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  • Alternatives to the Singleton Design Pattern

    The Singleton Design Pattern is one of the simplest and most widely known design patterns in use in software development. However, despite its simplicity, it is very easy to get wrong and the consequences of its use even when properly implemented can outweigh its benefits. It turns out there are other ways to achieve the goals of the Singleton pattern which will often prove to be simpler, safer, and more maintainable.

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  • Importance of Corporate Logo Design

    You need to bind to certain basic principles that ensure that corporate logo design is professional and easy to remember and creates a great impact on viewers while successfully expressing the nature... [Author: Alan Smith - Web Design and Development - May 13, 2010]

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  • Architecting persistence (and other internal systems). Interfaces, composition, pure inheritance or centralization?

    - by Vandell
    Suppose that you need to implement persistence, I think that you're generally limited to four options (correct me if I'm wrong, please) Each persistant class: Should implement an interface (IPersistent) Contains a 'persist-me' object that is a specialized object (or class) that's made only to be used the class that contains it. Inherit from Persistent (a base class) Or you can create a gigantic class (or package) called Database and make your persistence logic there. What are the advantages and problems that can come from each of one? In a small (5kloc) and algorithmically (or organisationally) simple app what is probably the best option?

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  • Appropriate design / technologies to handle dynamic string formatting?

    - by Mark W
    recently I was tasked with implementing a way of adding support for versioning of hardware packet specifications to one of our libraries. First a bit of information about the project. We have a hardware library which has classes for each of the various commands we support sending to our hardware. These hardware modules are essentially just lights with a few buttons, and a 2 or 4 digit display. The packets typically follow the format {SOH}AADD{ETX}, where AA is our sentinel action code, and DD is the device ID. These packet specs are different from one command to the next obviously, and the different firmware versions we have support different specifications. For example, on version 1 an action code of 14 may have a spec of {SOH}AADDTEXT{ETX} which would be AA = 14 literal, DD = device ID, TEXT = literal text to display on the device. Then we come out with a revision with adds an extended byte(s) onto the end of the packet like this {SOH}AADDTEXTE{ETX}. Assume the TEXT field is fixed width for this example. We have now added a new field onto the end which could be used to say specify the color or flash rate of the text/buttons. Currently this java library only supports one version of the commands, the latest. In our hardware library we would have a class for this command, say a DisplayTextArgs.java. That class would have fields for the device ID, the text, and the extended byte. The command class would expose a method which generates the string ("{SOH}AADDTEXTE{ETX}") using the value from the class. In practice we would create the Args class as needed, populate the fields, call the method to get our packet string, then ship that down across the CAN. Some of our other commands specification can vary for the same command, on the same version, depending on some runtime state. For example, another command for version 1 may be {SOH}AA{ETX}, where this action code clears all of the modules behind a specific controller device of their text. We may overload this packet to have option fields with multiple meanings like {SOH}AAOC{ETX} where OC is literal text, which tells the controller to only clear text on a specific module type, and to leave the others alone, or the spec could also have an option format of {SOH}AADD{ETX} to clear the text off a a specific device. Currently, in the method which generates the packet string, we would evaluate fields on the args class to determine which spec we will be using when formatting the packet. For this example, it would be along the lines of: if m_DeviceID != null then use {SOH}AADD{ETX} else if m_ClearOCs == true then use {SOH}AAOC{EXT} else use {SOH}AA{ETX} I had considered using XML, or a database to store String.format format strings, which were linked to firmware version numbers in some table. We would load them up at startup, and pass in the version number of the hardwares firmware we are currently using (I can query the devices for their firmware version, but the version is not included in all packets as part of the spec). This breaks down pretty quickly because of the dynamic nature of how we select which version of the command to use. I then considered using a rule engine to possibly build out expressions which could be interpreted at runtume, to evaluate the args class's state, and from that select the appropriate format string to use, but my brief look at rule engines for java scared me away with its complexity. While it seems like it might be a viable solution, it seems overly complex. So this is why I am here. I wouldn't say design is my strongest skill, and im having trouble figuring out the best way to approach this problem. I probably wont be able to radically change the args classes, but if the trade off was good enough, I may be able to convince my boss that the change is appropriate. What I would like from the community is some feedback on some best practices / design methodologies / API or other resources which I could use to accomplish: Logic to determine which set of commands to use for a given firmware version Of those command, which version of each command to use (based on the args classes state) Keep the rules logic decoupled from the application so as to avoid needing releases for every firmware version Be simple enough so I don't need weeks of study and trial and error to implement effectively.

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  • Revamp Websites With Custom Design

    The concept of web design encompasses the task of developing hypertext or hypermedia content which a user can access through the World Wide Web. Through web design websites are created. The concept entails more on designing rather than development, i.e. taking care of the graphic elements, look and feel and other aesthetic feature. It is different from professional web development which often concentrates on the technical aspect of the website.

