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  • Let a model instance choose appropriate view class using category. Is it good design?

    - by Denis Mikhaylov
    Assume I have abstract base model class called MoneySource. And two realizations BankCard and CellularAccount. In MoneysSourceListViewController I want to display a list of them, but with ListItemView different for each MoneySource subclass. What if I define a category on MoneySource @interface MoneySource (ListItemView) - (Class)listItemViewClass; @end And then override it for each concrete sublcass of MoneySource, returning suitable view class. @implementation CellularAccount (ListItemView) - (Class)listItemViewClass { return [BankCardListView class]; } @end @implementation BankCard (ListItemView) - (Class)listItemViewClass { return [CellularAccountListView class]; } @end so I can ask model object about its view, not violating MVC principles, and avoiding class introspection or if constructions. Thank you!

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  • Is there a 'design pattern' type listing of common algorithms?

    - by KevinM1
    Is there a 'design pattern' styled listing of common/popular algorithms anywhere? Specifically, something that has a similar format along the lines of: Algorithm Name: e.g., Quick Sort, Bubble Sort, etc. Problem: A description of the stereotypical problem the algorithm is supposed to address Description: Description of the solution Implementation: Code examples of the solution Big O Rating: Self-explanatory Similar Algorithms: Algorithms that address the same problem in different ways, or similar problems I really like the GoF design pattern listing style, and I think it would help me learn various algorithms better/easier if I could find a resource that was similar in terms of organization.

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  • Choices in Architecture, Design, Algorithms, Data Structures for effective RDF Reasoning and Querying in a Big Data Environment [on hold]

    - by user2891213
    As part of my academic project I would like to know what choices in Architecture, Design, Algorithms, Data Structures do we need in order to provide effective and efficient RDF Reasoning and Querying in a Big Data Environment. Basically I want to get info regarding below points: What are the Systems and Software to get appropriate Architecture? What kind of API layer(s) would we need on top of the Big Data stores, to make this possible? The Indexing structures we will need. The appropriate Algorithms, and appropriate Algorithms for Query Planning across Big Data stores. The Performance Analysis and Cost Models we will need to justify the design decisions we have made along the way. Can anyone please provide pointers.. Thanks, David

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  • Evolving Architectures &ndash; Part II but Design is emergent

    This is part II of a series on agile architecture. You can read part I here. In the previous installment I provided a definition for software architecture and raised the apparent friction between the up front design implied by software architecture and the YAGNI approach and deferred requirements prompted by agile development in the large. This installment take a look at an additional angle of the problem which is the difference between design and architecture (while...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Adding functionality to any TextReader

    - by strager
    I have a Location class which represents a location somewhere in a stream. (The class isn't coupled to any specific stream.) The location information will be used to match tokens to location in the input in my parser, to allow for nicer error reporting to the user. I want to add location tracking to a TextReader instance. This way, while reading tokens, I can grab the location (which is updated by the TextReader as data is read) and give it to the token during the tokenization process. I am looking for a good approach on accomplishing this goal. I have come up with several designs. Manual location tracking Every time I need to read from the TextReader, I call AdvanceString on the Location object of the tokenizer with the data read. Advantages Very simple. No class bloat. No need to rewrite the TextReader methods. Disadvantages Couples location tracking logic to tokenization process. Easy to forget to track something (though unit testing helps with this). Bloats existing code. Plain TextReader wrapper Create a LocatedTextReaderWrapper class which surrounds each method call, tracking a Location property. Example: public class LocatedTextReaderWrapper : TextReader { private TextReader source; public Location Location { get; set; } public LocatedTextReaderWrapper(TextReader source) : this(source, new Location()) { } public LocatedTextReaderWrapper(TextReader source, Location location) { this.Location = location; this.source = source; } public override int Read(char[] buffer, int index, int count) { int ret = this.source.Read(buffer, index, count); if(ret >= 0) { this.location.AdvanceString(string.Concat(buffer.Skip(index).Take(count))); } return ret; } // etc. } Advantages Tokenization doesn't know about Location tracking. Disadvantages User needs to create and dispose a LocatedTextReaderWrapper instance, in addition to their TextReader instance. Doesn't allow different types of tracking or different location trackers to be added without layers of wrappers. Event-based TextReader wrapper Like LocatedTextReaderWrapper, but decouples it from the Location object raising an event whenever data is read. Advantages Can be reused for other types of tracking. Tokenization doesn't know about Location tracking or other tracking. Can have multiple, independent Location objects (or other methods of tracking) tracking at once. Disadvantages Requires boilerplate code to enable location tracking. User needs to create and dispose the wrapper instance, in addition to their TextReader instance. Aspect-orientated approach Use AOP to perform like the event-based wrapper approach. Advantages Can be reused for other types of tracking. Tokenization doesn't know about Location tracking or other tracking. No need to rewrite the TextReader methods. Disadvantages Requires external dependencies, which I want to avoid. I am looking for the best approach in my situation. I would like to: Not bloat the tokenizer methods with location tracking. Not require heavy initialization in user code. Not have any/much boilerplate/duplicated code. (Perhaps) not couple the TextReader with the Location class. Any insight into this problem and possible solutions or adjustments are welcome. Thanks! (For those who want a specific question: What is the best way to wrap the functionality of a TextReader?) I have implemented the "Plain TextReader wrapper" and "Event-based TextReader wrapper" approaches and am displeased with both, for reasons mentioned in their disadvantages.

