So I'm using the Observer pattern in my app in order to get notified of changes in another class without having to look for them.
I have a Singleton class which extends Observable. Inside this class I have two CountDownTimer type variables. Eachs of these contains two methods: onTick() and onFinished().
Let's call those Timers A and B for the sake of simplicity.
Every time A.onTick(), A.onFinished(), B.onTick(), B.onFinished() are called, I must call notifyObservers() to notify my Observer that something has changed.
Until here everything works fine. The problem is that I know something has changed, but I don't know what exactly has changed. Depending on which one notified me, I must execute some code on the Observer side.
How do I know which of these methods notified me?
Use LiveData instead of Observable. LiveData is quite useful because not only it's observable but also it binds to your activity's lifecycle so you don't have to worry about handling it yourself.
Maybe this example will help you:
public class MyTimerWrapper {
public static MyTimerWrapper getInstance() {
// Your singleton logic
createTimers();
return instance;
}
private CountDownTimer timerA;
private CountDownTimer timerB;
private MutableLiveData<TimerEvent> timerALiveData = new MutableLiveData<TimerEvent>();
private MutableLiveData<TimerEvent> timerBLiveData = new MutableLiveData<TimerEvent>();
public LiveData<TimerEvent> startTimerA() {
timerA.start();
return timerALiveData;
}
public LiveData<TimerEvent> startTimerB() {
timerB.start();
return timerBLiveData;
}
private void createTimers() {
createTimerA();
createTimerB();
}
private void createTimerA() {
timerA = new CountDownTimer(30000, 1000) {
#Override
public void onTick(long millisUntilFinished) {
// If you're running on another thread
timerALiveData.postValue(TimerEvent.TICK);
// Otherwise
timerALiveData.setValue(TimerEvent.TICK);
}
#Override
public void onFinish() {
// If you're running on another thread
timerALiveData.postValue(TimerEvent.FINISH);
// Otherwise
timerALiveData.setValue(TimerEvent.FINISH);
}
}
}
private void createTimerB() {
// Same as createTimerA, but with timerB
}
}
public enum TimerEvent {
TICK,
FINISH
}
Now to observe that data in your activity:
MyTimerWrapper timerWrapper = MyTimerWrapper.getInstance();
timerWrapper.startTimerA().observe(this, new Observer {
#Override
public void onChanged(TimerEvent timerEvent) {
// Here you'll be able to see whether timerA is ticking or finished
}
})
You can create a custom EventType class and pass it to Observable.notifyObservers(Object arg):
public class EventType {
String eventType; //"onTick" or "onFinish"
TimerType timerType;
EventType(String eventType, TimerType timerType){
this.eventType = eventType;
this.timerType = timerType;
}
}
TimerType is an enum type:
public enum TimerType {
A,
B;
}
and create TimerA and TimerB classes extending CountDownTimer:
private class TimerA extends CountDownTimer {
final EventType onTickEvent = new EventType("onTick", TimerType.A);
final EventType onFinishEvent = new EventType("onFinish", TimerType.A);
#Override
public void onTick(long millisUntilFinished) {
notifyObservers(onTickEvent);
}
#Override
public void onFinish() {
notifyObservers(onFinishEvent)
}
}
The Observerwill receive the EventType instance via its update(Observable o, Object arg); in the arg argument
Related
I have a code in Java, where I should call the overriden method from the constructor of base class.
I understand that it may cause problems according to many references for example:
Calling an overridden method from a parent class ctor
and also
https://medium.com/#rufuszh90/effective-java-item-17-design-and-document-for-inheritance-or-else-prohibit-it-be6041719fbc
The question I have which pattern to use instead?
Adding sample code here is a Task constructor:
public <T extends AbstractCommon & IParent> Task(T parent, String uuid, String version, Set<AbstractNode> exceptions) throws Exception {
Event tef = getExecutionFinishedEvent();
Event tep = getExecutionInProgressEvent();
Event tefailed = getExecutionFailed();
Event tefinishedonallnodes = getExecutionFinishedOnAllNodesEvent();
Event tTimeout = getTimeoutEvent();
Event tNotAllNodesAreAcessible = getNotAllNodesAreAccessible();
Event tNotAllObjectsAreAvailable = getNotAllObjectsAreAvailable();
}
Here is the extending class AbstractRemoteTask and there are some others.
