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  • Factory Method Implementation

    - by cedar715
    I was going through the 'Factory method' pages in SO and had come across this link. And this comment. The example looked as a variant and thought to implement in its original way: to defer instantiation to subclasses... Here is my attempt. Does the following code implements the Factory pattern of the example specified in the link? Please validate and suggest if this has to undergo any re-factoring. public class ScheduleTypeFactoryImpl implements ScheduleTypeFactory { @Override public IScheduleItem createLinearScheduleItem() { return new LinearScheduleItem(); } @Override public IScheduleItem createVODScheduleItem() { return new VODScheduleItem(); } } public class UseScheduleTypeFactory { public enum ScheduleTypeEnum { CableOnDemandScheduleTypeID, BroadbandScheduleTypeID, LinearCableScheduleTypeID, MobileLinearScheduleTypeID } public static IScheduleItem getScheduleItem(ScheduleTypeEnum scheduleType) { IScheduleItem scheduleItem = null; ScheduleTypeFactory scheduleTypeFactory = new ScheduleTypeFactoryImpl(); switch (scheduleType) { case CableOnDemandScheduleTypeID: scheduleItem = scheduleTypeFactory.createVODScheduleItem(); break; case BroadbandScheduleTypeID: scheduleItem = scheduleTypeFactory.createVODScheduleItem(); break; case LinearCableScheduleTypeID: scheduleItem = scheduleTypeFactory.createLinearScheduleItem(); break; case MobileLinearScheduleTypeID: scheduleItem = scheduleTypeFactory.createLinearScheduleItem(); break; default: break; } return scheduleItem; } }

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  • when to use the abstract factory pattern?

    - by hguser
    Hi: I want to know when we need to use the abstract factory pattern. Here is an example,I want to know if it is necessary. The UML THe above is the abstract factory pattern, it is recommended by my classmate. THe following is myown implemention. I do not think it is necessary to use the pattern. And the following is some core codes: package net; import java.io.IOException; import java.util.HashMap; import java.util.Map; import java.util.Properties; public class Test { public static void main(String[] args) throws IOException, InstantiationException, IllegalAccessException, ClassNotFoundException { DaoRepository dr=new DaoRepository(); AbstractDao dao=dr.findDao("sql"); dao.insert(); } } class DaoRepository { Map<String, AbstractDao> daoMap=new HashMap<String, AbstractDao>(); public DaoRepository () throws IOException, InstantiationException, IllegalAccessException, ClassNotFoundException { Properties p=new Properties(); p.load(DaoRepository.class.getResourceAsStream("Test.properties")); initDaos(p); } public void initDaos(Properties p) throws InstantiationException, IllegalAccessException, ClassNotFoundException { String[] daoarray=p.getProperty("dao").split(","); for(String dao:daoarray) { AbstractDao ad=(AbstractDao)Class.forName(dao).newInstance(); daoMap.put(ad.getID(),ad); } } public AbstractDao findDao(String id) {return daoMap.get(id);} } abstract class AbstractDao { public abstract String getID(); public abstract void insert(); public abstract void update(); } class SqlDao extends AbstractDao { public SqlDao() {} public String getID() {return "sql";} public void insert() {System.out.println("sql insert");} public void update() {System.out.println("sql update");} } class AccessDao extends AbstractDao { public AccessDao() {} public String getID() {return "access";} public void insert() {System.out.println("access insert");} public void update() {System.out.println("access update");} } And the content of the Test.properties is just one line: dao=net.SqlDao,net.SqlDao So any ont can tell me if this suitation is necessary?

