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• iOS app with a lot of text

  - by rdurand

  I just asked a question on StackOverflow, but I'm thinking that a part of it belongs here, as questions about design pattern are welcomed by the faq. Here is my situation. I have developed almost completely a native iOS app. The last section I need to implement is all the rules of a sport, so that's a lot of text. It has one main level of sections, divided in subsections, containing a lot of structured text (paragraphs, a few pictures, bulleted/numbered lists, tables). I have absolutely no problem with coding, I'm just looking for advice to improve and make the best design pattern possible for my app. My first shot (the last one so far) was a UITableViewController containing the sections, sending the user to another UITableViewController with the subsections of the selected section, and then one strange last UITableViewController where the cells contain UITextViews, sections header help structure the content, etc. What I would like is your advice on how to improve the structure of this section. I'm perfectly ready to destroy/rebuild the whole thing, I'm really lost in my design here.. As I said on SO, I've began to implement a UIWebView in a UIViewController, showing a html page with JQuery Mobile to display the content, and it's fine. My question is more about the 2 views taking the user to that content. I used UITableViewControllers because that's what seemed the most appropriate for a structured hierarchy like this one. But that doesn't seem like the best solution in term of user experience.. What structure / "view-flow" / kind of presentation would you try to implement in my situation? As always, any help would be greatly appreciated! Just so you can understand better the hierarchy, with a simple example : -----> Section 1 -----> SubSection 1.1 -----> Content | -----> SubSection 1.2 -----> Content | -----> SubSection 1.3 -----> Content | | | UINavigationController -------> Section 2 -----> SubSection 2.1 -----> Content | -----> SubSection 2.2 -----> Content | -----> SubSection 2.3 -----> Content | -----> SubSection 2.4 -----> Content | -----> SubSection 2.5 -----> Content | -----> Section 3 -----> SubSection 3.1 -----> Content -----> SubSection 3.2 -----> Content |------------------| |--------------------| |-------------| 1 UITableViewController 3 UITableViewControllers 10 UIViewControllers (3 rows) (with different with a UIWebView number of rows)

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• "Never do in code what you can get the SQL server to do well for you" - Is this a recipe for a bad design?

  - by PhonicUK

  It's an idea I've heard repeated in a handful of places. Some more or less acknowledging that once trying to solve a problem purely in SQL exceeds a certain level of complexity you should indeed be handling it in code. The logic behind the idea is that for the large majority of cases, the database engine will do a better job at finding the most efficient way of completing your task than you could in code. Especially when it comes to things like making the results conditional on operations performed on the data. Arguably with modern engines effectively JIT'ing + caching the compiled version of your query it'd make sense on the surface. The question is whether or not leveraging your database engine in this way is inherently bad design practice (and why). The lines become blurred further when all the logic exists inside the database and you're just hitting it via an ORM.

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• Separating Db from business with Inherited classes using multiple views

  - by catalinux

  I have a software that has a car model that will be used in different views (listing, ads, detail page, carousel, up sell widget,etc). class CarModel extends DbModel{ } I look for a "nice way" (a combination of flexible, easy to maintain,etc) to have this used in views. I'm thinking at two different ways Having object views for each context CarViewBase{ var car;// of type CarModel function constructor(args){ //will instantienta internal variable car based on args } function getThumb(){ } function getTitle(){ } } CarListingView extends CarViewBase{ function getListing(){ } } CarAdsView extends CarViewBase{ //the busines rule changes for ads widget function getThumb(){ } } Extending directly the CarModel The challenges comes when My Car Model might need an abstract factory. Let's say I have a field on my car object that states the type of the car : a truck, or a bike, or van. How would affect that my object view? Let's say that getTitle() rule would be different for each type of it. How would you do it?

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• How to create a manager class without global variables nor singletons?

