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• How can I get my business objects layer to use the management layer in their methods?

  - by Tom Pickles

  I have a solution in VS2010 with several projects, each making up a layer within my application. I have business entities which are currently objects with no methods, and I have a management layer which references the business entities layer in it's project. I now think I have designed my application poorly and would like to move methods from helper classes (which are in another layer) into methods I'll create within the business entities themselves. For example I have a VirtualMachine object, which uses a helper class to call a Reboot() method on it which passes the request to the management layer. The static manager class talks to an API that reboots the VM. I want to move the Reboot() method into the VirtualMachine object, but I will need to reference the management layer: public void Reboot() { VMManager.Reboot(this.Name); } So if I add a reference to my management project in my entities project, I get the circular dependency error, which is how it should be. How can I sort this situation out? Do I need to an yet another layer between the entity layer and the management layer? Or, should I just forget it and leave it as it is. The application works ok now, but I am concerned my design isn't particularly OOP centric and I would like to correct this.

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• Stateless singleton VS Static methods

  - by Sebastien Lorber

  Hey, Don't find any good answer to this simple question about helper/utils classes: Why would i create a singleton (stateless) rather than static methods? Why an object instance could be needed while the object has no state? Sometimes i really don't know what to use...

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• Using Remote Web Server to Initialize iPhone App

  - by Chris_K

  My iPhone app relies on a vendor's XML feed to provide data. But that feed is not locked down. The vendor could change the format of the XML at any time, although so far they've promised not to. Since I might want to tell my app to use a different URL for its data source, I'd like to set up a single "Command Central" Web page, on my own server, to direct the app to the correct data source. In other words, each time my app starts, in the background and unseen by the user, it would visit "http://www.myserver.com/iphoneapp_data_sources.xml" to retrieve the URL for retrieving data from my vendor. That way, if my vendor suddenly changes the exact URL or the XML feed that the app needs, I can update that Web page and ensure that all installations of the app are using the correct XML feed. Does anyone have any advice or examples showing this kind of approach? It seems as if this must be a common problem, but so far I haven't found a well-established design pattern that fits it.

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• Error handling inside or out of class?

  - by Rin

  Usually I do all what I can inside a class, in every method (try and catch). Am I doing it wrong? Recently I heard better way is handle error in program body... What is good habit?

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• Should I use a modified singleton design pattern that only allows one reference to its instance?

  - by Graham

  Hi, I have a class that would normally just generate factory objects, however this class should only used once throughout the program in once specifix place. What is the best design pattern to use in this instance? I throught that having a modified singleton design which only allows one reference to instance throughout the program would be the correct way to go. So only the first call to getInstance() returns the factory library. Is this a good or bad idea? Have I missed out another fundermental design pattern for solving this problem? Thanks for your help.

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• Have you ever derived a programming solution from nature?

  - by Ryu

  When you step back and look at ... the nature of animals, insects, plants and the problems they have organically solved perhaps even the nature and balance of the universe Have you ever been able to solve a problem by deriving an approach from nature? I've heard of Ant Colony Algorithms being able to optimize supply chain amongst other things. Also Fractal's being the "geometry of nature" have been applied to a wide range of problems. Now that spring is here again and the world is coming back to life I'm wondering if anybody has some experiences they can share. Thanks PS I would recommend watching the "Hunting the Hidden Dimension" Nova episode on fractals.