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  • Validation with State Pattern for Multi-Page Forms in ASP.NET

    - by philrabin
    I'm trying to implement the state pattern for a multi-page registration form. The data on each page will be accumulated and stored in a session object. Should validation (including service layer calls to the DB) occur on the page level or inside each state class? In other words, should the concrete implementation of IState be concerned with the validation or should it be given a fully populated and valid object? See "EmptyFormState" class below: namespace Example { public class Registrar { private readonly IState formEmptyState; private readonly IState baseInformationComplete; public RegistrarSessionData RegistrarSessionData { get; set;} public Registrar() { RegistrarSessionData = new RegistrarSessionData(); formEmptyState = new EmptyFormState(this); baseInformationComplete = new BasicInfoCompleteState(this); State = formEmptyState; } public IState State { get; set; } public void SubmitData(RegistrarSessionData data) { State.SubmitData(data); } public void ProceedToNextStep() { State.ProceedToNextStep(); } } //actual data stored in the session //to be populated by page public class RegistrarSessionData { public string FirstName { get; set; } public string LastName { get; set; } //will include values of all 4 forms } //State Interface public interface IState { void SubmitData(RegistrarSessionData data); void ProceedToNextStep(); } //Concrete implementation of IState //Beginning state - no data public class EmptyFormState : IState { private readonly Registrar registrar; public EmptyFormState(Registrar registrar) { this.registrar = registrar; } public void SubmitData(RegistrarSessionData data) { //Should Validation occur here? //Should each state object contain a validation class? (IValidator ?) //Should this throw an exception? } public void ProceedToNextStep() { registrar.State = new BasicInfoCompleteState(registrar); } } //Next step, will have 4 in total public class BasicInfoCompleteState : IState { private readonly Registrar registrar; public BasicInfoCompleteState(Registrar registrar) { this.registrar = registrar; } public void SubmitData(RegistrarSessionData data) { //etc } public void ProceedToNextStep() { //etc } } }

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  • Database Replication OOD Pattern

    - by MrOnigiri
    Greetings fellow overflowers, After reading on MSDN about correct strategies on how to perform database replication, and understanding their suggestion on Master-Subordinate Incremental Replication. It left me wondering, what OOD design pattern should I use on this... The main elements of this strategy are the Acquirer, the Manipulator and the Writer. The first fetches data from the database and passes on to the second which might perform simple transformations to the data, before handling it to the final element, the writer, that writes the desired data on the destination Database. I thought about using the Chain of Responsibility pattern, but the Acquirer, Manipulator and Writer don't share a common role among theme, so It makes no sense. Should these elements be written as separate classes, or methods inside my service? Of course I'll be creating a DB Helper class as well, but that doesn't constitutes a problem. Wondering what your opinions on this are! Thanks for your replies

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  • Best practice for DAO pattern ?

    - by Tony
    I've seen a lot of codes use a service-dao pattern , I don't know the origin of this pattern . It force the front layer call service , then delegates some of the service task to dao. I want to ask : Does DAO layer do purely data access related task ? What about exception encapsulation ? Is there other pattern can be used to replace this ?

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  • Is ASP.NET MVC is really MVC? Or how to separate model from controller?

    - by Andrey
    Hi all, This question is a bit rhetorical. At some point i got a feeling that ASP.NET MVC is not that authentic implementation of MVC pattern. Or i didn't understood it. Consider following domain: electric bulb, switch and motion detector. They are connected together and when you enter the room motion detector switches on the bulb. If i want to represent them as MVC: switch is model, because it holds the state and contains logic bulb is view, because it presents the state of model to human motion detector is controller, because it converts user actions to generic model commands Switch has one private field (On/Off) as a State and two methods (PressOn, PressOff). If you call PressOn when it is Off it goes to On, if you call it again state doesn't change. Bulb can be replaced with buzzer, motion detector with timer or button, but the model still represent the same logic. Eventually system will have same behavior. This is how i understand classical MVC decomposition, please correct me if i am wrong. Now let's decompose it in ASP.Net MVC way. Bulb is still a view Controller will be switch + motion detector Model is some object that will just pass state to bulb. So the logic that defines behavior moves to controller. Question 1: Is my understanding of MVC and ASP.NET MVC correct? Question 2: If yes, do you agree that ASP.NET MVC is not 100% accurate implementation? And back to life. The final question is how to separate model from controller in case of ASP.NET MVC. There can be two extremes. Controller does basic stuff and call model to do all the logic. Another is controller does all the logic and model is just something like class with properties that is mapped to DB. Question 3: Where should i draw the line between this extremes? How to balance? Thanks, Andrey

