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• Application wide messaging... without singletons?

  - by StormianRootSolver

  So, I want to go for a more Singleton - less design in the future. However, there seem to be a lot of tasks in an application that can't be done in meaningful way without singletons. I call them "application wide services", but they also fall into the same category as the cross cutting concerns, which I usually fix via AOP. Lets take an example: I want an application wide message queue that dispatches messages to components, every component can subscribe and publish there, it's a very nice multicast thing. The message queue and dispatching system are usually a (rather short) singleton class, which is very easy to implement in, say, C#. You can even use double dispatching and utilize message type metadata and the like, it's all so easy to do, it's almost trivial. However, having singletons is not really "object oriented design" (it introduces global variables) and it makes testing harder. Do you have any ideas? I'm asking this question because I'm willing to learn more about this topic, a LOT more. :-)

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• Static assembly initialization

  - by ph0enix

  I'm attempting to develop an Interceptor framework (in C#) where I can simply implement some interfaces, and through the use of some static initialization, register all my Interceptors with a common Dispatcher to be invoked at a later time. The problem lies in the fact that my Interceptor implementations are never actually referenced by my application so the static constructors never get called, and as a result, the Interceptors are never registered. If possible, I would like to keep all references to my Interceptor libraries out of my application, as this is my way of (hopefully) enforcing loose coupling across different modules. Hopefully this makes some sense. Let me know if there's anything I can clarify... Does anyone have any ideas, or perhaps a better way to go about implementing my Interceptor pattern? TIA, Jeremy

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• How to implement the disposable pattern in a class that inherits from another disposable class?

  - by TheRHCP

  Hi, I often used the disposable pattern in simple classes that referenced small amount of resources, but I never had to implement this pattern on a class that inherits from another disposable class and I am starting to be a bit confused in how to free the whole resources. I start with a little sample code: public class Tracer : IDisposable { bool disposed; FileStream fileStream; public Tracer() { //Some fileStream initialization } public void Dispose() { this.Dispose(true); GC.SuppressFinalize(this); } protected virtual void Dispose(bool disposing) { if (!disposed) { if (disposing) { if (fileStream != null) { fileStream.Dispose(); } } disposed = true; } } } public class ServiceWrapper : Tracer { bool disposed; ServiceHost serviceHost; //Some properties public ServiceWrapper () { //Some serviceHost initialization } //protected override void Dispose(bool disposing) //{ // if (!disposed) // { // if (disposing) // { // if (serviceHost != null) // { // serviceHost.Close(); // } // } // disposed = true; // } //} } My real question is: how to implement the disposable pattern inside my ServiceWrapper class to be sure that when I will dispose an instance of it, it will dispose resources in both inherited and base class? Thanks.

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• Dynamic Object Initialization In JavaScript (just like PHP Reflection allows)?

  - by Gcoop

  Hi All, Using Reflection in PHP I can dynamically create a object like so $target = 'core_domain_Person'; $reflect = new ReflectionClass($target); $obj = $reflect->newInstance(); I would like to replicate this same concept in JavaScript is there a way to do this out of the box? Or is there a way to replicate what Reflection is doing?

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• c++ design question: Can i query the base classes to find the number of derived classes satisfying a

  - by vivekeviv

  I have a piece of code like this class Base { public: Base(bool _active) { active = _active; } void Configure(); void Set Active(bool _active); private: bool active; }; class Derived1 : public Base { public: Derived1(bool active):Base(active){} }; similarly Derived 2 and Derived 3 Now if i call derived1Object.Configure, i need to check how many of the derived1Obj, derived2Obj,derived3Obj is active. Should i add this in the "Base" class like a function say, GetNumberOfActive()? And If the implementation is like this: class Imp { public: void Configure() { //Code instantiating a particular Derived1/2/3 Object int GetNumberOfActiveDerivedObj(); baseRef.Configure(int numberOfActiveDerivedClasses); } prive: Derived1 dObj1(true); Derived2 dObj2(false); Derived3 dObj3(true); }; should i calculate the numberOfActive Derived Objects in Imp Class? THanks

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• What's Advantage of IoC

  - by Kurt Liu

  What is different between Inversion Of Control pattern and I rewrite old class while keeping same method name and parameter? I just can not see what's advantage of IoC.

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• benefit os having a factory for object creation?

  - by ajsie

  im trying to understand the factory design pattern. i dont understand why it's good to have a middleman between the client and the product (object that the client wants). example with no factory: $mac = new Mac(); example with a factory: $appleStore = new AppleStore(); $mac = $appleStore->getProduct('mac'); how does the factory pattern decouple the client from the product? could someone give an example of a future code change that will impact on example 1 negative, but positive in example 2 so i understand the importance of decoupling? thanks

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• How to design the application to conform to the n-tier architecture? (Winform sample in .net with li

  - by AlexRednic

  Rather a simple question. But the implications are vast. Over the last few weeks I've been reading a lot of material about n-tier architecture and it's implementation in the .NET world. The problem is I couldn't find a relevant sample for Winforms with Linq (linq is the way to go for BLL right?). How did you guys manage to grasp the n-tier concept? Books, articles, relevant samples etc.