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• Refactoring Singleton Overuse

  - by drharris

  Today I had an epiphany, and it was that I was doing everything wrong. Some history: I inherited a C# application, which was really just a collection of static methods, a completely procedural mess of C# code. I refactored this the best I knew at the time, bringing in lots of post-college OOP knowledge. To make a long story short, many of the entities in code have turned out to be Singletons. Today I realized I needed 3 new classes, which would each follow the same Singleton pattern to match the rest of the software. If I keep tumbling down this slippery slope, eventually every class in my application will be Singleton, which will really be no logically different from the original group of static methods. I need help on rethinking this. I know about Dependency Injection, and that would generally be the strategy to use in breaking the Singleton curse. However, I have a few specific questions related to this refactoring, and all about best practices for doing so. How acceptable is the use of static variables to encapsulate configuration information? I have a brain block on using static, and I think it is due to an early OO class in college where the professor said static was bad. But, should I have to reconfigure the class every time I access it? When accessing hardware, is it ok to leave a static pointer to the addresses and variables needed, or should I continually perform Open() and Close() operations? Right now I have a single method acting as the controller. Specifically, I continually poll several external instruments (via hardware drivers) for data. Should this type of controller be the way to go, or should I spawn separate threads for each instrument at the program's startup? If the latter, how do I make this object oriented? Should I create classes called InstrumentAListener and InstrumentBListener? Or is there some standard way to approach this? Is there a better way to do global configuration? Right now I simply have Configuration.Instance.Foo sprinkled liberally throughout the code. Almost every class uses it, so perhaps keeping it as a Singleton makes sense. Any thoughts? A lot of my classes are things like SerialPortWriter or DataFileWriter, which must sit around waiting for this data to stream in. Since they are active the entire time, how should I arrange these in order to listen for the events generated when data comes in? Any other resources, books, or comments about how to get away from Singletons and other pattern overuse would be helpful.

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• What is the best practice for accessing Model using MVVM pattern

  - by Dzenand

  I have a database that communicates with webservices with my Model (own thread) and exposes Data Objects. My UI application consists of different Views and ViewModels and Custom Controls. I'm using ServiceProvider (IServiceProvider) to access the Model and route the events to the UI thread. Communication between the ViewModels is handeled by a Messenger. Is this way to go? I was also wondering what is the best way to strucutre the DataObjects At the moment i have the DataObjects that have a hierarchy structure but does not support INotifyProperty though the children list are of type of ObservableCollection. I have no possiblity to implement notifypropertychange on the properties. I was wondering the best way of making them MVVM friendly. Implementing a partial class and adding all the properties or commands that are necessary or wrapping all the DataObjects and keep the Model list and MVVM list in sync. All thoughts and ideas are appreciated.

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• C# MultiThread Safe Class Design

  - by Robert

  I'm trying to designing a class and I'm having issues with accessing some of the nested fields and I have some concerns with how multithread safe the whole design is. I would like to know if anyone has a better idea of how this should be designed or if any changes that should be made? using System; using System.Collections; namespace SystemClass { public class Program { static void Main(string[] args) { System system = new System(); //Seems like an awkward way to access all the members dynamic deviceInstance = (((DeviceType)((DeviceGroup)system.deviceGroups[0]).deviceTypes[0]).deviceInstances[0]); Boolean checkLocked = deviceInstance.locked; //Seems like this method for accessing fields might have problems with multithreading foreach (DeviceGroup dg in system.deviceGroups) { foreach (DeviceType dt in dg.deviceTypes) { foreach (dynamic di in dt.deviceInstances) { checkLocked = di.locked; } } } } } public class System { public ArrayList deviceGroups = new ArrayList(); public System() { //API called to get names of all the DeviceGroups deviceGroups.Add(new DeviceGroup("Motherboard")); } } public class DeviceGroup { public ArrayList deviceTypes = new ArrayList(); public DeviceGroup() {} public DeviceGroup(string deviceGroupName) { //API called to get names of all the Devicetypes deviceTypes.Add(new DeviceType("Keyboard")); deviceTypes.Add(new DeviceType("Mouse")); } } public class DeviceType { public ArrayList deviceInstances = new ArrayList(); public bool deviceConnected; public DeviceType() {} public DeviceType(string DeviceType) { //API called to get hardwareIDs of all the device instances deviceInstances.Add(new Mouse("0001")); deviceInstances.Add(new Keyboard("0003")); deviceInstances.Add(new Keyboard("0004")); //Start thread CheckConnection that updates deviceConnected periodically } public void CheckConnection() { //API call to check connection and returns true this.deviceConnected = true; } } public class Keyboard { public string hardwareAddress; public bool keypress; public bool deviceConnected; public Keyboard() {} public Keyboard(string hardwareAddress) { this.hardwareAddress = hardwareAddress; //Start thread to update deviceConnected periodically } public void CheckKeyPress() { //if API returns true this.keypress = true; } } public class Mouse { public string hardwareAddress; public bool click; public Mouse() {} public Mouse(string hardwareAddress) { this.hardwareAddress = hardwareAddress; } public void CheckClick() { //if API returns true this.click = true; } } }

