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  • Question about factory classes

    - by devoured elysium
    Currently I have created a ABCFactory class that has a single method creating ABC objects. Now that I think of it, maybe instead of having a factory, I could just make a static method in my ABC Method. What are the pro's and con's on making this change? Will it not lead to the same? I don't foresee having other classes inherit ABC, but one never knows! Thanks

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  • Visitor Pattern can be replaced with Callback functions?

    - by getit
    Is there any significant benefit to using either technique? In case there are variations, the Visitor Pattern I mean is this: http://en.wikipedia.org/wiki/Visitor_pattern And below is an example of using a delegate to achieve the same effect (at least I think it is the same) Say there is a collection of nested elements: Schools contain Departments which contain Students Instead of using the Visitor pattern to perform something on each collection item, why not use a simple callback (Action delegate in C#) Say something like this class Department { List Students; } class School { List Departments; VisitStudents(Action<Student> actionDelegate) { foreach(var dep in this.Departments) { foreach(var stu in dep.Students) { actionDelegate(stu); } } } } School A = new School(); ...//populate collections A.Visit((student)=> { ...Do Something with student... }); *EDIT Example with delegate accepting multiple params Say I wanted to pass both the student and department, I could modify the Action definition like so: Action class School { List Departments; VisitStudents(Action<Student, Department> actionDelegate, Action<Department> d2) { foreach(var dep in this.Departments) { d2(dep); //This performs a different process. //Using Visitor pattern would avoid having to keep adding new delegates. //This looks like the main benefit so far foreach(var stu in dep.Students) { actionDelegate(stu, dep); } } } }

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  • wpf command pattern

    - by evan
    I have a wpf gui which displays a list of information in separate window and in a separate thread from the main application. As the user performs actions in the main window the side window is updated. (For example if you clicked page down in the main window a listbox in the side window would page down). Right now the architecture for this application feels very messy and I'm sure there is a cleaner way to do it. It looks like this: Main Window contains a singleton SideWindowControl which communicates with an instance of the SideWindowDisplay using events - so, for example, the pagedown button would work like: 1) the event handler of the button on the main window calls SideWindowControl.PageDown() 2) in the PageDown() function a event is created and thrown. 3) finally the gui, ShowSideWindowDisplay is subscribing to the SideWindowControl.Actions event handles the event and actually scrolls the listbox down - note because it is in a different thread it has to do that by running the command via Dispatcher.Invoke() This just seems like a very messy way to this and there must be a clearer way (The only part that can't change is that the main window and the side window must be on different threads). Perhaps using WPF commands? I'd really appreciate any suggestions!! Thanks

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  • Unit Testing User Interface. What is an effective way ?

    - by pierocampanelli
    I have an accounting & payroll client/server application where there are several input form with complex data validation rules. I am finding an effective way to perform unit testing of user interface. For complex validation rules I mean: "Disable button X if I Insert a value in textfield Y" "Enable a combobox if I insert a value in a textfield" ...... ...... Most promising pattern i have found is suggested by M. Fowler (http://martinfowler.com/eaaDev/ModelViewPresenter.html). Have you any experience about Unit Testing of User Interface? As technology stack I am using: .NET 3.5 & Windows Forms Widget Library.

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  • What is so bad about Singletons

    - by Ewan Makepeace
    The Singleton pattern is a fully paid up member of the GoF Patterns Book but lately seems rather orphaned by the developer world. I still use quite a lot of singletons, especially for Factory classes, and while you have to be a bit careful about multithreading issues (like any class actually) fail to see why they are so awful. This site especially seems to assume that everyone agrees that Singletons are evil. Why?

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  • What are the differences between enterprise software/architecture patterns and open source software?

    - by Jeffrey
    I am mainly a business app developer and I hear terms like CQRS, ServiceBus, SOA, DDD, BDD, AOP a lot. My question is that do these patterns/practices exist only in the "enterprise" world? In contract to the enterprise world is the open source community. Highly trafficked sites like Digg, LiveJournal whenever there is an article mentioning about how they built/scaled their sites all I am hearing is what open source software (Memcached, NoSQL) they used in order to scale/simplify the way they tackle software problems and they rarely mention those above terms. Is it because they are not as sophisticated as those of enterprise level software (I doubt it)? Or are people just making up those terms/practices/patterns in order to keep them jobs? Or am I confusing myself with differences between software development and internet website scaling?