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  • Design Question on when to save

    - by Ben
    Hi, I was just after peoples opinion on when the best time to save an object (or collection of objects) is. I appreciate that it can be completely dependent on the situation that you are in but here is my situation. I have a collection of objects "MyCollection" in a grid. You can open each object "MyObject" in an editor dialogue by double clicking on the grid. Selecting "Cancel" on the dialogue will back out any changes you have made, but should selecting "ok" commit those changes back to the database, or should they commit the changes on that object back to the collection and have a save method that iterates through the collection and saves all changed objects? If i have an object "MyParentObject", that contains a collection of childen "MyChildObjectCollection", none of the changes made to each "MyChildObject" would be commited to the database until the "MyParentObject" was saved - this makes sense. However in my current situation, none of the objects in the collection are linked, therefore should the "Ok" on the dialogue commit the changes to the database? Appreciate any opinions on this. Thanks

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  • How to design this class hierarchy?

    - by devoured elysium
    I have defined an Event class: Event and all the following classes inherit from Event: AEvent BEvent CEvent DEvent Now, with the info I gather from all these Event classes, I will make a chart. With AEvent and BEvent, I will generate points for that chart, while with CEvent and DEvent I will paint certain regions of the chart. Now, how should I signal this in my class hierarchy? Should I make AEvent and BEvent inherit from PointEvent while CEvent and DEvent inherit from RegionEvent, being that both RegionEvent and PointEvent inherit from Event? Should I add a field with an Enum to Event with 2 values, Point and Region, and each of the child classes set their value to it? Should I use some kind of pattern here? Which one? Thanks.

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  • Which Code Should Go Where in MVC Structure

    - by Oguz
    My problem is in somewhere between model and controller.Everything works perfect for me when I use MVC just for crud (create, read, update, delete).I have separate models for each database table .I access these models from controller , to crud them . For example , in contacts application,I have actions (create, read, update, delete) in controller(contact) to use model's (contact) methods (create, read, update, delete). The problem starts when I try to do something more complicated. There are some complex processes which I do not know where should I put them. For example , in registering user process. I can not just finish this process in user model because , I have to use other models too (sending mails , creating other records for user via other models) and do lots of complex validations via other models. For example , in some complex searching processes , I have to access lots of models (articles, videos, images etc.) Or, sometimes , I have to use apis to decide what I will do next or which database model I will use to record data So where is the place to do this complicated processes. I do not want to do them in controllers , Because sometimes I should use these processes in other controllers too. And I do not want to put these process in models because , I use models as database access layers .May be I am wrong,I want to know . Thank you for your answer .

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  • Design pattern question: encapsulation or inheritance

