关于监听程序处于前台还是后台
弄一个BaseActivity，onResume等方法加1减1？这样不好，bug还是有的。
获得所有程序的列表，判断当前程序是否至于前台？不好，而且新SDK有所限制。
广播+服务，牛刀杀鸡。
所以，Application.ActivityLifecycleCallbacks登场，清脆利索，简单大气。
老规矩，先看图：
ges.gif
结构图
Paste_Image.png
菜已上，酒已喝。说说菜怎么做的吧。
一、Application.ActivityLifecycleCallbacks
Application通过ActivityLifecycleCallbacks使用接口提供了一套回调方法，用于让开发者对Activity的生命周期事件进行集中处理。 ActivityLifecycleCallbacks接口回调可以简化监测Activity的生命周期事件，在一个类中作统一处理。 ActivityLifecycleCallbacks使用要求API 14+ （Android 4.0+）。
既然是接口，那么来实现以下看看怎样呗
随便写一个类，比如名为TestAppCb，实现Application.ActivityLifecycleCallbacks接口
publicclassTestAppCbimplementsApplication.ActivityLifecycleCallbacks{@OverridepublicvoidonActivityCreated(Activity activity, Bundle savedInstanceState){ }@OverridepublicvoidonActivityStarted(Activity activity){ }@OverridepublicvoidonActivityResumed(Activity activity){ }@OverridepublicvoidonActivityPaused(Activity activity){ }@OverridepublicvoidonActivityStopped(Activity activity){ }@OverridepublicvoidonActivitySaveInstanceState(Activity activity, Bundle outState){ }@OverridepublicvoidonActivityDestroyed(Activity activity){ }}
我们发现了很多跟Activity很声明周期很相似的方法。作用不赘述，下面会附上一个名为ForegroundCallbacks的实现类，自行参考。
以往若需监测Activity的生命周期事件代码，你可能是这样做的，重写每一个Acivity的onResume()，然后作统计和处理，ActivityLifecycleCallbacks接口回调可以简化这一繁琐过程，在一个类中作统一处理。
二、具体使用
核心封装类，根据下面的代码的封装，结合自定义的Application，就可以轻松地实现监听程序处于前台还是后台的需求。
publicclassForegroundCallbacksimplementsApplication.ActivityLifecycleCallbacks{publicstaticfinallongCHECK_DELAY =500;publicstaticfinalString TAG = ForegroundCallbacks.class.getName();publicinterfaceListener{publicvoidonBecameForeground();publicvoidonBecameBackground(); }privatestaticForegroundCallbacks instance;privatebooleanforeground =false, paused =true;privateHandler handler =newHandler();privateList listeners =newCopyOnWriteArrayList();privateRunnable check;publicstaticForegroundCallbacksinit(Application application){if(instance ==null) { instance =newForegroundCallbacks(); application.registerActivityLifecycleCallbacks(instance); }returninstance; }publicstaticForegroundCallbacksget(Application application){if(instance ==null) { init(application); }returninstance; }publicstaticForegroundCallbacksget(Context ctx){if(instance ==null) { Context appCtx = ctx.getApplicationContext();if(appCtxinstanceofApplication) { init((Application)appCtx); }thrownewIllegalStateException("Foreground is not initialised and "+"cannot obtain the Application object"); }returninstance; }publicstaticForegroundCallbacksget(){if(instance ==null) {thrownewIllegalStateException("Foreground is not initialised - invoke "+"at least once with parameterised init/get"); }returninstance; }publicbooleanisForeground(){returnforeground; }publicbooleanisBackground(){return!foreground; }publicvoidaddListener(Listener listener){ listeners.add(listener); }publicvoidremoveListener(Listener listener){ listeners.remove(listener); }@OverridepublicvoidonActivityResumed(Activity activity){ paused =false;booleanwasBackground = !foreground; foreground =true;if(check !=null) handler.removeCallbacks(check);if(wasBackground){ L.d ("went foreground");for(Listener l : listeners) {try{ l.onBecameForeground(); }catch(Exception exc) { L.d ("Listener threw exception!:"+exc.toString()); } } }else{ L.d ("still foreground"); } }@OverridepublicvoidonActivityPaused(Activity activity){ paused =true;if(check !=null) handler.removeCallbacks(check); handler.postDelayed(check =newRunnable(){@Overridepublicvoidrun(){if(foreground && paused) { foreground =false; L.d ("went background");for(Listener l : listeners) {try{ l.onBecameBackground(); }catch(Exception exc) { L.d ("Listener threw exception!:"+exc.toString()); } } }else{ L.d ("still foreground"); } } }, CHECK_DELAY); }@OverridepublicvoidonActivityCreated(Activity activity, Bundle savedInstanceState){}@OverridepublicvoidonActivityStarted(Activity activity){}@OverridepublicvoidonActivityStopped(Activity activity){}@OverridepublicvoidonActivitySaveInstanceState(Activity activity, Bundle outState){}@OverridepublicvoidonActivityDestroyed(Activity activity){}}
.
.
MyApplication 结合Application.ActivityLifecycleCallbacks
监听如此轻松
publicclassMyApplicationextendsApplication{@OverridepublicvoidonCreate(){super.onCreate(); ForegroundCallbacks.init(this); ForegroundCallbacks.get().addListener(newForegroundCallbacks.Listener() {@OverridepublicvoidonBecameForeground(){ L.d("当前程序切换到前台");if(CacheUtils.getBoolean(getApplicationContext(), MyConst.GESTRUE_IS_LIVE)){ L.d("已经开启手势锁"); Intent intent =newIntent(getApplicationContext(), CheckGesPwdActivity.class); intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP|Intent.FLAG_ACTIVITY_NEW_TASK); startActivity(intent); }else{ } }@OverridepublicvoidonBecameBackground(){ L.d("当前程序切换到后台"); } }); }}
如上，即可，手势库可以直接引用做个小demo。
整个过程实现起来都是相当轻松的，亮点是ForegroundCallbacks，里面的代码值得咀嚼和学习。
本文粗糙了点，哈哈哈哈，不过我为什么感觉我还是挺良心的，哈哈哈哈。
附上github链接GestureLockMaster
三、单个Activity单独使用？
就在一个页面监听，当然可以。
publicclassTestLifeAcextendsAppCompatActivityimplementsForegroundCallbacks.Listener{@OverrideprotectedvoidonCreate(@Nullable Bundle savedInstanceState){super.onCreate(savedInstanceState); setContentView(R.layout.activity_city_list);// 注册监听ForegroundCallbacks.get(this).addListener(this); }@OverrideprotectedvoidonDestroy(){super.onDestroy();// 移除监听ForegroundCallbacks.get(this).removeListener(this); }@OverridepublicvoidonBecameForeground(Activity activity){// 切换为前台}@OverridepublicvoidonBecameBackground(Activity activity){//切换为后台}}
四，参考学习
Is my Android app currently foreground or background?
本篇完。
作者：阿敏其人
链接：https://www.jianshu.com/p/e7f64e6bc2cc
来源：简书
简书著作权归作者所有，任何形式的转载都请联系作者获得授权并注明出处。