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  • Core Data Migration - "Can't add source store" error

    - by Tofrizer
    Hi, In my iPhone app I'm using Core Data and I've made changes to my data model that cannot be automatically migrated over (i.e. added new relationships). I added the data model version (Design - Data Model - Add Model Version) and applied my new data model changes to the new version 2. I then created a mapping object model and set the Source and Destination models to their correct data models (old and new respectively). When I run the app and call the persistentStoreCoordinator, my app barfs with the following: 2010-02-27 02:40:30.922 XXXX[73578:20b] Unresolved error Error Domain=NSCocoaErrorDomain Code=134110 UserInfo=0xfc2240 "Operation could not be completed. (Cocoa error 134110.)", { NSUnderlyingError = Error Domain=NSCocoaErrorDomain Code=134130 UserInfo=0xfbb3a0 "Operation could not be completed. (Cocoa error 134130.)"; reason = "Can't add source store"; } FWIW (not much i think) I've also made the usual code changes in persistentStoreCoordinator to use the NSMigratePersistentStoresAutomaticallyOption and NSInferMappingModelAutomaticallyOption (for future data model changes that can be automatically migrated). More relevantly, my managedObjectModel is created by calling initWithContentsOfURL where the file/resource type is "momd". I've tried updating both the source and destination model in the mapping model (Design - Mapping Model - Update XXX Model) as well as deleted the mapping model and recreated it. I've cleaned and re-built but all to no avail. I still get the above error message. Any pointers/thoughts on how I can further debug or resolve this problem please? I haven't posted any code snippets because this feels much more like a build environment issue (and my code is very standard - just the usual core data code to handle migrations using a mapping model but I'm happy to show the code if it helps). Appreciate any help. Thanks

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  • Box2dx: Usage of World.QueryAABB?

    - by Rosarch
    I'm using Box2dx with C#/XNA. I'm trying to write a function that determines if a body could exist in a given point without colliding with anything: /// <summary> /// Can gameObject exist with start Point without colliding with anything? /// </summary> internal bool IsAvailableArea(GameObjectModel model, Vector2 point) { Vector2 originalPosition = model.Body.Position; model.Body.Position = point; // less risky would be to use a deep clone AABB collisionBox; model.Body.GetFixtureList().GetAABB(out collisionBox); // how is this supposed to work? physicsWorld.QueryAABB(x => true, ref collisionBox); model.Body.Position = originalPosition; return true; } Is there a better way to go about doing this? How is World.QueryAABB supposed to work? Here is an earlier attempt. It is broken; it always returns false. /// <summary> /// Can gameObject exist with start Point without colliding with anything? /// </summary> internal bool IsAvailableArea(GameObjectModel model, Vector2 point) { Vector2 originalPosition = model.Body.Position; model.Body.Position = point; // less risky would be to use a deep clone AABB collisionBox; model.Body.GetFixtureList().GetAABB(out collisionBox); ICollection<GameObjectController> gameObjects = worldQueryEngine.GameObjectsForPredicate(x => ! x.Model.Passable); foreach (GameObjectController controller in gameObjects) { AABB potentialCollidingBox; controller.Model.Body.GetFixtureList().GetAABB(out potentialCollidingBox); if (AABB.TestOverlap(ref collisionBox, ref potentialCollidingBox)) { model.Body.Position = originalPosition; return false; // there is something that will collide at this point } } model.Body.Position = originalPosition; return true; }

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  • Getting error while opening form in visual studio 2005