    - by Matt
    Hey all, I have a question I have been toiling over for quite a while. I am building a templating engine with two main classes Template.php and Tag.php, with a bunch of extension classes like Img.php and String.php. The program works like this: A Template object creates a Tag objects. Each tag object determines which extension class (img, string, etc.) to implement. The point of the Tag class is to provide helper functions for each extension class such as wrap('div'), addClass('slideshow'), etc. Each Img or String class is used to render code specific to what is required, so $Img->render() would give something like <img src='blah.jpg' /> My Question is: Should I encapsulate all extension functionality within the Tag object like so: Tag.php function __construct($namespace, $args) { // Sort out namespace to determine which extension to call $this->extension = new $namespace($this); // Pass in Tag object so it can be used within extension return $this; // Tag object } function render() { return $this->extension->render(); } Img.php function __construct(Tag $T) { $args = $T->getArgs(); $T->addClass('img'); } function render() { return '<img src="blah.jpg" />'; } Usage: $T = new Tag("img", array(...); $T->render(); .... or should I create more of an inheritance structure because "Img is a Tag" Tag.php public static create($namespace, $args) { // Sort out namespace to determine which extension to call return new $namespace($args); } Img.php class Img extends Tag { function __construct($args) { // Determine namespace then call create tag $T = parent::__construct($namespace, $args); } function render() { return '<img src="blah.jpg" />'; } } Usage: $Img = Tag::create('img', array(...)); $Img->render(); One thing I do need is a common interface for creating custom tags, ie I can instantiate Img(...) then instantiate String(...), I do need to instantiate each extension using Tag. I know this is somewhat vague of a question, I'm hoping some of you have dealt with this in the past and can foresee certain issues with choosing each design pattern. If you have any other suggestions I would love to hear them. Thanks! Matt Mueller

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  • c# Attribute Question

    - by Petoj
    Well i need some help here i don't know how to solve this problem. the function of the attribute is to determine if the function can be run... So what i need is the following: The consumer of the attribute should be able to determine if it can be executed. The owner of the attribute should be able to tell the consumer that now it can/can't be executed (like a event). It must have a simple syntax. This is what i have so far but it only implements point 1, 3. [AttributeUsage(AttributeTargets.Method, AllowMultiple = false)] public class ExecuteMethodAttribute : Attribute { private Func<object, bool> canExecute; public Func<object, bool> CanExecute { get { return canExecute; } } public ExecuteMethodAttribute() { } public ExecuteMethodAttribute(Func<object, bool> canExecute) { this.canExecute = canExecute; } }

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  • Design suggestions for creating document management structure using hidden shares.

    - by focus.nz
    I need to add some document management functionality into my software. Documents will be grouped by company name and project name. The folders need to be accessed by the application using the id numbers of clients/projects, but also easily browsed by the end user using windows explorer. Clients and Projects will be stored in a database. I am thinking of having the software create the folders using the friendly name and then using a hidden share with the id number for the software to access the files. The folder structure would be something like this --Company 1 (Company-1234$) -- Project 101 (Project-101$) -- Project 102 (Project-102$) -- Project 103 (Project-103$) -- Company 2 (Company-5678$) -- Project 201 (Project-201$) -- Project 202 (Project-202$) -- Project 203 (Project-203$) So in the example above there would be a company called "Company 1" with a ID of "1234". When browsing the folders using windows explorer the user would see \\ServerName\Documents\Company1 and you could also access the same folder from \\ServerName\Documents\Company-1234$ By using the hidden share, if the company name changes or its renamed for some reason it doesn't break the link in the application because its using the hidden shared based on the ID that never changes. Will having hundreds (maybe thousands) or hidden shares on a server provide a huge performance hit? Does any one have any suggestions or alternatives to provide this feature?

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  • Tracking the user function that threw the exception

    - by makerofthings7
    I've been given a large application with only one try..catch at the outer most level. This application also throws exceptions all the time, and is poorly documented. Is there any pattern I can implement that will tell me what user method is being called, the exception being thrown, and also the count of exceptions? I'm thinking of using a dictionary with reflection to get the needed information, but I'm not sure if this will work. What do you think?

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  • IoC, Containers, and NServiceBus confusion

    - by andy
    Hey guys, here's my setup Castle Windsor is my container NServiceBus is itself using it's own container internally, Spring by default I'm implementing the PubSub config. Ok, if I have my Bus.Publish happening within my IWantToRunAtStartup class, then everything is fine. As a test for example on Run() we can start a timer and it'll go into a Service style loop. However, what if I want to abstract NServiceBus from my app, and have my app go: new CustomPulisherClass().Notify(ISomeMessage msg); In this situation, how do I implement CustomPublisherClass. My confusion is coming from the fact that NServiceBus is already running as a Service, it's already been "Started". How to I get at the correct instance of the Bus object? cheers andy