  - by Omega

  I would like to implement some kind of manager class in my application. It will be in charge of loading textures, processing them, distributing them etc... At first, I wanted to make a global variable that simply contains an instance of my manager class. I found this question: http://stackoverflow.com/questions/4646577/global-variables-in-java. However, the users there seem to recommend to never use global variables. Fine then, I once heard about Singletons, so I though I could use that instead. I mean, creating just one instance of my manager class sounds good. However, I found this other question: When is Singleton appropriate?, which basically tells me that Singletons are, in most scenarios, some kind of anti-pattern. Now I am a bit lost - what other approach can I take to create my manager class, whose only requirement is to be accessible from anywhere?

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• Dynamic Strategy Pattern [migrated]

  - by Karl Barker

  So I'm writing a web service architecture which includes FunctionProvider classes which do the actual processing of requests, and a main Endpoint class which receives and delegates requests to the proper FunctionProvider. I don't know exactly the FunctionProviders available at runtime, so I need to be able to 'register' (if that's the right word) them with my main Endpoint class, and query them to see if they match an incoming request. public class MyFunc implements FunctionProvider{ static { MyEndpoint.register(MyFunc); } public Boolean matchesRequest(Request req){...} public void processRequest(Request req){...} } public class MyEndpoint{ private static ArrayList<FunctionProvider> functions = new ArrayList<FunctionProvider>(); public void register(Class clz){ functions.add(clz); } public void doPost(Request request){ //find the FunctionProvider in functions //matching the request } } I've really not done much reflective Java like this (and the above is likely wrong, but hopefully demonstrates my intentions). What's the nicest way to implement this without getting hacky?

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• How to separate and maintain customer specific code

  - by WYSIWYG

  I am implementing customer specific code and currently following simple approach like if (cusomterId == 23) do it. I want to separate out all the customer related code in separate place. But I have following problems. In code is in 1. Stored procs 2. Plain old classes. 3. Controllers 4. Views I came up with two solutions. First is to create table CustomerFunctionlity with columns CustomerId, FunctionalityName, method/Proc, inputs/outputs With this table I can simply check if exists, execute given function. Another way is creating a factory which returns customer related object for an interface. I am writting small end to end customer specific functionalities. How can I write maintenable code. Thanks

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• What is the preferred pattern when attaching a 'runtime object'?

  - by sebf

  In my application I have the following: public class NeatObject { /* lots of static data, and configuration flags */ } public class NeatObjectConsumer { void DoCleverStuffWithObjectOnGPU(NeatObject obj); } Where NeatObject and its consumer are used to control the GPU. The idea being that, the configuration of an instance of NeatObject and its members, define how the consumer instance behaves. The object can be passed around, edited, and most importantly serialised/deserialised by the application, with and without knowledge of NeatObjectConsumer, then provided back to the consumer to do something else. The purpose of this seperation is: The consumer manages hardware resources, which change depending on the computer, and even on the execution of the application, making preserving the state of an object which does everything difficult. Avoids circular references if the assembly that contains the consumer needs to reference one that only needs to know about NeatObject. However, there is a complication in that the consumer creates hardware resources and needs to associate them with NeatObject. These don't need to be preserved, but still need to be retrieved. DoCleverStuffWithObjectOnGPU() will be called many, many times during execution and so any bottleneck is a concern, therefore I would like to avoid dictionary lookups. What is the preferred method of attaching this information to NeatObject? By preferred, I mean intuitive - other coders can see immediately what is going on - and robust - method doesn't invite playing with the resources or present them in such a way as to make them easily corruptible. Essentially, I want to add my own metadata - how should I do it? Try to use 'actual metadata' functionality like Reflection? A member of the type of an abstract class? Unmanaged pointers? If you took on a project that used this pattern, what would you have liked the previous developer to do?

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• What Design Pattern is separating transform converters

  - by RevMoon

  For converting a Java object model into XML I am using the following design: For different types of objects (e.g. primitive types, collections, null, etc.) I define each its own converter, which acts appropriate with respect to the given type. This way it can easily extended without adding code to a huge if-else-then construct. The converters are chosen by a method which tests whether the object is convertable at all and by using a priority ordering. The priority ordering is important so let's say a List is not converted by the POJO converter, even though it is convertable as such it would be more appropriate to use the collection converter. What design pattern is that? I can only think of a similarity to the command pattern.