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  • Element Content Versus Attribute for Simple XML Value

    - by MB
    I know the elements versus attributes debate has come up many times here and elsewhere (e.g. here, here, here, here, and here) but I haven't seen much discussion of elements versus attributes for simple property values. So which of the following approaches do you think is better for storing a simple value? A: Value in Element Content: <TotalCount>553</TotalCount> <CelsiusTemperature>23.5</CelsiusTemperature> <SingleDayPeriod>2010-05-29</SingleDayPeriod> <ZipCodeLocation>12203</ZipCodeLocation> or B: Value in Attribute: <TotalCount value="553"/> <CelsiusTemperature value="23.5"/> <SingleDayPeriod day="2010-05-29"/> <ZipCodeLocation code="12203"/> I suspect that putting the value in the element content (A) might look a little more familiar to most folks (though I'm not sure about that). Putting the value in an attribute (B) might use less characters, but that depends on the length of the element and attribute names. Putting the value in an attribute (B) might be more extensible, because you could potentially include all sorts of extra information as nested elements. Whereas, by putting the value inside the element content (A), you're restricting extensibility to adding more attributes. But then extensibility often isn't a concern for really simple properties - sometimes you know that you'll never need to add additional data. Bottom line might be that it simply doesn't matter, but it would still be great to hear some thoughts and see some votes for the two options.

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  • Database schema for Product Properties

    - by Chemosh
    As so many people I'm looking for a Products /Product Properties database schema. I'm using Ruby on Rails and (Thinking) Sphinx for faceted searches. Requirements: Adding new product types and their options should not require a change to the database schema Support faceted searches using Sphinx. Solutions I've come across: (See Bill Karwin's answer) Option 1: Single Table Inheritance Not an option really. The table would contain way to many columns. Option 2: Class Table Inheritance Ruby on Rails caches the database schema on start-up which means a restart whenever a new type of product is introduced. If you have a size able product catalog this could mean hundreds of tables. Option 3: Serialized LOB Kills being able to do faceted searches without heavy application logic. Option 4: Entity-Attribute-Value For testing purposes, EAV worked fine. However it could quickly become a mess and a maintenance hell as you add more and more options (e.g. when an option increase the prices or delivery time). What option should I go with? What other solutions are out there? Is there a silver bullet (ha) I overlooked?

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  • Brilliant features of C++

    - by John
    (Following Features to remove from C++ and Desired features for C++, I thought why not complete the trio...) What C++ features would you not change? What features are elegantly and brilliantly implemented and still look better than other popular languages?

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  • Am I trying to Implement Multiple Inheritance. How can I do this.

    - by Shantanu Gupta
    I have created a class say A which has some functions defined as protected. Now Class B inherits A and class C inherits B. Class A has private default constructor and protected parameterized constructor. I want Class B to be able to access all the protected functions defined in Class A but class C can have access on some of the functions only not all the functions and class C is inheriting class B. How can I restrict access to some of the functions of Class A from Class C ? EDIT: namespace Db { public Class A { private A(){} protected A(string con){assign this value} protected DataTable getTable(){return Table;} protected Sqlparameters setParameters(){return parameter;} } } namespace Data { public Class B:A { protected B():base("constring"){} protected DataTable output(){return getTable();} protected sqlparameter values(param IDataParameter[] parameter){} } } namespace Bsns { public Class C:B { protected C():base(){} protected DataTable show() {return values(setparameter());} } } EDIT I think what I am trying to do here is Multiple inheritance. Please check. Class A { //suppose 10 functions are declared } Class B:A { //5 functions declared which are using A's function in internal body } Class C:B { //using all functions of B but require only 4 functions of A to be accessible by C. }

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  • What information do you capture when your software crashes in the field?

    - by Russ
    I am working on rewriting my unexpected error handling process, and I would like to ask the community: What information do you capture both automatic, and manually, when software you have written crashes? Right now, I capture a few items, some of which are: Automatic: Name of app that crashed Version of app that crashed Stack trace Operating System version RAM used by the application Number of processors Screen shot: (Only on non-public applications) User name and contact information (from Active Directory) Manual: What context is the user in (i.e.: what company, tech support call number, RA number, etc...) When did the user expect to happen? (Typical response: "Not to crash”) Steps to reproduce. What other bits of information do you capture that helps you discover the true cause of an applications problem, especially given that most users simply mash the keyboard when asked to tell you what happened. For the record I’m using C#, WPF and .NET version 4, but I don’t necessarily want to limit myself to those. Related: http://stackoverflow.com/questions/1226671/what-to-collect-information-when-software-crashes Related: http://stackoverflow.com/questions/701596/what-should-be-included-in-the-state-of-the-art-error-and-exception-handling-stra

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  • K-nearest neighbour with closed-loop dimensions

    - by Tomas
    Hi, I've got a K-nearest neighbour problem where some of the dimensions are closed loops. For example one is 'time of day' and I'm matching for similarity so 'very early morning' is close to 'late evening', you can't just make it a linear scale from 'very early morning' at one end to 'late evening' at the other. How can I represent this in the data model? Is there an established way to handle this or a way to work around it?