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  • Web Design Before The Style Sheet Language

    In today';s trends of website design, the use of style sheet languages such as CSS (Cascading Style Sheets) and XSL (Extensible StyleSheet Languages) are considered necessary to build a successful web... [Author: Margarette Mcbride - Web Design and Development - May 17, 2010]

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  • Web Design in Today's Economy

    Web Design in today's Economy In today's economy businesses are looking for cheaper ways to get their Web Design and Web Development needs met. This is not necessarily a bad thing, however with web sites you get what you pay for.

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  • CSS In The World Of Website Design

    Style sheet languages are computer languages which have now been heavily used in the Internet. It was introduced in the industry of website design when people sought many ways on how to avoid the use... [Author: Margarette Mcbride - Web Design and Development - May 06, 2010]

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  • SEO Web Design - A Worthwhile Investment?

    The last decade has seen an increased focus on SEO and SEO web design. With SEO a popular 'buzz' word amongst businesses of many different sizes some people may have begun to ask themselves how they could benefit from SEO web design.

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  • The Rise Of CSS In Web Design

    Style sheet languages were introduced in the market because of their capability to reduce the problems which are usually associated with the use of tables in website design. One of the most popular s... [Author: Margarette Mcbride - Web Design and Development - May 04, 2010]

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  • Passing data structures to different threads

    - by Robb
    I have an application that will be spawning multiple threads. However, I feel there might be an issue with threads accessing data that they shouldn't be. I'm relatively new to threading so bare with me. Here is the structure of the threaded application (sorry for the crudeness): MainThread / \ / \ / \ Thread A Thread B / \ / \ / \ / \ / \ / \ Thread A_1 Thread A_2 Thread B_1 Thread B_2 Under each lettered thread (which could be many), there will only be two threads and they are fired of sequentially. The issue i'm having is I'm not entirely sure how to pass in a datastructure into these threads. So, the datastructure is created in MainThread, will be modified in the lettered thread (Thread A, etc) specific to that thread and then a member variable from that datastructure is sent to Letter_Numbered threads. Currently, the lettered thread class has a member variable and when the class is constructed, the datastructure from mainthread is passed in by reference, invoking the copy constructor so the lettered thread has it's own copy to play with. The lettered_numbered thread simply takes in a string variable from the data structure within the lettered thread. My question is, is this accceptable? Is there a much better way to ensure each lettered thread gets its own data structure to play with? Sorry for the somewhat poor explanation, please leave comments and i'll try to clarify.

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  • how to share a variable between two threads

    - by prmatta
    I just inherited some code, two threads within this code need to perform a system task. One thread should do the system task before the other thread. They should not be performing the system task together. The two threads do not have references to each other. Now, I know I can use some sort of a semaphore to achieve this. But my question is what is the right way to get both threads to access this semaphore. I could create a static variable/method a new class : public class SharedSemaphore { private static Semaphore s = new Semaphore (1, true); public static void performSystemTask () { s.acquire(); } public static void donePerformingSystemTask() { s.release(); } } This would work (right?) but this doesn't seem like the right thing to do. Because, the threads now have access to a semaphore, without ever having a reference to it. This sort of thing doesn't seem like a good programming practice. Am I wrong?

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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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  • Protocol specification in XML

    - by Mathijs
    Is there a way to specify a packet-based protocol in XML, so (de)serialization can happen automatically? The context is as follows. I have a device that communicates through a serial port. It sends and receives a byte stream consisting of 'packets'. A packet is a collection of elementary data types and (sometimes) other packets. Some elements of packets are conditional; their inclusion depends on earlier elements. I have a C# application that communicates with this device. Naturally, I don't want to work on a byte-level throughout my application; I want to separate the protocol from my application code. Therefore I need to translate the byte stream to structures (classes). Currently I have implemented the protocol in C# by defining a class for each packet. These classes define the order and type of elements for each packet. Making class members conditional is difficult, so protocol information ends up in functions. I imagine XML that looks like this (note that my experience designing XML is limited): <packet> <field name="Author" type="int32" /> <field name="Nickname" type="bytes" size="4"> <condition type="range"> <field>Author</field> <min>3</min> <max>6</min> </condition> </field> </packet> .NET has something called a 'binary serializer', but I don't think that's what I'm looking for. Is there a way to separate protocol and code, even if packets 'include' other packets and have conditional elements?

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  • Is it a good object-oriented-design practice to send a pointer to private data to another class?

    - by Denis
    Hello everyone, There is well known recommendation not to include into class interface method that returns a pointer (or a reference) to private data of the class. But what do you think about public method of a class that sends to another class a pointer to the private data of the first one. For example: class A { public: void fA(void) {_b.fB(&_var)}; private: B _b; int _var; }; I think that it is some sort of data hiding damage: the private data define state of their own class, so why should one class delegate changes of its own state to another one? What do you think? Denis

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  • Factory pattern vs ease-of-use?

