ActivityLifecycleCallbacks，监听前后台状态

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。

public class ForegroundCallbacks implements Application.ActivityLifecycleCallbacks {
public static final long CHECK_DELAY = 500;
public static final String TAG = ForegroundCallbacks.class.getName();
public interface Listener {
public void onBecameForeground();
public void onBecameBackground();
}
private static ForegroundCallbacks instance;
private boolean foreground = false, paused = true;
private Handler handler = new Handler();
private List<Listener> listeners = new CopyOnWriteArrayList<Listener>();
private Runnable check;
public static ForegroundCallbacks init(Application application){
if (instance == null) {
instance = new ForegroundCallbacks();
application.registerActivityLifecycleCallbacks(instance);
}
return instance;
}
public static ForegroundCallbacks get(Application application){
if (instance == null) {
init(application);
}
return instance;
}
public static ForegroundCallbacks get(Context ctx){
if (instance == null) {
Context appCtx = ctx.getApplicationContext();
if (appCtx instanceof Application) {
init((Application)appCtx);
}
throw new IllegalStateException(
"Foreground is not initialised and " +
"cannot obtain the Application object");
}
return instance;
}
public static ForegroundCallbacks get(){
if (instance == null) {
throw new IllegalStateException(
"Foreground is not initialised - invoke " +
"at least once with parameterised init/get");
}
return instance;
}
public boolean isForeground(){
return foreground;
}
public boolean isBackground(){
return !foreground;
}
public void addListener(Listener listener){
listeners.add(listener);
}
public void removeListener(Listener listener){
listeners.remove(listener);
}
@Override
public void onActivityResumed(Activity activity) {
paused = false;
boolean wasBackground = !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");
}
}
@Override
public void onActivityPaused(Activity activity) {
paused = true;
if (check != null)
handler.removeCallbacks(check);
handler.postDelayed(check = new Runnable(){
@Override
public void run() {
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);
}
@Override
public void onActivityCreated(Activity activity, Bundle savedInstanceState) {}
@Override
public void onActivityStarted(Activity activity) {}
@Override
public void onActivityStopped(Activity activity) {}
@Override
public void onActivitySaveInstanceState(Activity activity, Bundle outState) {}
@Override
public void onActivityDestroyed(Activity activity) {}
}

public class MyApplication extends Application{
@Override
public void onCreate() {
super.onCreate();
ForegroundCallbacks.init(this);
ForegroundCallbacks.get().addListener(new ForegroundCallbacks.Listener() {
@Override
public void onBecameForeground() {
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 = new Intent(getApplicationContext(), CheckGesPwdActivity.class);
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP|Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(intent);
}else{
}
}
@Override
public void onBecameBackground() {
L.d("当前程序切换到后台");
}
});
}
}