    - by Ravisha
    i am getting below excetion on opening a form on visual studio work bench Its not always but sometime it opens without any problem Does anyone has a solution for this? The path is not of a legal form. Hide at System.IO.Path.NormalizePathFast(String path, Boolean fullCheck) at System.IO.Path.NormalizePath(String path, Boolean fullCheck) at System.IO.Path.GetFullPathInternal(String path) at System.Reflection.AssemblyName.GetAssemblyName(String assemblyFile) at Microsoft.VisualStudio.Design.VSTypeResolutionService.AddProjectDependencies(Project project) at Microsoft.VisualStudio.Design.VSTypeResolutionService.AssemblyEntry.get_Assembly() at Microsoft.VisualStudio.Design.VSTypeResolutionService.AssemblyEntry.Search(String fullName, String typeName, Boolean ignoreTypeCase, Assembly& assembly, String description) at Microsoft.VisualStudio.Design.VSTypeResolutionService.SearchProjectEntries(AssemblyName assemblyName, String typeName, Boolean ignoreTypeCase, Assembly& assembly) at Microsoft.VisualStudio.Design.VSTypeResolutionService.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase, ReferenceType refType) at Microsoft.VisualStudio.Design.Serialization.CodeDom.AggregateTypeResolutionService.GetType(String name, Boolean throwOnError, Boolean ignoreCase) at Microsoft.VisualStudio.Design.Serialization.CodeDom.AggregateTypeResolutionService.GetType(String name, Boolean throwOnError) at System.ComponentModel.Design.Serialization.CodeDomSerializerBase.GetType(ITypeResolutionService trs, String name, Dictionary2 names) at System.ComponentModel.Design.Serialization.CodeDomSerializerBase.FillStatementTable(IDesignerSerializationManager manager, IDictionary table, Dictionary2 names, CodeStatementCollection statements, String className) at System.ComponentModel.Design.Serialization.TypeCodeDomSerializer.Deserialize(IDesignerSerializationManager manager, CodeTypeDeclaration declaration) at System.ComponentModel.Design.Serialization.CodeDomDesignerLoader.PerformLoad(IDesignerSerializationManager manager) at Microsoft.VisualStudio.Design.Serialization.CodeDom.VSCodeDomDesignerLoader.PerformLoad(IDesignerSerializationManager serializationManager) at Microsoft.VisualStudio.Design.Serialization.CodeDom.VSCodeDomDesignerLoader.DeferredLoadHandler.Microsoft.VisualStudio.TextManager.Interop.IVsTextBufferDataEvents.OnLoadCompleted(Int32 fReload)

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  • Best Practise/Subjective: Implement a finite state automaton in OOP

    - by poeschlorn
    Hi guys, I am thinking about implementing a programm with finite state automaton in an OOP language like Java or C++. What would you think is the best way to implement this with a manageable amount of available states, regarding to good software design? Is it good to implement for each state an own class? If yes, how to do the bridge between two states? Thanks for any comment!

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  • GUID type in database

    - by 5YrsLaterDBA
    GUID is not an official data type in database. In our existing SQL Server design, the Uniqueidentifier type is used for GUID value. Now we are switching to Sybase database. Should we use varchar(36) to replace that Uniqueidentifier type? I am still confused by GUID. I was told GUID is 16 bytes long but its character string is 36 characters in length. I must missed something.

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  • Dynamic Programming Algorithm?

    - by scardin
    I am confused about how best to design this algorithm. A ship has x pirates, where the age of the jth pirate is aj and the weight of the jth pirate is wj. I am thinking of a dynamic programming algorithm, which will find the oldest pirate whose weight is in between twenty-fifth and seventy-fifth percentile of all pirates. But I am clueless as to how to proceed.

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  • Accessibility and usability issues when designing websites for older computer users

    - by Vafello
    As a part of my final year university project I am designing a social networking website targeted mainly to older users. I was wondering what accessibility and usability issues should be taken into account when creating a website for such users, apart from obvious ones - such as bigger font, compatibility with current standards, straight-forward interface. Or maybe an older user is just the same as an average user and no special design is needed? Let me know what you think. Thanks.

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  • Java Singleton Pattern

    - by Spencer
    I'm used the Singleton Design Pattern public class Singleton { private static final Singleton INSTANCE = new Singleton(); // Private constructor prevents instantiation from other classes private Singleton() {} public static Singleton getInstance() { return INSTANCE; } } My question is how do I create an object of class Singleton in another class? I've tried: Singleton singleton = new Singleton(); // error - constructor is private Singleton singleton = Singleton.getInstance(); // error - non-static method cannot be referenced from a static context What is the correct code? Thanks, Spencer

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  • Explicit behavior with checks vs. implicit behavior

