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//当前应用是否处于前台
private boolean isForeground(Context context) {
if (context != null) {
ActivityManager activityManager = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
List<ActivityManager.RunningAppProcessInfo> processes = activityManager.getRunningAppProcesses();
for (ActivityManager.RunningAppProcessInfo processInfo: processes) {
if (processInfo.processName.equals(context.getPackageName())) {
if (processInfo.importance == ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND) {
return true;
}
}
}
}
return false;
}

可以根据importance的不同来判断前台或后台
RunningAppProcessInfo 里面的常量IMOPORTANCE就是上面所说的前台后台，其实IMOPORTANCE是表示这个app进程的重要性，因为系统回收时候，会根据IMOPORTANCE来回收进程的。具体可以去看文档。。

public static final int IMPORTANCE_BACKGROUND = 400//后台
public static final int IMPORTANCE_EMPTY = 500//空进程
public static final int IMPORTANCE_FOREGROUND = 100//在屏幕最前端、可获取到焦点 可理解为Activity生命周期的OnResume();
public static final int IMPORTANCE_SERVICE = 300//在服务中
public static final int IMPORTANCE_VISIBLE = 200//在屏幕前端、获取不到焦点可理解为Activity生命周期的OnStart();

但上面的方法有的机型不支持，下面这个方法还是比较靠谱的，但需要一个权限
< uses-permission Android:name =“android.permission.GET_TASKS” />

//当前应用是否处于前台
private boolean isForeground(Context context) {
if (context != null) {
ActivityManager am = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
ComponentName cn = am.getRunningTasks(1).get(0).topActivity;
String currentPackageName = cn.getPackageName();
if (!TextUtils.isEmpty(currentPackageName) && currentPackageName.equals(context.getPackageName())) {
return true;
}
return false;
}
return false;
}

版本4.0以上，可以使用ActivityLifecycle

if (Build.VERSION.SDK_INT >= 14) {
lifecycle = new SimpleActivityLifecycle();
registerActivityLifecycleCallbacks(lifecycle);

public class SimpleActivityLifecycle implements Application.ActivityLifecycleCallbacks {

private boolean isForeground = false;//应用是否处于前端

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

}

@Override
public void onActivityStarted(Activity activity) {

}

@Override
public void onActivityResumed(Activity activity) {
isForeground = true;
}

@Override
public void onActivityPaused(Activity activity) {
isForeground = false;
}

@Override
public void onActivityStopped(Activity activity) {

}

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

}

@Override
public void onActivityDestroyed(Activity activity) {

}

public boolean isForeground() {
return isForeground;
}
}

Android判断App是否在前台运行