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  • @media queries - one rule overrides another?

    - by John
    I have multiple @media queries all working fine but as soon as i put in a higher max screen-width than 1024px the rules for the higher width gets applied to everything. @media screen and (max-width: 1400px) { #wrap { width: 72%; } } @media screen and (max-width: 1024px) { #slider h2 { width: 100%; } #slider img { margin: 60px 0.83333333333333% 0 2.08333333333333%; } .recent { width: 45.82%; margin: 10px 2.08333333333334% 0 1.875%; } } as you can see 1024px (and also the 800px max-width query) do not change the #wrap width and work fine. As soon as i add the 1400px max-width query it changes them to 72% for ALL sizes and does the same for any element - for instance if i set #slider img to have a margin of 40px it will show at ALL sizes even though it is only in the max-width of 1400px. Am i missing something really obvious? Been trying to work this out for the past 2 days! Thanks, John

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  • How to handle customers with multiple addresses in CakePHP

    - by Ryan
    I'm putting together a system to track customer orders. Each order will have three addresses; a Main contact address, a billing address and a shipping address. I do not want to have columns in my orders table for the three addresses, I'd like to reference them from a separate table and have some way to enumerate the entry so I can determine if the addressing is main, shipping or billing. Does it make sense to create a column in the address table for AddressType and enumerate that or create another table - AddressTypes - that defines the address enumeration and link to that table? I have found other questions that touch on this topic and that is where I've taken my model. The problem I'm having is taking that into the cakePHP convention. I've been struggling to internalize the direction OneToMany relationships are formed - the way the documentation states feels backwards to me. Any help would be appreciated, Thanks!

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  • Game logic dynamically extendable architecture implementation patterns

    - by Vlad
    When coding games there are a lot of cases when you need to inject your logic into existing class dynamically and without making unnecessary dependencies. For an example I have a Rabbit which can be affected by freeze ability so it can't jump. It could be implemented like this: class Rabbit { public bool CanJump { get; set; } void Jump() { if (!CanJump) return; ... } } But If I have more than one ability that can prevent it from jumping? I can't just set one property because some circumstances can be activated simultanously. Another solution? class Rabbit { public bool Frozen { get; set; } public bool InWater { get; set; } bool CanJump { get { return !Frozen && !InWater; } } } Bad. The Rabbit class can't know all the circumstances it can run into. Who knows what else will game designer want to add: may be an ability that changes gravity on an area? May be make a stack of bool values for CanJump property? No, because abilities can be deactivated not in that order in which they were activated. I need a way to seperate ability logic that prevent the Rabbit from jumping from the Rabbit itself. One possible solution for this is making special checking event: class Rabbit { class CheckJumpEventArgs : EventArgs { public bool Veto { get; set; } } public event EventHandler<CheckJumpEvent> OnCheckJump; void Jump() { var args = new CheckJumpEventArgs(); if (OnCheckJump != null) OnCheckJump(this, args); if (!args.Veto) return; ... } } But it's a lot of code! A real Rabbit class would have a lot of properties like this (health and speed attributes, etc). I'm thinking of borrowing something from MVVM pattern where you have all the properties and methods of an object implemented in a way where they can be easily extended from outside. Then I want to use it like this: class FreezeAbility { void ActivateAbility() { _rabbit.CanJump.Push(ReturnFalse); } void DeactivateAbility() { _rabbit.CanJump.Remove(ReturnFalse); } // should be implemented as instance member // so it can be "unsubscribed" bool ReturnFalse(bool previousValue) { return false; } } Is this approach good? What also should I consider? What are other suitable options and patterns? Any ready to use solutions? UPDATE The question is not about how to add different behaviors to an object dynamically but how its (or its behavior) implementation can be extended with external logic. I don't need to add a different behavior but I need a way to modify an exitsing one and I also need a possibiliity to undo changes.

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  • Are bad data issues that common?