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• design pattern for related inputs

  - by curiousMo

  My question is a design question : let's say i have a data entry web page with 4 drop down lists, each depending on the previous one, and a bunch of text boxes. ddlCountry (DropDownList) ddlState (DropDownList) ddlCity (DropDownList) ddlBoro (DropDownList) txtAddress (TxtBox) txtZipcode(TxtBox) and an object that represents a datarow with a value for each: countrySeqid stateSeqid citySeqid boroSeqid address zipCode naturally the country, state, city and boro values will be values of primary keys of some lookup tables. when the user chooses to edits that record, i would load it from database and load it into the page. the issue that I have is how to streamline loading the DropDownLists. i have some code that would grab the object,look thru its values and move them to their corresponding input controls in one shot. but in this case i will have to load the ddlCountry with possible values, then assign values, then do the same thing for the rest of the ddls. I guess i am looking for an elegant solution. i am using asp.net, but i think it is irrelevant to the question. i am looking more into a design pattern.

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• Singleton & Multithreading in Java

  - by vivek jagtap

  What is the preferred way to work with Singleton class in multithreaded environment? Suppose if I have 3 thread, and all they try to access getInstance() method of singleton class at the same time - What would happen if no synchronization is maintained? Is it good practice to use synchronized getInstance() method or use synchronized block inside getInstance(). Please advise if there is any other way out.

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• is this a design pattern?

  - by Michel

  Hi all, i have to build some financial data report, and for making the calculation, there are a lot of 'if then' situations: if it's a large client, subtract 10%, if it's postal code equals '10101', add 10%, if the day is on a saturday, make a difficult calculation etc. so i once read about this kind of example, and what they did was (hope i remember well) create a class with some base info and make it possible to add all kinds of calculationobjects to it. So to put what i remembered in pseudo code Basecalc bc = new baseCalc(); //put the info in the bc so other objects can do their if bc.Add(new Largecustomercalc()); bc.Add(new PostalcodeCalc()); bc.add(new WeekdayCalc()); the the bc would run the Calc() methods of all of the added Calc objects. As i type this i think all the Calc objects must be able to see the Basecalc properties to correctly perform their calculation logic. So all the if's are in the different Calc objects and not ALL in the Basecalc. does this make sense? I was wondering if this is some kind of design pattern?

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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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• command design pattern usage

  - by sagie

  Hi. I've read 3 descriptions of the command design pattern: wikipedia, dofactory and source making. In all of them, the UML shows a relation between the client to the receiver & the concrete command, but no relation to the invoker. But in all 3 examples the client is the one that initiates the invoker and call its Execute method. I think that should be a relation to the invoker as well. Am I missing somthing in here? Maybe even a basic UML knowladge?

