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
其他回答
这里有一个解决方案，通过使用deboning逻辑，确保我们不会得到连续的背景/前景事件。所以，它总是反映一种稳定的背景/前景状态。
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.LifecycleEventObserver
import androidx.lifecycle.LifecycleOwner
import java.util.Timer
import java.util.TimerTask
/**
* An observer class to listen on the app's lifecycle.
*/
class AppLifecycleObserver(
private val onAppGoesToBackground: () -> Unit = {},
private val onAppEntersForeground: () -> Unit = {}
) : LifecycleEventObserver {
private val debounce = DebouncingTimer(timeout = 10)
override fun onStateChanged(source: LifecycleOwner, event: Lifecycle.Event) {
debounce.refresh {
when (event.targetState) {
Lifecycle.State.CREATED -> onAppGoesToBackground()
Lifecycle.State.RESUMED -> onAppEntersForeground()
else -> Unit
}
}
}
fun attach() {
ProcessLifecycleOwner.get().lifecycle.addObserver(this)
}
fun detach() {
ProcessLifecycleOwner.get().lifecycle.removeObserver(this)
}
private class DebouncingTimer(private val timeout: Long) {
private var timer: Timer? = null
fun refresh(job: () -> Unit) {
timer?.cancel()
timer = Timer()
timer?.schedule(object : TimerTask() {
override fun run() = job.invoke()
}, timeout)
}
}
}
只需要创建一个AppLifecycleObserver实例:
private val appLifecycleObserver = AppLifecycleObserver(
onAppGoesToBackground = { // do whatever... },
onAppEntersForeground = { // do whatever... }
)
// Attach the observer when it is needed:
appLifecycleObserver.attach()
// Remove when there is no need to it:
appLifecycleObserver.detach()
不要忘记添加一个合适的依赖版本:
implementation("androidx.lifecycle:lifecycle-process:$lifecycle_version")
我发现了一个很好的方法来检测应用程序是否进入前台或后台。 这是我的代码。 希望这对你有帮助。
/**
* Custom Application which can detect application state of whether it enter
* background or enter foreground.
*
* @reference http://www.vardhan-justlikethat.blogspot.sg/2014/02/android-solution-to-detect-when-android.html
*/
public abstract class StatusApplication extends Application implements ActivityLifecycleCallbacks {
public static final int STATE_UNKNOWN = 0x00;
public static final int STATE_CREATED = 0x01;
public static final int STATE_STARTED = 0x02;
public static final int STATE_RESUMED = 0x03;
public static final int STATE_PAUSED = 0x04;
public static final int STATE_STOPPED = 0x05;
public static final int STATE_DESTROYED = 0x06;
private static final int FLAG_STATE_FOREGROUND = -1;
private static final int FLAG_STATE_BACKGROUND = -2;
private int mCurrentState = STATE_UNKNOWN;
private int mStateFlag = FLAG_STATE_BACKGROUND;
@Override
public void onCreate() {
super.onCreate();
mCurrentState = STATE_UNKNOWN;
registerActivityLifecycleCallbacks(this);
}
@Override
public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
// mCurrentState = STATE_CREATED;
}
@Override
public void onActivityStarted(Activity activity) {
if (mCurrentState == STATE_UNKNOWN || mCurrentState == STATE_STOPPED) {
if (mStateFlag == FLAG_STATE_BACKGROUND) {
applicationWillEnterForeground();
mStateFlag = FLAG_STATE_FOREGROUND;
}
}
mCurrentState = STATE_STARTED;
}
@Override
public void onActivityResumed(Activity activity) {
mCurrentState = STATE_RESUMED;
}
@Override
public void onActivityPaused(Activity activity) {
mCurrentState = STATE_PAUSED;
}
@Override
public void onActivityStopped(Activity activity) {
mCurrentState = STATE_STOPPED;
}
@Override
public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
}
@Override
public void onActivityDestroyed(Activity activity) {
mCurrentState = STATE_DESTROYED;
}
@Override
public void onTrimMemory(int level) {
super.onTrimMemory(level);
if (mCurrentState == STATE_STOPPED && level >= TRIM_MEMORY_UI_HIDDEN) {
if (mStateFlag == FLAG_STATE_FOREGROUND) {
applicationDidEnterBackground();
mStateFlag = FLAG_STATE_BACKGROUND;
}
}else if (mCurrentState == STATE_DESTROYED && level >= TRIM_MEMORY_UI_HIDDEN) {
if (mStateFlag == FLAG_STATE_FOREGROUND) {
applicationDidDestroyed();
mStateFlag = FLAG_STATE_BACKGROUND;
}
}
}
/**
* The method be called when the application been destroyed. But when the
* device screen off,this method will not invoked.
*/
protected abstract void applicationDidDestroyed();
/**
* The method be called when the application enter background. But when the
* device screen off,this method will not invoked.
*/
protected abstract void applicationDidEnterBackground();
/**
* The method be called when the application enter foreground.
