There are two major differences between Observer/Observable and Publisher/Subscriber patterns: Observer/Observable pattern is mostly implemented in a synchronous way, i.e. the observable calls the appropriate method of all its observers when some event occurs. The Publisher/Subscriber pattern is mostly implemented in an asynchronous way (using message queue). In the Observer/Observable pattern, the observers are aware … Read more
How can I set up my Activity to be listening to the Service? Is this the best way to approach this problem? You have three major options, as I see it: Polling. The Activity periodically asks the Service for the latest data. IMHO, this option sucks, but it’s certainly possible. Callbacks. Per jax’s answer, the … Read more
Program Structure This is how I did it. The Eventbus lets presenters (extending the abstract class Subscriber) subscribe to events belonging to different modules in my app. Each module corresponds to a component in my system, and each module has an event type, a presenter, a handler, a view and a model. A presenter subscribing … Read more
Yes, you can. There are tons of ways to do it. And there is no need to use the “evil” eval function (please yahoogle why it should be avoided) as pointed out here: http://javascript.about.com/library/bleval.htm var tmpFunc = new Function(codeToRun); tmpFunc(); Whether it was JSON at any stage should be irrelevant.
Why is that? Does it mean that we shouldn’t implement observer pattern anymore? Answering the latter part first – YES, it does mean you shouldn’t implement Observer and Obervables anymore. Why were they deprecated – They didn’t provide a rich enough event model for applications. For example, they could support only the notion that something … Read more
As noted here, the JavaFX architecture tends to favor binding GUI elements via classes that implement the Observable interface. Toward this end, Irina Fedortsova has adapted the original Converter to JavaFX in Chapter 5 of JavaFX for Swing Developers: Implementing a Swing Application in JavaFX. I’ve recapitulated the program below, updating to Java 8 and … Read more
You have a concrete example of a Student and a MessageBoard. The Student registers by adding itself to the list of Observers that want to be notified when a new Message is posted to the MessageBoard. When a Message is added to the MessageBoard, it iterates over its list of Observers and notifies them that … Read more
However it does lack flexibility. Well… actually, this looks like a good design to me if an asynchronous API is what you want. It usually is. Maybe all you need is to switch from stderr to Python’s logging module, which has a sort of publish/subscribe model of its own, what with Logger.addHandler() and so on. … Read more
The observer pattern is usually implemented with events. Here’s an example: using System; class Observable { public event EventHandler SomethingHappened; public void DoSomething() => SomethingHappened?.Invoke(this, EventArgs.Empty); } class Observer { public void HandleEvent(object sender, EventArgs args) { Console.WriteLine(“Something happened to ” + sender); } } class Test { static void Main() { Observable observable = … Read more
You need to use the Observer Pattern. In the following code, a person subscribes to receive updates from the global wealth entity. When there is a change to global wealth, this entity then alerts all its subscribers (observers) that a change happened. Person then updates itself. I make use of properties in this example, but … Read more