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• Passing ViewModel for backbone.js from MVC3 Server-Side

  - by Roman

  In ASP.NET MVC there is Model, View and Controller. MODEL represents entities which are stored in database and essentially is all the data used in a application (for example, generated by EntityFramework, "DB First" approach). Not all data from model you want to show in the view (for example, hashs of passwords). So you create VIEW MODEL, each for every strongly-typed-razor-view you have in application. Like this: using System; using System.Collections.Generic; using System.Linq; using System.Web; namespace MyProject.ViewModels.SomeController.SomeAction { public class ViewModel { public ViewModel() { Entities1 = new List<ViewEntity1>(); Entities2 = new List<ViewEntity2>(); } public List<ViewEntity1> Entities1 { get; set; } public List<ViewEntity2> Entities2 { get; set; } } public class ViewEntity1 { //some properties from original DB-entity you want to show } public class ViewEntity2 { } } When you create complex client-side interfaces (I do), you use some pattern for javascript on client, MVC or MVVM (I know only these). So, with MVC on client you have another model (Backbone.Model for example), which is third model in application. It is a bit much. Why don`t we use the same ViewModel model on a client (in backbone.js or another framework)? Is there a way to transfer CS-coded model to JS-coded? Like in MVVM pattern, with knockout.js, when you can do like this: in SomeAction.cshtml: <div style="display: none;" id="view_model">@Json.Encode(Model)</div> after that in Javascript-code var ViewModel = ko.mapping.fromJSON($("#view_model").get(0).innerHTML); now you can extend your ViewModel with some actions, event handlers, etc: ko.utils.extend(ViewModel, { some_function: function () { //some code } }); So, we are not building the same view model on the client again, we are transferring existing view model from server. At least, data. But knockout.js is not suitable for me, you can`t build complex UI with it, it is just data-binding. I need something more structural, like backbone.js. The only way to build ViewModel for backbone.js I can see now is re-writing same ViewModel in JS from server with hands. Is there any ways to transfer it from server? To reuse the same viewmodel on server view and client view?

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• Where do you put your dependencies?

  - by The All Foo

  If I use the dependency injection pattern to remove dependencies they end up some where else. For example, Snippet 1, or what I call Object Maker. I mean you have to instantiate your objects somewhere...so when you move dependency out of one object, you end up putting it another one. I see that this consolidates all my dependencies into one object. Is that the point, to reduce your dependencies so that they all reside in a single ( as close to as possible ) location? Snippet 1 - Object Maker <?php class ObjectMaker { public function makeSignUp() { $DatabaseObject = new Database(); $TextObject = new Text(); $MessageObject = new Message(); $SignUpObject = new ControlSignUp(); $SignUpObject->setObjects($DatabaseObject, $TextObject, $MessageObject); return $SignUpObject; } public function makeSignIn() { $DatabaseObject = new Database(); $TextObject = new Text(); $MessageObject = new Message(); $SignInObject = new ControlSignIn(); $SignInObject->setObjects($DatabaseObject, $TextObject, $MessageObject); return $SignInObject; } public function makeTweet( $DatabaseObject = NULL, $TextObject = NULL, $MessageObject = NULL ) { if( $DatabaseObject == 'small' ) { $DatabaseObject = new Database(); } else if( $DatabaseObject == NULL ) { $DatabaseObject = new Database(); $TextObject = new Text(); $MessageObject = new Message(); } $TweetObject = new ControlTweet(); $TweetObject->setObjects($DatabaseObject, $TextObject, $MessageObject); return $TweetObject; } public function makeBookmark( $DatabaseObject = NULL, $TextObject = NULL, $MessageObject = NULL ) { if( $DatabaseObject == 'small' ) { $DatabaseObject = new Database(); } else if( $DatabaseObject == NULL ) { $DatabaseObject = new Database(); $TextObject = new Text(); $MessageObject = new Message(); } $BookmarkObject = new ControlBookmark(); $BookmarkObject->setObjects($DatabaseObject,$TextObject,$MessageObject); return $BookmarkObject; } }

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• Design pattern: polymorphisim for list of objects

  - by ziang

  Suppose I have a class A, and A1, A2 inherits from A. There are 2 functions: List<A1> getListA1(){...} List<A2> getListA2(){...} Now I want to do something similar to both A1 and A2 in another function public void process(List<A>){...} If I want to pass the instance of either ListA1 or ListA2, of course the types doesn't match because the compiler doesn't allow the coercion from List< A1 to List< A. I can't do something like this: List<A1> listA1 = getListA1(); List<A> newList = (List<A>)listA1; //this is not allowed. So what is the best approach to the process()? Is there any way to do it in a universal way rather than write the similar code to both List and List?