public abstract class AbstractRemoteTask extends Task implements InterNodeProcessor {
public AbstractRemoteTask() {
}
#JsonIgnore
#Override
protected Event getExecutionFinishedEvent() {
return getEvent(Event.EventType.EXECUTION_FINISHED_LOCAL);
}
#JsonIgnore
#Override
protected Event getExecutionFinishedOnAllNodesEvent() {
return getEvent(Event.EventType.EXECUTION_FINISHED_ON_ALL_NODES);
}
#Override
protected Event getExecutionInProgressEvent() {
return getEvent(Event.EventType.EXECUTION_IN_PROGRESS);
}
#JsonIgnore
#Override
protected Event getExecutionFailed() {
return getEvent(Event.EventType.EXECUTION_FAILED);
}
#JsonIgnore
#Override
protected Event getTimeoutEvent() {
return new RemoteEvent(this, getNodeUuid(), Event.EventType.TIMEOUT);
}
#JsonIgnore
#Override
protected Event getNotAllNodesAreAccessible() {
return new RemoteEvent(this, getNodeUuid(), Event.EventType.NOT_ALL_NODES_ARE_ACCESSIBLE);
}
#JsonIgnore
#Override
protected Event getNotAllObjectsAreAvailable() {
return new RemoteEvent(this, getNodeUuid(), Event.EventType.NOT_ALL_OBJECTS_ARE_AVAILABLE);
}
So the question is what is the best pattern to implement this? As the way it is implemented is not recommended.
I know there are similar questions but it still doesn't answer my question in the manner I need for my current situation.
I have three activity presenters that each need to call a certain data remotely which will therefore call the activity presenter back when data arrives. To create this data listener I created an interface listener and since all three Presenters ask for the same data and retrieve it, all three presenters implement this interface listener.
Interface listener:
interface ListenerInterface {
onGotData();
}
Presenter one:
class PresenterOne implements ListenerInterface{
public void getData() {
DataManager dataManager = new DataManager();
dataManager.getData(this);
}
#Override
public void onGotData(Data data) {
//Do something with data
}
}
Presenter two very similar to presenter one:
class PresenterTwo implements ListenerInterface{
public void getData() {
DataManager dataManager = new DataManager();
dataManager.getData(this);
}
#Override
public void onGotData(Data data) {
//Do something with data
}
}
Assume Presenter three is exactly the same as the previous. The data manager class:
class DataManager {
public void getData(final ListenerInterface listener) {
//Gets data
addOnCompleteListener(new OnCompleteListener<Data data > () {
#Override
public void onComplete (#NonNull DataCall < Data > dataCall) {
listener.onGotData(dataCall.getResults());
}
});
}
}
Would doing so someone call all three presenters since the interface is the one doing the calling or only call the presenter that is passed? Is there anything I should worry about if I followed way? If anyone who knows the Android framework well could provide a detailed answer so I could learn from it more that would be great.
The reason I want to do this is I want to communicate through interfaces between classes.
Sorry if this question is simple for some people but I am still learning.
Thank you very much in advance.
you can use RxBus implementation to make global event (e.g. your onGotData).
First you have to create RxBus class.
public class RxBus {
private static RxBus instance;
private PublishSubject<Event> subject = PublishSubject.create();
public static synchronized RxBus getInstance() {
if (instance == null) {
instance = new RxBus();
}
return instance;
}
private RxBus(){}
public void postEvent(Event event){
subject.onNext(event);
}
public Observable<Event> getEvents(){
return subject;
}
}
And now, you should subscribe to it in BaseActivity or something like this (depends or your project structure).
private RxBus rxbus;
private Subscription rxBusSubscription;
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
rxBus = RxBus.getInstance();
}
#Override
protected void onResume() {
super.onResume();
if (shouldSubscribeRxBus()) {
rxBusSubscription = rxBus.getEvents()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(event -> {
if (event.getEventType() == Event.EventType.DATA_RECEIVED) {
onGotData(data);
}
});
}
}
Now implement you onGotData as you want.
When you catch data received call:
class DataManager {
public void getData(final ListenerInterface listener) {
//Gets data
addOnCompleteListener(new OnCompleteListener<Data data > () {
#Override
public void onComplete (#NonNull DataCall < Data > dataCall) {
RxBus.getInstance().postEvent(new GotDataEvent(dataCall.getResults()));
}
});
}
}
You can create your Event classes structure as you want.
I currently have a web soap service method that works fine, but I would like to know how I can convert it to return a confirmation that the message has been received and that the client does not wait until I finish the process.
#Service
#WebService(serviceName =
"getStudents",wsdlLocation="/wsdl/Students.wsdl")
public class StudentsImpl implements Students {
public StudentResponse getStudents(StudentRequest
request) {
**********************
}
}
public class StudentResponse
{
private String status;
private Date timeStamp;
....................
}
I would like to know how I can respond with an "OK" status and also the time.
#WebService
public abstract interface Students
{
#WebResult(name="response")
#XmlElement(required=true, name="request")
public abstract StudentResponse
getStudents(#WebParam(name="request") StudentRequest
request);
}
Hm interestingly enough this seems to the be inverse of the last question I answered, Howto Convert an async call to blocking.