    - by Silviu
    I'm not sure how to construct the question but I'm interested to know what do you guys think of the following situations and which one would you prefer. We're working at a client-server application with winforms. And we have a control that has some fields automatically calculated upon filling another field. So we're having a field currency which when filled by the user would determine an automatic filling of another field, maybe more fields. When the user fills the currency field, a Currency object would be retrieved from a cache based on the string introduced by the user. If entered currency is not found in the cache a null reference is returned by the cache object. Further down when asking the application layer to compute the other fields based on the currency, given a null currency a null specific field would be returned. This way the default, implicit behavior is to clear all fields. Which is the expected behavior. What i would call the explicit implementation would be to verify that the Currency object is null in which case the depending fields are cleared explicitly. I think that the latter version is more clear, less error prone and more testable. But it implies a form of redundancy. The former version is not as clear and it implies a certain behavior from the application layer which is not expressed in the tests. Maybe in the lower layer tests but when the need arises to modify the lower layers, so that given a null currency something else should be returned, i don't think a test that says just that without a motivation is going to be an impediment for introducing a bug in upper layers. What do you guys think?

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  • database----database normalization

    - by runeveryday
    someone told me the following table isn't fit for the second database normalization. but i don't know why? i am a newbie of database design, i have read some tutorials of the 3NF. but to the 2NF and 3NF, i can't understand them well. expect someone can explain it for me. thank you, +------------+-----------+-------------------+ pk pk row +------------+-----------+-------------------+ A B C +------------+-----------+-------------------+ A D C +------------+-----------+-------------------+ A E C +------------+-----------+-------------------+

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  • Star Schema vs Snowflake Schema performance

    - by Megawolt
    Hi... I'm begin to developing a scial sharing website so I'm curious about database design Schema... So in Data-Mining Star-Schema is the best one but how about a social sharing website... And as a nature of the SS websites there will be (i hope :)) many users in same time... Which better for performance for overdose using...

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  • Big smart ViewModels, dumb Views, and any model, the best MVVM approach?

    - by Edward Tanguay
    The following code is a refactoring of my previous MVVM approach (Fat Models, skinny ViewModels and dumb Views, the best MVVM approach?) in which I moved the logic and INotifyPropertyChanged implementation from the model back up into the ViewModel. This makes more sense, since as was pointed out, you often you have to use models that you either can't change or don't want to change and so your MVVM approach should be able to work with any model class as it happens to exist. This example still allows you to view the live data from your model in design mode in Visual Studio and Expression Blend which I think is significant since you could have a mock data store that the designer connects to which has e.g. the smallest and largest strings that the UI can possibly encounter so that he can adjust the design based on those extremes. Questions: I'm a bit surprised that I even have to "put a timer" in my ViewModel since it seems like that is a function of INotifyPropertyChanged, it seems redundant, but it was the only way I could get the XAML UI to constantly (once per second) reflect the state of my model. So it would be interesting to hear anyone who may have taken this approach if you encountered any disadvantages down the road, e.g. with threading or performance. The following code will work if you just copy the XAML and code behind into a new WPF project. XAML: <Window x:Class="TestMvvm73892.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:local="clr-namespace:TestMvvm73892" Title="Window1" Height="300" Width="300"> <Window.Resources> <ObjectDataProvider x:Key="DataSourceCustomer" ObjectType="{x:Type local:CustomerViewModel}" MethodName="GetCustomerViewModel"/> </Window.Resources> <DockPanel DataContext="{StaticResource DataSourceCustomer}"> <StackPanel DockPanel.Dock="Top" Orientation="Horizontal"> <TextBlock Text="{Binding Path=FirstName}"/> <TextBlock Text=" "/> <TextBlock Text="{Binding Path=LastName}"/> </StackPanel> <StackPanel DockPanel.Dock="Top" Orientation="Horizontal"> <TextBlock Text="{Binding Path=TimeOfMostRecentActivity}"/> </StackPanel> </DockPanel> </Window> Code Behind: using System; using System.Windows; using System.ComponentModel; using System.Threading; namespace TestMvvm73892 { public partial class Window1 : Window { public Window1() { InitializeComponent(); } } //view model public class CustomerViewModel : INotifyPropertyChanged { private string _firstName; private string _lastName; private DateTime _timeOfMostRecentActivity; private Timer _timer; public string FirstName { get { return _firstName; } set { _firstName = value; this.RaisePropertyChanged("FirstName"); } } public string LastName { get { return _lastName; } set { _lastName = value; this.RaisePropertyChanged("LastName"); } } public DateTime TimeOfMostRecentActivity { get { return _timeOfMostRecentActivity; } set { _timeOfMostRecentActivity = value; this.RaisePropertyChanged("TimeOfMostRecentActivity"); } } public CustomerViewModel() { _timer = new Timer(CheckForChangesInModel, null, 0, 1000); } private void CheckForChangesInModel(object state) { Customer currentCustomer = CustomerViewModel.GetCurrentCustomer(); MapFieldsFromModeltoViewModel(currentCustomer, this); } public static CustomerViewModel GetCustomerViewModel() { CustomerViewModel customerViewModel = new CustomerViewModel(); Customer currentCustomer = CustomerViewModel.GetCurrentCustomer(); MapFieldsFromModeltoViewModel(currentCustomer, customerViewModel); return customerViewModel; } public static void MapFieldsFromModeltoViewModel(Customer model, CustomerViewModel viewModel) { viewModel.FirstName = model.FirstName; viewModel.LastName = model.LastName; viewModel.TimeOfMostRecentActivity = model.TimeOfMostRecentActivity; } public static Customer GetCurrentCustomer() { return Customer.GetCurrentCustomer(); } //INotifyPropertyChanged implementation public event PropertyChangedEventHandler PropertyChanged; private void RaisePropertyChanged(string property) { if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(property)); } } } //model public class Customer { public string FirstName { get; set; } public string LastName { get; set; } public DateTime TimeOfMostRecentActivity { get; set; } public static Customer GetCurrentCustomer() { return new Customer { FirstName = "Jim", LastName = "Smith", TimeOfMostRecentActivity = DateTime.Now }; } } }