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• Design pattern for loading multiple message types

  - by lukem00

  As I was looking through SO I came across a question about handling multiple message types. My concern is - how do I load such a message in a neat way? I decided to have a separate class with a method which loads one message each time it's invoked. This method should create a new instance of a concrete message type (say AlphaMessage, BetaMessage, GammaMessage, etc.) and return it as a Message. class MessageLoader { public Message Load() { // ... } } The code inside the method is something which looks really awful to me and I would very much like to refactor it/get rid of it: Message msg = Message.Load(...); // load yourself from whatever source if (msg.Type == MessageType.Alpha) return new AlphaMessage(msg); if (msg.Type == MessageType.Beta) return new BetaMessage(msg); // ... In fact, if the whole design looks just too messy and you guys have a better solution, I'm ready to restructure the whole thing. If my description is too chaotic, please let me know what it's missing and I shall edit the question. Thank you all.

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• Exception handling pattern

  - by treefrog

  It is a common pattern I see where the error codes associated with an exception are stored as Static final ints. when the exception is created to be thrown, it is constructed with one of these codes along with an error message. This results in the method that is going to catch it having to look at the code and then decide on a course of action. The alternative seems to be- declare a class for EVERY exception error case Is there a middle ground ? what is the recommended method ?

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• What is it called when an object member returns the object, enabling you to string method calls?

  - by thepearson

  Perhaps I'm just not using the right Google-age. But I am trying to remember what the term is for when you return the object from one of it members to enable you to do something similar: class obj { obj function method() { return this } } obj->method()->method()->method()->method() I used to know this but it has totally escaped me.

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• Structuring iPhone/iPad application views

  - by Mark

  I have an idea about an application that I want to build and Im new to iPhone/iPad development (but not new to development in other languages/frameworks such as .NET and Java). I want to layout some views on the screen so that they animate (slide in) from different directions into their places. The question is about the strucuture of the application, if I have say 4 rectanglular areas on the screen that contain business data, such as contacts (name, photo, etc...) and they all take up different widths of the screen (say the first contact takes up one row of the screen, but the next 2 take up half the width of the next row each, and so on). Should I create a custom view for the different sized contact views, (i.e. LargeCustomView and SmallCustomView, and any other special type that I make) or should it all be one type, say, CustomerDetailsView which could be stretched to fit at design time? Also, if there were, say, 3 different instances of the same custom view on the one screen, are there 3 instances of the view controller also? Im a little confused about powering the data behind a view, can someone shed some light on this for me? Do I just set the properties (say an instance variable ContactForView) on the view controller for each instance? Thanks for any help you can give Cheers, Mark

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• How would Unit of Work apply in a web application?

  - by fig-gnuton

  How would Unit of Work apply in an ajax-heavy web application, where client-side changes may not always be immediately persisted to the server?

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• What is the best way to restore(rollback) data in an application to a specified state(date) ?

  - by panzerschreck

  Hello, An example would set the context right, the example below captures the various states of the entity, which needs to be reverted(rolled back) . State 1 - Recorded on 01-Mar-2010 Column1 Column2 Data1 0.56 State 2 - Recorded on 02-Mar-2010 Column1 Column2 Data1 0.57 State 3 - Recorded on 03-Mar-2010 Column1 Column2 Data1 0.58 User notices that state3 is not what he intended to be in, decides to revert back to state2. One approach that I can think of, without modifying the entity is via "auditing" all the inserts/updates, as below, the rollback information captures the data just before the updates/modifications on the entity, so that it can be applied in an order when you need to revert.Please note that changing the entity's schema, is not an option. Rollback - R1 recorded on 01-Mar-2010 Column1 Column2 Data1 0.56 Rollback - R2 Recorded on 02-Mar-2010 Column1 Column2 Data1 0.56 Rollback - R3 Recorded on 03-Mar-2010 Column1 Column2 Data1 0.57 So, to get to state2 , we would start with rollback information R1,apply R2 onto it. Is there a better approach to achieve this ? Thanks for your time.

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• How much to put in a Repository class?

  - by chobo

  When using the repository pattern is it recommended to have one Repository class for each database table? Would I also map one service layer class to one repository class. I'm having a hard time trying to understand how much stuff one repository or service layer class should have. Thanks!

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• Many-to-many relationship in oop

  - by Manu

  what is best way to model many-to-many relationship? lets say we have a two classes , Team and Player any given Player can be in multiple Team s any Team can have as many Player s as they like I like to call methods like playerX.getTeamList() to get the list of all the Team s he/she is in teamY.getPlayerList() to get the list of all the Player s in the team (or have some other way to do this effectively) I can think of two ways of doing this , but they just don't feels like good oop pattens. can you think of any good ways , perhaps a design patten ?

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• How should nested components interact with model in a GUI application?