    - by Water Cooler v2
    I've worked for clients that had a large number of distinct, small to mid-sized projects, each interacting with each other via properly defined interfaces to share data, but not reading and writing to the same database. Each had their own separate database, their own cache, their own file servers/system that they had dedicated access to, and so they never caused any problems. One of these clients is a mobile content vendor, so they're lucky in a way that they do not have to face the same problems that everyday business applications do. They can create all those separate compartments where their components happily live in isolation of the others. However, for many business applications, this is not possible. I've worked with a few clients, one of whose applications I am doing the production support for, where there are "bad data issues" on an hourly basis. Yeah, it's that crazy. Some data records from one of the instances (lower than production, of course) would have been run a couple of weeks ago, and caused some other user's data to get corrupted. And then, a data script will have to be written to fix this issue. And I've seen this happening so much with this client that I have to ask. I've seen this happening at a moderate rate with other clients, but this one just seems to be out of order. If you're working with business applications that share a large amount of data by reading and writing to/from the same database, are "bad data issues" that common in your environment?

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  • What technologies/tools do people use to implement live websites ?

    - by MadSeb
    Hi, I have the following situation: -I have a server A hooked up to a piece of hardware that sends values and information out of every second. Programs on the server machine can read these values. This server A is in a very remote location so Internet connection is very slow and not reliable but the connection does exist. Let's say it's a weather station in the Arctic. -Users from the home location want to monitorize the weather values somehow. Well, the users can use a remote desktop connection the server A but that would be too too slow. My idea is somehow to have a website on a web server (let's call the webserver - B and B is in a home location ) and make the server A connect to the server B and somehow send values and the web application reads the values and displays them....... but how to do such a system ?? I know I can use MySQL and have the server A connect to a SQL server on server B and send INSERT queries and have the web application running on server B constantly read from the SQL server but I think that would be way way too slow and I think there has to be a better solution. Any ideas ? BTW. The users should be able to send information to the weather station from the website as well ( so an ADMIN user should be allowed to shut down the weather station from the website or whatever) Best regards, MadSeb

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  • What's the proper way of importing option lists into an Android app?

    - by Scott
    I have been storing option lists for my Android app in a cloud table. For example, categories like "historical fiction","biography","science fiction", etc. I see the following pros and cons: Pro: I can make changes to the list without sending an app update to Google Play Not normalized - I can use the text in my other data tables instead of a reference ID Con: App needs to take time to download from the web each time (or at least check for changes) English only I believe the "proper" way to do this is the use the XML resource files. But I need to make sure the selection references correctly with my data. That is, my app needs to understand that "Poetry" and "Poesía" are the same thing. Is the correct thing to do: Forget about it since I'll never get to the point where I'm translating my app anyway Use a string-array and use the index (0...x) to know what the selection is Use a 2-dimensional string-array with a reference ID in the first column and the text in the second?

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  • Javascript libraries + JQuery plugins contradict? How to debug?

    - by Metafaniel
    This is somewhat a newbie question... I effort everyday to learn, so please understand ;) I'm not the very best expert, but I can do a decent job good looking and functional websites or web applications. My main tools are PHP5, HTML5, CSS2 y 3, a database (SQLite, MySQL) and Javascript and JQuery. I'm not an expert at all in Javascript. I often find interesting JQuery plugins or tutorials and try to mix them up to do the functionality needed. This time I'm mixing maybe too much plugins and js files from different sources. In fact, my app do what I want except for certain behaviors... There are no errors, everything looks fine, but the misbehavior persists. So maybe I need to specify a class I don't know about, or one contradicts another one from another plugin and I just can't understand, for example, why a <button type="button">DON'T submit</button> just submits the form... Anyway, my point is: Do you people know a way to debug this situations??? Is there a generic tool, suggestion, workflow or something to help me understand conflicts or omissions between libraries or plugins??? (Javascript libraries, my own Javascripts and JQuery plugins)??? I hope it is a way! THANKS A LOT FOR YOUR HELP AND COMPREHENSION! =)

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  • Process a batch of items, return an object to report on status

    - by Naeem Sarfraz
    I'm looking for a pattern (or good practice) for the following scenario: My function List<BatchItemResponse> Process(List<BatchItem> Data) {..} will process a list of data, and return info on where each item in the batch could be processed. struct BatchItemResponse { int BatchItemID; bool Processed; string Description; } Any thoughts? Is what I've proposed as good as it gets?

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  • Messaging strategies to connect different systems

    - by n002213f
    I have a system to handle Applications online and a different system to send SMS/Email notifications to applicants on completion using web services. I can't guarantee the availability of the SMS/Email gateway. Option 1 After an application is complete, place a message on a JMS queue. A Message Driven bean receives the message and make a call for the web service, if it fails leave the message on the queue. I suspect (please correct if incorrect) that if the gate way is offline the continuosly try to send the message which might use up valuable resources. Can the above option be refined are are there any other messaging strategies that can be used?

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