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• Is the provider pattern an implementation of IOC?

  - by blahblah

  Is the provider pattern an implementation of IOC? If not, why not? (reading through martin fowlers article on ioc)

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• What single design or programming decision have you made, that ended up paying off in spades later o

  - by Ross Charette

  What single design or programming decision have you made, that ended up paying off in spades later on?

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• Approaching Java from a Ruby perspective

  - by Travis

  There are plenty of resources available to a Java developer for getting a jump-start into Ruby/Rails development. The reverse doesn't appear to be true. What resources would you suggest for getting up-to-date on the current state of java technologies? How about learning how to approach DRY (don't repeat yourself) without the use of metaprogramming? Or how to approach various scenarios where a ruby developer is used to passing in a function (proc/lambda/block) as an argument (callbacks, etc)?

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• pattern to transfer search model to dao

  - by zeroed

  We have a dao as a project (jar file). Clients use its interfaces and factories to operate with database. Using standard CRUD operations, dao allows you to search an entity by some search criteria. What is the best way to represent this criteria? Is transfer object appropriate pattern in this situation? How should client create SearchModel instance? Please, share. Regards.

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• Function chaining depending on boolean result

  - by Markive

  This is just an efficiency question really.. I'm interested to know if there is a more efficient or logical way that people use to handle this sort of scenario. In my asp.net application I am running a script to generate a new project my code at the top level looks like this: Dim ok As Boolean = True ok = createFolderStructure() If ok Then ok = createMDB() If ok Then ok = createProjectConfig() If ok Then ok = updateCompanyConfig() I create a boolean and each function returns a boolean result, the next function in this chain will only run if the previous one was successful. I do this because an asp.net application will continue to run through the page life cycle unless there is an unhandled exception and I don't want my whole application to be screwed up if something in the chain goes wrong (there is a lot of copying and deleting of files etc.. in this example). I was just wondering how other people handle this scenario? the vb.net single line if statement is quite succinct but I'm wondering if there is a better way?

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• user interface pattern for associating single or many objects to an entity

  - by Samuel

  Need suggestions on implementing associating single or many objects to an entity. All soccer team players are registered individually (e.g. they are part of 'players' table) A soccer team has many players. The click sequence is like this:- a] Soccer team owner provides a name and brief description of the soccer team. b] Now it wants to add players to this team. c] You have the following button 'Add players to team' which lets you navigate to the 'View Players' page and lets you multi select users from there. Assuming this is a paginated list of players, how do you handle the following:- Do you provide a check box against each player and let the manager do a multi selection. If you need to add more players, it doesn't make sense to show the players who have been already added to the team. Do you mark those entries as not selectable or you would adding showing these entries. If you need to filter, do you provide search filters at the top of this page. Am looking for ideas on how to implement this or sites which have already done something similar.

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• What Is Utility Services ?

  - by query_bug

  Hai, I need some information about Utility Services Layer. Can someone Please help me in getting information on that as I am supposed to give a presentation on Utility Services Layer. Thanks in advance...

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• Single-Page Web Apps: Client-side datastores & server persistence

  - by fig-gnuton

  How should client-side datastores & persistence be handled in a single-page web application? Global vars vs. DI/IoC: Should datastores be assigned to global variables so any part of the application can access them? Or should they be dependency injected where required? Server persistence: Assuming a datastore's data needn't always be persisted to the server immediately, should the datastore itself handle persistence? If not, then what class should handle persistence and how should the persistence class fit into the client-side architecture overall? Is the datastore considered the model in MVC, or is it something else since it just stores raw data?

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