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  • Design question what pattern to use

    - by rahul
    Problem Description: We have a requirement of storing the snapshot of an entity temporarily in the database untill a certain period of time untill all the processes to approve the data are completed. Once all approvals are completed the data shall be permanantly persisted into the actual table. Example: 1) Consider an entity called "User". One way to create the user is through the "Create Account Process". 2) The "Create Account Process" shall capture all the information of the User and store it in a temporary table in the database. 3) The data shall be used by the "Account Approval Process" to run its verification process. 4. After all the verification is completed successfully, the User data shall be persisted to the actual table. Question: Where to store the user data entered during "Create Account Process". Additionally, User data should be editable till the verification process is complete.

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  • UML Class Relationships

    - by 01010011
    Hi, I would like to confirm whether I am on the right track when identifying common UML class relationships. For example, is the relationship between: 1 a stackoverflow member and his/her stackoverflow user account categorized as a composition relationship or an aggregation relationship? At first I thought it was an association because this member "has a" account. However on second thought, I am thinking its composition because each "part" (user account) belongs to only one whole (user) at a time, meaning for as long as I am logged into stackoverflow, I have to use this one and only account until I log off. If I log back onto stackoverflow with a different account then its composition again. Do you agree? 2 a database and a person's user account an aggregation relationship? I think so because 1 database (the whole) can store 0...* number of user accounts (the parts) but another database can store the same user accounts. Finally, can anyone recommend a website that specializes in designing code using UML? Thanks in advance

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  • What's the best practice way to convert enum to string?

    - by dario
    Hi. I have enum like this: public enum ObectTypes { TypeOne, TypeTwo, TypeThree, ... TypeTwenty } then I need to convert this enum to string. Now Im doing this that way: public string ConvertToCustomTypeName(ObjectTypes typeObj) { string result = string.Empty; switch (typeObj) { case ObjectTypes.TypeOne: result = "This is type T123"; break; case ObjectTypes.TypeTwo: result = "This is type T234"; break; ... case ObjectTypes.TypeTwenty: result = "This is type last"; break; } return result; } Im quite sure that there is better way do do this, Im looking for some good practice solution. Thanks in advance.

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  • How to avoid injecting dependencies into an object so that it can pass them on?

    - by Pheter
    I am interested in applying dependency injection to my current project, which makes use of the MVC pattern. My controllers will call the models and therefore will need to inject the dependencies into the models. To do this, the controller must have the dependencies (such as a database object) in the first place. The controller doesn't need to make use of some of these dependencies (such as the database object), so I feel that it shouldn't be given this dependency. However, it has to have these dependencies if it is to inject them into the model objects. How can I avoid having dependencies injected into an object just so that it can pass them on? Doing so feels wrong and can result in many dependencies being injected into an object. Edit: I am using PHP.

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  • How to restrict access to a class's data based on state?

    - by Marcus Swope
    In an ETL application I am working on, we have three basic processes: Validate and parse an XML file of customer information from a third party Match values received in the file to values in our system Load customer data in our system The issue here is that we may need to display the customer information from any or all of the above states to an internal user and there is data in our customer class that will never be populated before the values have been matched in our system (step 2). For this reason, I would like to have the values not even be available to be accessed when the customer is in this state, and I would like to have to avoid some repeated logic everywhere like: if (customer.IsMatched) DisplayTextOnWeb(customer.SomeMatchedValue); My first thought for this was to add a couple interfaces on top of Customer that would only expose the properties and behaviors of the current state, and then only deal with those interfaces. The problem with this approach is that there seems to be no good way to move from an ICustomerWithNoMatchedValues to an ICustomerWithMatchedValues without doing direct casts, etc... (or at least I can't find one). I can't be the first to have come across this, how do you normally approach this? As a last caveat, I would like for this solution to play nice with FluentNHibernate :) Thanks in advance...