    - by Curtis White
    Background, I am extending the ASP.NET Membership with custom classes and extra tables. The ASP.NET MembershipUser has a protected constructor and a public method to read the data from the database. I have extended the database structure with custom tables and associated classes. Instead of using a static method to create a new member, as in the original API: I allow the code to instantiate a simple object and fill the data because there are several entities. Original Pattern #1 Protected constructor > static CreateUser(string mydata, string, mydata, ...) > User.Data = mydata; > User.Update() My Preferred Pattern #2 Public constructor > newUser = new MembershipUser(); > newUser.data = ... > newUser.ComplextObject.Data = ... > newUser.Insert() > newUser.Load(string key) I find pattern #2 to be easier and more natural to use. But method #1 is more atomic and ensured to contain proper data. I'd like to hear any opinions on pros/cons. The problem in my mind is that I prefer a simple CRUD/object but I am, also, trying to utilize the underlying API. These methods do not match completely. For example, the API has methods, like UnlockUser() and a readonly property for the IsLockedOut

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  • Designing a state machine in C++

    - by skyeagle
    I have a little problem that involves modelling a state machine. I have managed to do a little bit of knowledge engineering and 'reverse engineer' a set of primitive deterministic rules that determine state as well as state transitions. I would like to know what the best practises are regarding: How to rigorously test my states and state transitions to make sure that the system cannot end up in an undeetermined state. How to enforce state transition requirements (for example, it should be impossible to go directly from stateFoo to StateFooBar, i.e. to embue each state with 'knowlege' about the states it can transition to. Ideally, I would like to use clean, pattern based design, with templates wherever possible. I do need somewhere to start though and I would be grateful for any pointers (no pun intended), that are sent my way.

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  • F#: Define an abstract class that inherits an infterface, but does not implement it

    - by akaphenom
    I owuld like to define an abstract class that inerhits from UserControl and my own Interface IUriProvider, but doesn't implement it. The goal is to be able to define pages (for silverlight) that implement UserControl but also provide their own Uri's (and then stick them in a list / array and deal with them as a set: type IUriProvider = interface abstract member uriString: String ; abstract member Uri : unit -> System.Uri ; end type UriUserControl() as this = inherit IUriProvider with abstract member uriString: String ; inherit UserControl() Also the Uri in the definition - I would like to implement as a property getter - and am having issues with that as well. this does not compile type IUriProvider = interface abstract member uriString: String with get; end Thank you...

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  • overflow-x AND Middle Mouse Button Moving

    - by Rad The Mad
    My Page is 980px in Width, but I have a few design elements (which belong with the background). I positioned them with position: absolute;. This creates a horizontal scrollbar for those who have a =< 1024 resolution. I disabled that scrollbar with overflow-x:hidden on (and for IE7 and etc). However, when I hold my middle mouse button,(i think this applies to laptop touchpads as well) it let's me move around to the right, is it possible to fix this with anything? (javascript, css)? Tested this issues in Chrome, IE, Firefox.

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  • What patterns exist for web application development?

    - by DaveDev
    I understand that MVC & MVP are design patterns that are commonly used for web development, as well as ASP.NET WebForms (more of an anti-pattern, really!). What other patterns are used in web application development? I'm not necessarily saying I want to learn/use new patterns just to be different - I do believe there's a lot of value in taking the conventional route - but I think it's good to know what else is out there to be able to properly understand what I'm currently working with. Thanks.

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  • How to apply Abstract Factory Pattern ???

    - by Amit
    I am new to Design Pattern and I have a scenario here... and not sure as how to implement the pattern ... We have multiple vendors Philips, Onida... Each vendor (philips, onida...) may have different type of product i.e. Plasma or Normal TV I want specific product of each vendor using Abstract Factory Pattern... Thanks in advance for any help... My implementation so far... public enum TvType { Samsung = 0,LG = 1,Philips = 2, Sony = 3 } public enum Product { Plasma = 0,NormalTV = 1 } concrete class of each vendor.... that returns each product and also the interface that contains ProductInfo i.e. if Vendor is ... then it must have this product....

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  • How to implement "drag n drop" user interface on website?

    - by Nikkeloodeni
    Hello, I was wondering what would be the best way to implement some kind of "drag n drop" user interface? What i mean is that there would be one main page and every link click (eg. other sections like about, gallery, contact form) would open a new drag n drop element on top of that main page. Something like windows desktop where you can move your application windows around the screen. Would it be best to call different functions with AJAX when a link is clicked? Like "gallery" link would call gallery-function and retrieve dynamically generated contents of that "window" with AJAX call and then just load that stuff on some div? Or would some other type of approach suit better for this? I hope I was able to explain this clearly enough. I'm looking for a proper "design pattern" to implement this. All suggestions are wellcome! :)

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