  - by fig-gnuton

  Broad design/architecture question. If you have nested components in a GUI, what's the most common way for those components to interact with data? For example, let's say a component receives a click on one of its buttons to save data. Should the save request be delegated up that component's ancestors, with the uppermost ancestor ultimately passing the request to a controller? Or are models/datastores in a GUI application typically singletons, so that a component at any level of a hierarchy can directly get/set data? Or is a controller injected as a dependency down the hierarchy of components, so that any given component is only one intermediary away from the datastore/model?

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• Where does the query language sit within the MVC pattern?

  - by weesilmania

  I'd assume that since the query language sits within the controller (typically) that it belongs to that component, but if I play devil's advocate I'd argue that the query language is execute within the domain of the model, and is tightly coupled to that component so it might also be a part of it. Anyone know the answer? Is there a straight answer or is it technology specific?

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• does anyone see any issues with this thread pattern?

  - by prmatta

  Here is a simple thread pattern that I use when writing a class that needs just one thread, and needs to a specific task. The usual requirements for such a class are that it should be startable, stopable and restartable. Does anyone see any issues with this pattern that I use? public class MyThread implements Runnable { private boolean _exit = false; private Thread _thread = null; public void start () { if (_thread == null) { _thread = new Thread(this, "MyThread"); _thread.start(); } } public void run () { while (_exit) { //do something } } public void stop () { _exit = true; if (_thread != null) { _thread.interrupt(); _thread = null; } } } I am looking for comments around if I am missing something, or if there is a better way to write this.

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• set width height by a set a parameter in html

  - by Richa Media and services

  i need to set a image at 128*128px on a html page. i know the way width="128px" height="128px" but are i can do it by write a parameter on image like param="128px" then he set width and height 128px;

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• what is main focus for a developer when coding?

  - by ajsie

  i read a lot of books about how to code right and usually the are talking about all these techniques from a point of view i can't understand. eg. lets consider the singleton pattern. i'm restricting so the class can only be instantiated once. but since it's only me creating the application, if i know that the class only should be instantiated once, then why would i create it a second time? i feel like missing the big picture. what is my main goal when coding an application? how should i think? thanks

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• How can I achieve this kind of relationship (inheritance, composition, something else)?

  - by Tim

  I would like to set up a foundation of classes for an application, two of which are person and student. A person may or may not be a student and a student is always a person. The fact that a student “is a” person led me to try inheritance, but I can't see how to make it work in the case where I have a DAO that returns an instance of person and I then want to determine if that person is a student and call student related methods for it. class Person { private $_firstName; public function isStudent() { // figure out if this person is a student return true; // (or false) } } class Student extends Person { private $_gpa; public function getGpa() { // do something to retrieve this student's gpa return 4.0; // (or whatever it is) } } class SomeDaoThatReturnsPersonInstances { public function find() { return new Person(); } } $myPerson = SomeDaoThatReturnsPersonInstances::find(); if($myPerson->isStudent()) { echo 'My person\'s GPA is: ', $myPerson->getGpa(); } This obviously doesn't work, but what is the best way to achieve this effect? Composition doesn't sond right in my mind because a person does not “have a” student. I'm not looking for a solution necessarily but maybe just a term or phrase to search for. Since I'm not really sure what to call what I'm trying to do, I haven't had much luck. Thank you!

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• Methods calling other methods in the same class

  - by dotnetdev

  Hi, In class design, is it a bad habit if one method calls another method in the same class (For example, 3 methods call 1 method in the same class). Thanks

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• Sequencing ajax requests

  - by Scott Evernden

  I find I sometimes need to iterate some collection and make an ajax call for each element. I want each call to return before moving to the next element so that I don't blast the server with requests - which often leads to other issues. And I don't want to set async to false and freeze the browser. Usually this involves setting up some kind of iterator context that i step thru upon each success callback. I think there must be a cleaner simpler way? Does anyone have a clever design pattern for how to neatly work thru a collection making ajax calls for each item?

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• incapsulation of a code inmatlab

  - by user531225

  my code is pathname=uigetdir; filename=uigetfile('*.txt','choose a file name.'); data=importdata(filename); element= (data.data(:,10)); in_array=element; pattern= [1 3]; locations = cell(1, numel(pattern)); for p = 1:(numel(pattern)) locations{p} = find(in_array == pattern(p)); end idx2 = []; for p = 1:numel(locations{1}) start_value = locations{1}(p); for q = 2:numel(locations) found = true; if (~any((start_value + q - 1) == locations{q})) found = false; break; end end if (found) idx2(end + 1) = locations{1}(p); end end [m2,n2]=size(idx2) res_name= {'one' 'two'}; res=[n n2]; In this code I finding a pattern in one of the column of my data file and counting how many times it's repeated. I have like 200 files that I want to do the same with them but unfotunatlly I'm stuck. this is what I have added so far pathname=uigetdir; files=dir('*.txt'); for k=1:length(files) filename=files(k).name; data(k)=importdata(files(k).name); element{k}=data(1,k).data(:,20); in_array=element;pattern= [1 3]; locations = cell(1, numel(pattern)); for p = 1:(numel(pattern)) locations{p} = find(in_array{k}== pattern(p)); end idx2{k} = []; how can I continue this code..??

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