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  • Dataflow Programming - Patterns and Frameworks

    - by Styrac
    I just came across the proposed Boost::Dataflow library. It seems like an interesting approach and I was wondering if there are other such alternative frameworks for C++, and if there are any related design patterns. I have not ruled out Boost::Dataflow, I am just looking into any available alternatives so I can understand the domain and my options better (or roll my own if necessary).

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  • Best pattern for storing (product) attributes in SQL Server

    - by EdH
    We are starting a new project where we need to store product and many product attributes in a database. The technology stack is MS SQL 2008 and Entity Framework 4.0 / LINQ for data access. The products (and Products Table) are pretty straightforward (a SKU, manufacturer, price, etc..). However there are also many attributes to store with each product (think industrial widgets). These may range from color to certification(s) to pipe size. Every product may have different attributes, and some may have multiples of the same attribute (Ex: Certifications). The current proposal is that we will basically have a name/value pair table with a FK back to the product ID in each row. An example of the attributes Table may look like this: ProdID AttributeName AttributeValue 123 Color Blue 123 FittingSize 1.25 123 Certification AS1111 123 Certification EE2212 123 Certification FM.3 456 Pipe 11 678 Color Red 999 Certification AE1111 ... Note: Attribute name would likely come from a lookup table or enum. So the main question here is: Is this the best pattern for doing something like this? How will the performance be? Queries will be based on a JOIN of the product and attributes table, and generally need many WHEREs to filter on specific attributes - the most common search will be to find a product based on a set of known/desired attributes. If anyone has any suggestions or a better pattern for this type of data, please let me know. Thanks! -Ed

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  • Mindmapping as a Documentation Tool

    - by mcass20
    My team has recently begun using XMind to organize development projects. It seems to be a pretty powerful brainstorming software. I'm just wondering if other developers have employed similar techniques to aid in documenting software design.

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  • Best practice stock management when payment of customer failed using SQL Server and ASP.NET

    - by Martijn B
    Hi there, I am currently building a webshop for my own where I want to increment the product-stock when the user fails to complete payment within 10 minutes after the customer placed the order. I want to gather information from this thread to make a design decision. I am using SQL Server 2008 and ASP.NET 3.5. Should I use a SQL Server Job who intervals check the orders which are not payed yet or are there better solutions to do this. Thanks in advance! Martijn

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  • looking for automated modeling tool for ASP.Net class diagramming

    - by alchemical
    I'm walking into a project with 500+ classes, and am wondering if anyone has had good experiences with automated modeling tools that can import from ASP.Net /C#? It would be a bonus if I could get an automated model based on all the objects called to completely load a single ASP.Net page, with relationships indicating which objects are calling out to which other ones, etc. Thanks for sharing your thoughts or recomendations.

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  • Factory Pattern - when do you say you need a specialised factory

    - by dbones
    Hi, I am having a little design crisis, I am making a Plane class, which is made of an engine 2 wings and N seats The engine takes in a engine size, and the wings have a span. would this still be feasible to have a PlaneFactory, when the factory may have to take in multiple parameters to setup the plane (wings, engine, no of seats) thanks in advance bones

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