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• Domain Model and Querying

  - by Tyrsius

  I am new to DDD, having worked only in Transaction-Script apps with an anemic model, or just Big Balls of Mud, so please forgive any terminology I abuse. I am trying to understand the proper separation between the domain model and the repository. What is the proper way to construct a domain object that is coming from a database, assuming the (incredibly simplified) need to query for objects by status (returns enumerable), or by ID. Should a factory be building the objects, exposing methods for GetByStatus() and GetByID(), using a DIed repository? Should a repository be called directly, knowing how to build a domain model from the DTO? Should the domain model have a constructor for get by ID, using a DIed repoistory to load the initial state, using some other (?) method for the list? I am not really sure what the best way would be, and this question has an answer advocating each one (these are certainly mutuallu exclusive).

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• Guidelines or Design pattern to develop configurable software

  - by Rumit Parakhiya

  I want to develop an application which would have it's own framework, using which developer can implement functionality very easily. Developer shouldn't have to code for each and every page or report. But, he can do it very easily by just configuring it using the framework provided. Some nice examples of it is SAP and Tally. They have got their own framework, using which anybody having knowledge of it can customize or extend functionality of the product. But, as I am beginner in this direction, I don't have any idea about where to start. Can anybody point me to some design pattern which I can follow or some similar open source software which I can refer?

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• Creating a Predicate Builder extension method

  - by Rippo

  I have a Kendo UI Grid that I am currently allowing filtering on multiple columns. I am wondering if there is a an alternative approach removing the outer switch statement? Basically I want to able to create an extension method so I can filter on a IQueryable<T> and I want to drop the outer case statement so I don't have to switch column names. private static IQueryable<Contact> FilterContactList(FilterDescriptor filter, IQueryable<Contact> contactList) { switch (filter.Member) { case "Name": switch (filter.Operator) { case FilterOperator.StartsWith: contactList = contactList.Where(w => w.Firstname.StartsWith(filter.Value.ToString()) || w.Lastname.StartsWith(filter.Value.ToString()) || (w.Firstname + " " + w.Lastname).StartsWith(filter.Value.ToString())); break; case FilterOperator.Contains: contactList = contactList.Where(w => w.Firstname.Contains(filter.Value.ToString()) || w.Lastname.Contains(filter.Value.ToString()) || (w.Firstname + " " + w.Lastname).Contains( filter.Value.ToString())); break; case FilterOperator.IsEqualTo: contactList = contactList.Where(w => w.Firstname == filter.Value.ToString() || w.Lastname == filter.Value.ToString() || (w.Firstname + " " + w.Lastname) == filter.Value.ToString()); break; } break; case "Company": switch (filter.Operator) { case FilterOperator.StartsWith: contactList = contactList.Where(w => w.Company.StartsWith(filter.Value.ToString())); break; case FilterOperator.Contains: contactList = contactList.Where(w => w.Company.Contains(filter.Value.ToString())); break; case FilterOperator.IsEqualTo: contactList = contactList.Where(w => w.Company == filter.Value.ToString()); break; } break; } return contactList; } Some additional information, I am using NHibernate Linq. Also another problem is that the "Name" column on my grid is actually "Firstname" + " " + "LastName" on my contact entity. We can also assume that all filterable columns will be strings.

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• Hide or Show singleton?

  - by Sinker

  Singleton is a common pattern implemented in both native libraries of .NET and Java. You will see it as such: C#: MyClass.Instance Java: MyClass.getInstance() The question is: when writing APIs, is it better to expose the singleton through a property or getter, or should I hide it as much as possible? Here are the alternatives for illustrative purposes: Exposed(C#): private static MyClass instance; public static MyClass Instance { get { if (instance == null) instance = new MyClass(); return instance; } } public void PerformOperation() { ... } Hidden (C#): private static MyClass instance; public static void PerformOperation() { if (instance == null) { instance = new MyClass(); } ... } EDIT: There seems to be a number of detractors of the Singleton design. Great! Please tell me why and what is the better alternative. Here is my scenario: My whole application utilises one logger (log4net/log4j). Whenever, the program has something to log, it utilises the Logger class (e.g. Logger.Instance.Warn(...) or Logger.Instance.Error(...) etc. Should I use Logger.Warn(...) or Logger.Warn(...) instead? If you have an alternative to singletons that addresses my concern, then please write an answer for it. Thank you :)

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• Is there a pattern to restrict which classes can update another class?

