Questions tagged [observer-pattern]

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3
votes
1answer
215 views

Testing: Should I wrap system notifications and send my own?

In the current Cocoa app I'm working on, I've got an object, RecordScheduler, which responds to two types of notifications, "day did pass" and "quicksaving interval did pass". In both cases, the ...
2
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2answers
1k views

observer class as instance

Sometimes I read in observer-pattern descriptions, to make the constructor of a observer base class protected so the class will be abstract. but by making the constructor public (if even one is ...
10
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4answers
25k views

Which design pattern is more suitable for logging?

I should log some events in a program but as far as I know it would be better to keep the logging code outside the program because it is not about the real functionality of the program. So may you ...
1
vote
1answer
535 views

how to model a connection to a resource, with rudimentary event processing

For my simple MUD client I'm using Apache Telnet (no, not ssh). A mud client is a strange beast: Generally, a MUD client is a very basic telnet client that lacks VT100 terminal emulation and the ...
5
votes
1answer
4k views

Design patterns for multi-threaded messaging server

I'm designing an instant messaging server as a personal exercise to improve my understanding and application of multi-threading and design patterns in Java. I'm still designing, there's no code yet. ...
4
votes
1answer
622 views

Mutual observer pattern in Java

I want to improve my multi-threading and design pattern skills. As such I'm designing an Instant Messaging server. I'm writing the Server first. My plan so far is to have Client "Proxy" Classes to ...
4
votes
2answers
3k views

Publish/subscribe, observer pattern implementation question

I'm developing desktop application in java/swing. I have a component that is registered as a subscriber to many panels and gets messages (my custom event) from them. That component is something like ...
2
votes
3answers
568 views

Is the Observer pattern adequate for this kind of scenario?

I'm creating a simple game development framework with Ruby. There is a node system. A node is a game entity, and it has position. It can have children nodes (and one parent node). Children are always ...
2
votes
3answers
3k views

Automatically observing changes in database tables

currently I'm working on a project with the following setting: There is a proprietary application which performs transactions on a Microsoft Access database (which is actually stored as an .mdb file) ...
4
votes
4answers
706 views

Are Compiler Directives an Antipattern?

I'm working on a legacy system that has a helper class that is symbolically linked into many different .Net projects within a solution. The logic is riddled with compiler directives that change it's ...
1
vote
3answers
1k views

Is this Observer variant an improvement?

In a C++ code base I've been working on, they have a bunch of instances of the observer pattern, but it's a little different from the classical pattern. In the classic, the Observer is a specific ...
4
votes
2answers
2k views

Is there a design pattern for chained observers?

Several times, I've found myself in a situation where I want to add functionality to an existing Observer-Observable relationship. For example, let's say I have an Observable class called PriceFeed,...
9
votes
5answers
21k views

What are the advantages of the delegate pattern over the observer pattern?

In the delegate pattern, only one object can directly listen to another object's events. In the observer pattern, any number of objects can listen to a particular object's events. When designing a ...
-1
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2answers
473 views

Access functions from user control without events?

On some generic functions, it seems that accessing a function on mainform directly from the usercontrol is easier than raising an event. For example: A function on main form that displays one desired ...
1
vote
1answer
234 views

Observer pattern for unpredictable observation time

I have a situation where objects are created at unpredictable times. Some of these objects are created before an important event, some after. If the event already happened, I make the object execute ...
5
votes
4answers
2k views

Design Patterns for Coordinating Change Event Listeners

I've been working with the Observer pattern in JavaScript using various popular libraries for a number of years (YUI & jQuery). It's often that I need to observe a set of property value changes (e....
3
votes
3answers
356 views

Optimal communication pattern to update subscribers

What is the optimal way to update the subscriber's local model on changes C on a central model M? ( M + C -> M_c) The update can be done by the following methods: Publish the updated model M_c to ...
7
votes
2answers
2k views

Designing web-based plugin systems correctly so they don't waste as many resources?

Many CMS systems which rely on third parties for much of their code often build "plugin" or "hooks" systems to make it easy for developers to modify the codebase's actions without editing the core ...
10
votes
3answers
7k views

Observer pattern; knowing *what* changed?

I've created two abstract classes Subject and Observer that define a classic Observer pattern interface. I derive from them to implement the Observer pattern. An observer might look like this: void ...
9
votes
2answers
3k views

Observer pattern over HTTP and TCP/IP (Server-Client)

I have a server and many clients (around 50 clients) who connect to that server based on a web application, which is of course based on HTTP protocol, which in turn uses TCP/IP (correct me if I'm ...
4
votes
1answer
357 views

Would this be an effective use of the Subject/Observer pattern, or is there a better way?

TBH: I've never used an observer pattern. But it looks pretty useful for this situation: I'm developing a very simple strategy game. It involves two combatants who simultaneously bludgeon each ...