacks。在评论中，我提到了一个用户配置文件活动边缘情况。该活动只是一个具有透明边缘的活动。
/**
* This class used Activity lifecycle callbacks to determine when the application goes to the
* background as well as when it is brought to the foreground.
*/
public class Foreground implements Application.ActivityLifecycleCallbacks
{
/**
* How long to wait before checking onStart()/onStop() count to determine if the app has been
* backgrounded.
*/
public static final long BACKGROUND_CHECK_DELAY_MS = 500;
private static Foreground sInstance;
private final Handler mMainThreadHandler = new Handler(Looper.getMainLooper());
private boolean mIsForeground = false;
private int mCount;
public static void init(final Application application)
{
if (sInstance == null)
{
sInstance = new Foreground();
application.registerActivityLifecycleCallbacks(sInstance);
}
}
public static Foreground getInstance()
{
return sInstance;
}
public boolean isForeground()
{
return mIsForeground;
}
public boolean isBackground()
{
return !mIsForeground;
}
@Override
public void onActivityStarted(final Activity activity)
{
mCount++;
// Remove posted Runnables so any Meteor disconnect is cancelled if the user comes back to
// the app before it runs.
mMainThreadHandler.removeCallbacksAndMessages(null);
if (!mIsForeground)
{
mIsForeground = true;
}
}
@Override
public void onActivityStopped(final Activity activity)
{
mCount--;
// A transparent Activity like community user profile won't stop the Activity that launched
// it. If you launch another Activity from the user profile or hit the Android home button,
// there are two onStops(). One for the user profile and one for its parent. Remove any
// posted Runnables so we don't get two session ended events.
mMainThreadHandler.removeCallbacksAndMessages(null);
mMainThreadHandler.postDelayed(new Runnable()
{
@Override
public void run()
{
if (mCount == 0)
{
mIsForeground = false;
}
}
}, BACKGROUND_CHECK_DELAY_MS);
}
@Override
public void onActivityCreated(final Activity activity, final Bundle savedInstanceState)
{
}
@Override
public void onActivityResumed(final Activity activity)
{
}
@Override
public void onActivityPaused(final Activity activity)
{
}
@Override
public void onActivitySaveInstanceState(final Activity activity, final Bundle outState)
{
}
@Override
public void onActivityDestroyed(final Activity activity)
{
}
}
其他回答
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!
编辑:新的体系结构组件带来了一些有希望的东西:ProcessLifecycleOwner，参见@vokilam的回答
实际解决方案根据谷歌I/O谈话:
class YourApplication : Application() {
override fun onCreate() {
super.onCreate()
registerActivityLifecycleCallbacks(AppLifecycleTracker())
}
}
class AppLifecycleTracker : Application.ActivityLifecycleCallbacks {
private var numStarted = 0
override fun onActivityStarted(activity: Activity?) {
if (numStarted == 0) {
// app went to foreground
}
numStarted++
}
override fun onActivityStopped(activity: Activity?) {
numStarted--
if (numStarted == 0) {
// app went to background
}
}
}
是的。我知道很难相信这个简单的解决方案有效，因为我们有这么多奇怪的解决方案。
但还是有希望的。
onPause()和onResume()方法在应用程序被带到后台并再次进入前台时被调用。但是，在应用程序第一次启动时和关闭之前也会调用它们。你可以在活动中阅读更多。
没有任何直接的方法来获得应用程序的状态，而在后台或前台，但即使我已经面临这个问题，并找到解决方案与onWindowFocusChanged和onStop。
更多细节请查看这里Android:解决方案检测当一个Android应用程序去后台，回到前台没有getRunningTasks或getRunningAppProcesses。
下面是我解决这个问题的方法。它的工作前提是，在活动转换之间使用时间参考最有可能提供足够的证据来证明应用程序是否“背景化”。
首先，我使用了一个android.app.Application实例(让我们称它为MyApplication)，它有一个Timer，一个TimerTask，一个常量来表示从一个活动过渡到另一个活动可以合理地花费的最大毫秒数(我用了一个2s的值)，一个布尔值来指示应用程序是否“在后台”:
public class MyApplication extends Application {
private Timer mActivityTransitionTimer;
private TimerTask mActivityTransitionTimerTask;
public boolean wasInBackground;
private final long MAX_ACTIVITY_TRANSITION_TIME_MS = 2000;
...
