In a digital signal acquisition system, often data is pushed into an observer in the system by one thread. example from Wikipedia/Observer_pattern: foreach (IObserver observer in observers) observer.Update(message); When e.g. a user action from e.g. a GUI-thread requires the data to stop flowing, you want to break the subject-o...
I'm trying to log users out when the user's session timeout happens. Logging users out - in my case - requires modifying the user's "online" status in a database. I was thinking that I might be able to use the observer pattern to make something that would monitor the state of the user session and trigger a callback when the session expi...
Is it possible to have multiple listeners to messages carried by MSMQ? WCF appears to frame everything in terms of services, making communication a point-to-point affair. I want to use a message queue to buffer incoming traffic for another process that records the logs in a database. There can be be any number of other processes inter...
Suppose I want to create a set of observers based on type. That is to say, when they are notified of an event, they are told the type of one of the arguments and then decides whether or not to act based on if it can operate on that type. Are there any simple ways to do this? I figured this would be fairly simple to do with generics, b...
I've recently asked a question on StackoverFlow about the MVC: Can the MVC Design Pattern / Architectural pattern be used in Desktop Application Development? Based on the answer provided I started research on how this would be implemented in a Windows form Application. I came upon the following CodeProject article: http://www.codeprojec...
Dear Stack, Is it possible, using an Observer, to observe the creation of JOIN records? For example, you have a User Model that has_and_belongs_to_many Book Models. Is it possible to monitor books_users records as they are created or deleted or must I have a BookUser model to do this? Example of what I want to observe: User.books <<...
Hi guys, I've been using javascript to do lightweight functionality on sites for years - DOM manipulation etc - but just now im beginning to investigate using it to do a lot more of the heavy lifting (in combo with PHP). I've only just started getting into OO JS, and im still trying to get my head around the best-practices and design pa...
Hi, I am having problems with implementing Observer pattern in my project. The project has to be made as MVC in C#, like a Windows application. In my domain model I have for example Country class and Country repository. I have a Country controller and views for seeing all countries(a list on a form), adding new country, and editing exis...
Hi, I'm building an app in PHP and I'm using the data mapper pattern for my DB access. I was considering using the Observer pattern to have all my mappers observe the entities they create, so that they can automatically save any changes back to the database without me having to parse them back manually. I was just wondering if this was...
Hello, I'm looking for a design pattern that would fit my application design. My application processes large amounts of data and produces some graphs. Data processing (fetching from files, CPU intensive calculations) and graph operations (drawing, updating) are done in seperate threads. Graph can be scrolled - in this case new data...
I've got the following (simplified): interface IFindFilesObserver { void OnFoundFile(FileInfo fileInfo); void OnFoundDirectory(DirectoryInfo directoryInfo); } class FindFiles { IFindFilesObserver _observer; // ... } ...and I'm conflicted. This is basically what I would have written in C++, but C# has events. Should I...
Say you have the following java bean: public class MyBean { private List<String> names = new ArrayList<String>(); public void addName(String name) { names.add(name); fireNamesPropertyChange(name); } } How would you normally implement a property change event for a collection? Do you try and use the inde...
Seam will fire different kinds of events that relate to particular scopes, tasks, or processes and appends the name of the scope, task or process to the end of the event. How do I listen to all the events of a type? E.g. for any <name> I'd like to listen to events such as these: org.jboss.seam.createProcess.<name> — called when the p...
I'm writing an App using WCF where clients subscribe to a server and then updates get pushed back to the clients. The subscribers subscribe to the server using a DuplexPipeChannel calling a Subscribe() method on the server. The server maintains a List<> of subscribers and when there is data to push out to the subscribers it calls a Pus...
I come from a C# background, and have just started programming in Ruby. The thing is, that I need to know how I can raise events in my classes so that various observers can be triggered when things need to happen. The problem is the books I have on Ruby don't even mention events, let alone provide examples. Is anyone able to help me? ...
Hi, i'm looking for a C++ replacement of the Python PubSub Library in which i don't have to connect a signal with a slot or so, but instead can register for a special Kind of messages, without knowing the object which can send it. ...
I'm using restful_authentication in my app. I'm creating a set of default users using a rake task, but every time I run the task an activation email is sent out because of the observer associated with my user model. I'm setting the activation fields when I create the users, so no activation is necessary. Anyone know of an easy way to...
Hi, I want to implement an Observer of a Model class which does not change the Model. Thus, it should be able to use a const-Reference to access the Model. But the Registering of the Observer prohibits this. Here is how the observer pattern is implemented in my Project: //Attributes of type Observable are used by classes that want ...
I've got a static class (DataFormSubject) that holds a generic List object, as follows: private static List<DataForm> dataForms = new List<DataForm>(); Other classes that rely on this list need to be told when the list is updated, so I created a custom event, and associated methods that could trigger when an item is added or removed, ...
Hi, I have a dropdown box in my GUI which shows the contents of an ArrayList in another class. New objects can be added to the ArrayList elsewhere in the GUI, so I need to know when it is updated, so I can refresh the dropdown menu. From what I can gather, my two options are to extend the ArrayList class to allow me to add my own change...