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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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  • Design pattern for cost calculator app?

    - by Anders Svensson
    Hi, I have a problem that I’ve tried to get help for before, but I wasn’t able to solve it then, so I’m trying to simplify the problem now to see if I can get some more concrete help with this because it is driving me crazy… Basically, I have a working (more complex) version of this application, which is a project cost calculator. But because I am at the same time trying to learn to design my applications better, I would like some input on how I could improve this design. Basically the main thing I want is input on the conditionals that (here) appear repeated in two places. The suggestions I got before was to use the strategy pattern or factory pattern. I also know about the Martin Fowler book with the suggestion to Refactor conditional with polymorphism. I understand that principle in his simpler example. But how can I do either of these things here (if any would be suitable)? The way I see it, the calculation is dependent on a couple of conditions: 1. What kind of service is it, writing or analysis? 2. Is the project small, medium or large? (Please note that there may be other parameters as well, equally different, such as “are the products new or previously existing?” So such parameters should be possible to add, but I tried to keep the example simple with only two parameters to be able to get concrete help) So refactoring with polymorphism would imply creating a number of subclasses, which I already have for the first condition (type of service), and should I really create more subclasses for the second condition as well (size)? What would that become, AnalysisSmall, AnalysisMedium, AnalysisLarge, WritingSmall, etc…??? No, I know that’s not good, I just don’t see how to work with that pattern anyway else? I see the same problem basically for the suggestions of using the strategy pattern (and the factory pattern as I see it would just be a helper to achieve the polymorphism above). So please, if anyone has concrete suggestions as to how to design these classes the best way I would be really grateful! Please also consider whether I have chosen the objects correctly too, or if they need to be redesigned. (Responses like "you should consider the factory pattern" will obviously not be helpful... I've already been down that road and I'm stumped at precisely how in this case) Regards, Anders The code (very simplified, don’t mind the fact that I’m using strings instead of enums, not using a config file for data etc, that will be done as necessary in the real application once I get the hang of these design problems): public abstract class Service { protected Dictionary<string, int> _hours; protected const int SMALL = 2; protected const int MEDIUM = 8; public int NumberOfProducts { get; set; } public abstract int GetHours(); } public class Writing : Service { public Writing(int numberOfProducts) { NumberOfProducts = numberOfProducts; _hours = new Dictionary<string, int> { { "small", 125 }, { "medium", 100 }, { "large", 60 } }; } public override int GetHours() { if (NumberOfProducts <= SMALL) return _hours["small"] * NumberOfProducts; if (NumberOfProducts <= MEDIUM) return (_hours["small"] * SMALL) + (_hours["medium"] * (NumberOfProducts - SMALL)); return (_hours["small"] * SMALL) + (_hours["medium"] * (MEDIUM - SMALL)) + (_hours["large"] * (NumberOfProducts - MEDIUM)); } } public class Analysis : Service { public Analysis(int numberOfProducts) { NumberOfProducts = numberOfProducts; _hours = new Dictionary<string, int> { { "small", 56 }, { "medium", 104 }, { "large", 200 } }; } public override int GetHours() { if (NumberOfProducts <= SMALL) return _hours["small"]; if (NumberOfProducts <= MEDIUM) return _hours["medium"]; return _hours["large"]; } } public partial class Form1 : Form { public Form1() { InitializeComponent(); List<int> quantities = new List<int>(); for (int i = 0; i < 100; i++) { quantities.Add(i); } comboBoxNumberOfProducts.DataSource = quantities; } private void comboBoxNumberOfProducts_SelectedIndexChanged(object sender, EventArgs e) { Service writing = new Writing((int) comboBoxNumberOfProducts.SelectedItem); Service analysis = new Analysis((int) comboBoxNumberOfProducts.SelectedItem); labelWriterHours.Text = writing.GetHours().ToString(); labelAnalysisHours.Text = analysis.GetHours().ToString(); } }

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