应用程序还提供了两种方法来启动和停止定时器/任务:
public void startActivityTransitionTimer() {
this.mActivityTransitionTimer = new Timer();
this.mActivityTransitionTimerTask = new TimerTask() {
public void run() {
MyApplication.this.wasInBackground = true;
}
};
this.mActivityTransitionTimer.schedule(mActivityTransitionTimerTask,
MAX_ACTIVITY_TRANSITION_TIME_MS);
}
public void stopActivityTransitionTimer() {
if (this.mActivityTransitionTimerTask != null) {
this.mActivityTransitionTimerTask.cancel();
}
if (this.mActivityTransitionTimer != null) {
this.mActivityTransitionTimer.cancel();
}
this.wasInBackground = false;
}
这个解决方案的最后一部分是从所有活动的onResume()和onPause()事件中添加对这些方法的调用，或者，最好是在所有具体活动继承的基础活动中:
@Override
public void onResume()
{
super.onResume();
MyApplication myApp = (MyApplication)this.getApplication();
if (myApp.wasInBackground)
{
//Do specific came-here-from-background code
}
myApp.stopActivityTransitionTimer();
}
@Override
public void onPause()
{
super.onPause();
((MyApplication)this.getApplication()).startActivityTransitionTimer();
}
所以在这种情况下，当用户只是在你的应用程序的活动之间导航，离开活动的onPause()启动定时器，但几乎立即进入的新活动取消定时器之前，它可以达到最大过渡时间。wasInBackground也是假的。
另一方面，当一个Activity从启动器来到前台，设备被唤醒，结束电话呼叫等，更有可能是定时器任务在此事件之前执行，因此wasInBackground被设置为true。
这是我的解决方案。只需在您的主Application类中注册这个ActivityLifecycleCallbacks。在评论中，我提到了一个用户配置文件活动边缘情况。该活动只是一个具有透明边缘的活动。
/**
* This class used Activity lifecycle callbacks to determine when the application goes to the
* background as well as when it is brought to the foreground.
*/
public class Foreground implements Application.ActivityLifecycleCallbacks
{
/**
* How long to wait before checking onStart()/onStop() count to determine if the app has been
* backgrounded.
*/
public static final long BACKGROUND_CHECK_DELAY_MS = 500;
private static Foreground sInstance;
private final Handler mMainThreadHandler = new Handler(Looper.getMainLooper());
private boolean mIsForeground = false;
private int mCount;
public static void init(final Application application)
{
if (sInstance == null)
{
sInstance = new Foreground();
application.registerActivityLifecycleCallbacks(sInstance);
}
}
public static Foreground getInstance()
{
return sInstance;
}
public boolean isForeground()
{
return mIsForeground;
}
public boolean isBackground()
{
return !mIsForeground;
}
@Override
public void onActivityStarted(final Activity activity)
{
mCount++;
// Remove posted Runnables so any Meteor disconnect is cancelled if the user comes back to
// the app before it runs.
mMainThreadHandler.removeCallbacksAndMessages(null);
if (!mIsForeground)
{
mIsForeground = true;
}
}
@Override
public void onActivityStopped(final Activity activity)
{
mCount--;
// A transparent Activity like community user profile won't stop the Activity that launched
// it. If you launch another Activity from the user profile or hit the Android home button,
// there are two onStops(). One for the user profile and one for its parent. Remove any
// posted Runnables so we don't get two session ended events.
mMainThreadHandler.removeCallbacksAndMessages(null);
mMainThreadHandler.postDelayed(new Runnable()
{
@Override
public void run()
{
if (mCount == 0)
{
mIsForeground = false;
}
}
}, BACKGROUND_CHECK_DELAY_MS);
}
@Override
public void onActivityCreated(final Activity activity, final Bundle savedInstanceState)
{
}
@Override
public void onActivityResumed(final Activity activity)
{
}
@Override
public void onActivityPaused(final Activity activity)
{
}
@Override
public void onActivitySaveInstanceState(final Activity activity, final Bundle outState)
{
}
@Override
public void onActivityDestroyed(final Activity activity)
{
}
}
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