判断当前应用是在前台还是后台

1. 应用场景

接收推送的时候，当我们的APP 收到一条推送的时候，可能在应用内，也可能在应用外。

在应用内的时候，显示一个 Dialog 之类，在应用外的时候，弹一个notifyCation.

2. 如何判断是在显示还是没有显示

2.1 方法一

以前 Android 提供 API 是 getRunningTasks()，拿到所有正在运行的 Task，一个个进行判断。 如果自己的 package 在里面，就是在应用内。

但是每一次都需要 for - loop，比较操蛋，不做介绍

2.1 方法二

Android 4.0 之后 提供 API Application.ActivityLifecycleCallbacks，生命周期执行到哪些，就会回调哪些，

public interface ActivityLifecycleCallbacks {
void onActivityCreated(Activity activity, Bundle savedInstanceState);
void onActivityStarted(Activity activity);
void onActivityResumed(Activity activity);
void onActivityPaused(Activity activity);
void onActivityStopped(Activity activity);
void onActivitySaveInstanceState(Activity activity, Bundle outState);
void onActivityDestroyed(Activity activity);
}

public class AppStatusTracker implements Application.ActivityLifecycleCallbacks{
//用来记录App状态信息
}

每次生命周期变动都会回调，收集起来就可以知道当前应用的状态

如果在应用外，所有的 Activity 都应该 onStop() 掉，或者 onDestroyed()，如果是在应用内，则只有一个 Activity 是 onResumed()。

根据Activity 之间跳转，的生命周期记录

A - -> onPaused()

B - -> onCreated()

B - -> onStarted()

B - -> onResumed()

A - -> onStoped()

A - -> onDestoryed()

//界面要显示时调用此方法，onCreate -- onResume 之间不该写大量代码，
// 防止初始化时间过长会导致黑屏，
//一旦此方法回调，就可以确定当前应用是在前台执行
@Override
public void onActivityResumed(Activity activity) {
L.e(activity.toString()+" onActivityResumed");
//Activity 跳转过程中，onPause -> onResume 之间需要时间，这时候收到消息推送，这算前台？后台？
//onPause() 可能为 false，也可能是要跳转到另外一个Activity，另外一个Activity 去掉用onResumed 方法

isForground = true;
timestamp = 0l;
isScreenOff = false;
}

@Override
public void onActivityStarted(Activity activity) {
L.e(activity.toString()+" onActivityStarted");
activeCount ++;
}

@Override
public void onActivityStopped(Activity activity) {
L.e(activity.toString()+" onActivityStopped");
activeCount --;
if (activeCount == 0){
isForground = false;//在后台执行
timestamp = System.currentTimeMillis();
}
}

3. 代码

public class AppStatusTracker implements Application.ActivityLifecycleCallbacks{

private boolean isForground;
private int activeCount;//计数器，所有的Activity都执行了stop方法，那么count=0,app在后台执行

private static final long MAX_INTERVAL = 5 * 60* 1000;
private long timestamp;//在后台呆的时间够长，再切换到前台的时间差，超过最大值显示图形解锁
private boolean isScreenOff;//图形解锁的特殊需求，屏幕锁住之后再亮起需要图形解锁

private static AppStatusTracker tracker;
private Application application;
private DaemonReceiver receiver;
private int mAppStatus = ConstantValues.STATUS_FORCE_KILLED;

private AppStatusTracker(Application application) {
this.application = application;
application.registerActivityLifecycleCallbacks(this);//必须注册才能接受到该方法的回调
}

public static void init(Application application) {
tracker = new AppStatusTracker(application);
}

public static AppStatusTracker getInstance() {
return tracker;
}

public void setAppStatus(int status) {
this.mAppStatus = status;
if (status == ConstantValues.STATUS_ONLINE){
if (receiver == null){
IntentFilter filter = new IntentFilter();
filter.addAction(Intent.ACTION_SCREEN_OFF);
receiver = new DaemonReceiver();
application.registerReceiver(receiver,filter);
}else if (receiver != null){
application.unregisterReceiver(receiver);
receiver = null;
}
}
}

public int getAppStatus() {
return this.mAppStatus;
}

public boolean isForground() {
return isForground;
}

private void onScreenOff(boolean isScreenOff) {
this.isScreenOff = isScreenOff;
}

public boolean checkIfShowGesture(){
if (mAppStatus == ConstantValues.STATUS_OFFLINE){
if (isScreenOff){
return false;
}
if (timestamp != 0l && System.currentTimeMillis() - timestamp > MAX_INTERVAL) {
return true;
}
}
return false;
}

@Override
public void onActivityStopped(Activity activity) {
L.e(activity.toString()+" onActivityStopped");
activeCount --;
if (activeCount == 0){
isForground = false;//在后台执行
timestamp = System.currentTimeMillis();
}
}

@Override
public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
L.e(activity.toString()+" onActivityCreated");
}

@Override
public void onActivityStarted(Activity activity) {
L.e(activity.toString()+" onActivityStarted");
activeCount ++;
}

//界面要显示时调用此方法，onCreate -- onResume 之间不该写大量代码，
// 防止初始化时间过长会导致黑屏，
//一旦此方法回调，就可以确定当前应用是在前台执行
@Override
public void onActivityResumed(Activity activity) {
L.e(activity.toString()+" onActivityResumed");
//Activity 跳转过程中，onPause -> onResume 需要时间，这过程中算前台？后台？
isForground = true;
timestamp = 0l;
isScreenOff = false;
}

@Override
public void onActivityPaused(Activity activity) {
L.e(activity.toString()+" onActivityPaused");
}

@Override
public void onActivityDestroyed(Activity activity) {
L.e(activity.toString()+" onActivityDestroyed");
}

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

}

private class DaemonReceiver extends BroadcastReceiver{
@Override
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
L.d("onReceive:" + action);
if (Intent.ACTION_SCREEN_OFF.equals(action)) {
AppStatusTracker.getInstance().onScreenOff(true);
}
}
}
}