So the steps are:
Execute the blocking call in a new thread.
Introduce a listener interface
Invoke the listener from the thread when the blocking call completed
Introduce a new async wrapper which can be invoked from the caller.
Assuming your blocking call is fooBlocking(), do:
public class MyKoolClass {
// .. kool functionalities here ...
public interface Listener {
void onTaskCompleted(String message);
}
public void fooAsyncWrapper() {
new FooTask(new Listener() {
#Override
public void onTaskCompleted(final String message) {
System.out.println("So complete, bruh" + message);
}
}).start();
}
public static class FooTask extends Thread {
Listener listener;
public FooTask(final Listener listener) {
this.listener = listener;
}
#Override
public void run() {
fooBlocking();
listener.onTaskCompleted("Sup baws.");
}
}
Please note: I am new in this subject.
Suppose I have a class Event.
public class Event {
//constructors, etc.
public void pathFollowed(int location) {
//this method could be called at any time
}
}
And a class called EventManager.
public class EventManager {
private int managerLocation;
private ArrayList<Event> events;
public EventManager() {
events = new ArrayList<Event>();
}
public void addEvent(Event e) {
//THIS IS THE AREA OF INTEREST
events.add(e);
}
}
In the "area of interest" comment, is there any way of setting the value of managerLocation whenever the Event e calls upon pathFollowed(int location). My goal is that when any of the Events in the events arraylist calls pathFollowed(int location) that managerLocation would be set to "location" ("location" referring to the input in the pathfollowed method).
I was originally thinking of over-riding the pathFollowed method, but then I realized this can't be done because by the time the event gets to the addEvent method, it is already instantiated and can't be changed in this manner.
Thanks in advance.
Maybe some kind of listener pattern?
public class Event {
private List<PathListener> pls; //Or just one if you know you'll only need one
//constructors, etc.
public void pathFollowed(int location) {
//this method could be called at any time
for(PathListener pl : pls)
pl.notifyLocation(location);
}
public addPathListener(PathListener pl) {
pls.add(pl);
}
}
EventManager:
public class EventManager implements PathListener {
private int managerLocation;
private ArrayList<Event> events;
public EventManager() {
events = new ArrayList<Event>();
}
public void addEvent(Event e) {
e.addPathListener(this);
events.add(e);
}
#Override
public notifyLocation(int location) { //Of the PathListener interface
managerLocation = location;
}
}
This is just a kind-of-generic example, because I don't know what your purpose is, but maybe it will get you thinking.
I have used listeners with Android and never had any problems, however today when it tried to create a simple listener in Java I am getting NullPointerException, what is the cause of this and how can I fix it?
this includes 3 classes, ListenerMainStart.java, SendMessageClass.java, and ReceiveMessageClass.java
ListenerMainStart.java
public class ListenerMainStart {
public static void main(String[] args) {
new SendMessageClass();
}
}
SendMessageClass.java
public class SendMessageClass {
public OnStringRequestedListener onStringListener;
public Timer timer;
public SendMessageClass() {
timer = new Timer();
timer.schedule(new TimerAction(), 3000);
}
public void SetOnStringRequestedListener(OnStringRequestedListener listener) {
System.out.println("value of onStringListener " + onStringListener.toString());
onStringListener = listener;
}
public interface OnStringRequestedListener {
public void passString(String sendString);
}
public class TimerAction extends TimerTask {
#Override
public void run() {
if (onStringListener!=null){
// pass string to other class, ONSTRINGLISTENER IS ALWASY NULL
onStringListener.passString("string sent from SendMessageclass");
} else {
System.out.println("onStringListener is null");
}
}
}
}
ReceiveMessageClass.java
public class ReceiveMessageClass implements SendMessageClass.OnStringRequestedListener {
SendMessageClass senderClass;
public ReceiveMessageClass() {
// instantiate class
senderClass = new SendMessageClass();
// set the listener to the class
senderClass.SetOnStringRequestedListener(this);
}
#Override
public void passString(String sendString) {
// do action when string is sent from other class
System.out.println("message recevied from other class is " + sendString);
}
}
It looks like you need to call "SetOnStringRequestedListener" before you turn on your timers. As it is, that method never gets called and onStringListener never gets set. You do call that line of code in the receiver, but of course its far too late there. Your main should instantantiate both the receiver and the sender, SetOnStringRequestedListener, and then set off the timers.
SendMessageClass send = new SendMessageClass();
ReceiveMessageClass recv = new ReceiveMessageClass()
send.SetOnStringRequestedListener(recv)
EDIT: Then take out any code in the receiver that references the sender. The idea behind using the listener is that the two classes don't know directly about each other.