*/
protected abstract void applicationWillEnterForeground();
}
如果你的应用由多个活动和/或堆叠的活动组成，就像一个标签栏小部件，那么覆盖onPause()和onResume()将不起作用。例如，当启动一个新的活动，当前的活动将得到暂停之前，新的一个被创建。当完成一个活动(使用“后退”按钮)时，也同样适用。
我发现有两种方法似乎很有效。
第一个需要GET_TASKS权限，由一个简单的方法组成，通过比较包名来检查设备上运行最多的活动是否属于应用程序:
private boolean isApplicationBroughtToBackground() {
ActivityManager am = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
List<RunningTaskInfo> tasks = am.getRunningTasks(1);
if (!tasks.isEmpty()) {
ComponentName topActivity = tasks.get(0).topActivity;
if (!topActivity.getPackageName().equals(context.getPackageName())) {
return true;
}
}
return false;
}
这种方法是在Droid-Fu(现在称为Ignition)框架中发现的。
我自己实现的第二个方法不需要GET_TASKS权限，这很好。相反，它的实现有点复杂。
在MainApplication类中，有一个变量用于跟踪应用程序中正在运行的活动的数量。在onResume()中为每个活动增加变量，在onPause()中减少变量。
当正在运行的activity数量达到0时，如果满足以下条件，应用程序将被放入后台:
正在暂停的活动没有结束(使用了“后退”按钮)。这可以通过使用activity.isFinishing()方法来完成。 没有启动一个新活动(相同的包名)。你可以重写startActivity()方法来设置一个变量来指示这一点，然后在onPostResume()中重置它，这是创建/恢复活动时运行的最后一个方法。
当您可以检测到应用程序已经退出到后台时，当它被带回前台时也很容易检测到。
我在谷歌Analytics EasyTracker中使用了这个，它起作用了。可以将其扩展为使用简单整数来完成您想要的任务。
public class MainApplication extends Application {
int isAppBackgrounded = 0;
@Override
public void onCreate() {
super.onCreate();
appBackgroundedDetector();
}
private void appBackgroundedDetector() {
registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks() {
@Override
public void onActivityCreated(Activity activity, Bundle bundle) {
}
@Override
public void onActivityStarted(Activity activity) {
EasyTracker.getInstance(MainApplication.this).activityStart(activity);
}
@Override
public void onActivityResumed(Activity activity) {
isAppBackgrounded++;
if (isAppBackgrounded > 0) {
// Do something here
}
}
@Override
public void onActivityPaused(Activity activity) {
isAppBackgrounded--;
}
@Override
public void onActivityStopped(Activity activity) {
EasyTracker.getInstance(MainApplication.this).activityStop(activity);
}
@Override
public void onActivitySaveInstanceState(Activity activity, Bundle bundle) {
}
@Override
public void onActivityDestroyed(Activity activity) {
}
});
}
}
您可以在ActivityLifecycleCallbacks和ComponentCallbacks2的帮助下轻松实现这一点。
创建一个实现上述接口的类AppLifeCycleHandler。
package com.sample.app;
import android.app.Activity;
import android.app.Application;
import android.content.ComponentCallbacks2;
import android.content.res.Configuration;
import android.os.Bundle;
/**
* Created by Naveen on 17/04/18
*/
public class AppLifeCycleHandler
implements Application.ActivityLifecycleCallbacks, ComponentCallbacks2 {
AppLifeCycleCallback appLifeCycleCallback;
boolean appInForeground;
public AppLifeCycleHandler(AppLifeCycleCallback appLifeCycleCallback) {
this.appLifeCycleCallback = appLifeCycleCallback;
}
@Override
public void onActivityResumed(Activity activity) {
if (!appInForeground) {
appInForeground = true;
appLifeCycleCallback.onAppForeground();
}
}
@Override
public void onTrimMemory(int i) {
if (i == ComponentCallbacks2.TRIM_MEMORY_UI_HIDDEN) {
appInForeground = false;
appLifeCycleCallback.onAppBackground();
}
}
@Override
public void onActivityCreated(Activity activity, Bundle bundle) {
}
@Override
public void onActivityStarted(Activity activity) {
}
@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() {
}
interface AppLifeCycleCallback {
void onAppBackground();
void onAppForeground();
}
}
在你的类中，当应用程序在前台和后台之间切换时，应用程序实现AppLifeCycleCallback来获得回调。如下图所示。
public class BaseApplication extends Application implements AppLifeCycleHandler.AppLifeCycleCallback{
@Override
public void onCreate() {
super.onCreate();
AppLifeCycleHandler appLifeCycleHandler = new AppLifeCycleHandler(this);
registerActivityLifecycleCallbacks(appLifeCycleHandler);
registerComponentCallbacks(appLifeCycleHandler);
}
@Override
public void onAppBackground() {
Log.d("LifecycleEvent", "onAppBackground");
}
@Override
public void onAppForeground() {
Log.d("LifecycleEvent", "onAppForeground");
}
}
希望这能有所帮助。
编辑 作为替代方案，您现在可以使用生命周期感知的体系结构组件。
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