  - by Mike

  Say I have a class ImportantInfo with a public writable property Data. Many classes will read this property but only a few will ever set it. Basically, if you want to update Data you should really know what you're doing. Is there a pattern I could use to make this explicit other than by documenting it? For example, some way to enforce that only classes that implement IUpdateImportantData can do it (this is just an example)? I'm not talking about security here, but more of a "hey, are you sure you want to do that?" kind of thing.

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• Which is a better design pattern for a database wrapper: Save as you go or Save when your done?

  - by izuriel

  I know this is probably a bad way to ask this question. I was unable to find another question that addressed this. The full question is this: We're producing a wrapper for a database and have two different viewpoints on managing data with the wrapper. The first is that all changes made to a data object in code must be persisted in the database by calling a "save" method to actually save the changes. The other side is that these changes should be save as they are made, so if I change a property it's saved, I change another it's save as well. What are the pros/cons of either choice and which is the "proper" way to manage the data?

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• Is it better to return NULL or empty values from functions/methods where the return value is not present?

  - by P B

  I am looking for a recommendation here. I am struggling with whether it is better to return NULL or an empty value from a method when the return value is not present or cannot be determined. Take the following two methods as an examples: string ReverseString(string stringToReverse) // takes a string and reverses it. Person FindPerson(int personID) // finds a Person with a matching personID. In ReverseString(), I would say return an empty string because the return type is string, so the caller is expecting that. Also, this way, the caller would not have to check to see if a NULL was returned. In FindPerson(), returning NULL seems like a better fit. Regardless of whether or not NULL or an empty Person Object (new Person()) is returned the caller is going to have to check to see if the Person Object is NULL or empty before doing anything to it (like calling UpdateName()). So why not just return NULL here and then the caller only has to check for NULL. Does anyone else struggle with this? Any help or insight is appreciated.

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• Why using Fragments?

  - by ahmed_khan_89

  I have read the documentation and some other questions' threads about this topic and I don't really feel convinced; I don't see clearly the limits of use of this technique. Fragments are now seen as a Best Practice; every Activity should be basically a support for one or more Fragments and not call a layout directly. Fragments are created in order to: allow the Activity to use many fragments, to change between them, to reuse these units... == the Fragment is totally dependent to the Context of an activity , so if I need something generic that I can reuse and handle in many Activities, I can create my own custom layouts or Views ... I will not care about this additional Complexity Developing Layer that fragments would add. a better handling to different resolution == OK for tablets/phones in case of long process that we can show two (or more) fragments in the same Activity in Tablets, and one by one in phones. But why would I use fragments always ? handling callbacks to navigate between Fragments (i.e: if the user is Logged-in I show a fragment else I show another fragment). === Just try to see how many bugs facebook SDK Log-in have because of this, to understand that it is really (?) ... considering that an Android Application is based on Activities... Adding another life cycles in the Activity would be better to design an Application... I mean the modules, the scenarios, the data management and the connectivity would be better designed, in that way. === This is an answer of someone who's used to see the Android SDK and Android Framework with a Fragments vision. I don't think it's wrong, but I am not sure it will give good results... And it is really abstract... ==== Why would I complicate my life, coding more, in using them always? else, why is it a best practice if it's just a tool for some cases? what are these cases?

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• Tips for Making this Code Testable [migrated]

  - by Jesse Bunch

  So I'm writing an abstraction layer that wraps a telephony RESTful service for sending text messages and making phone calls. I should build this in such a way that the low-level provider, in this case Twilio, can be easily swapped without having to re-code the higher level interactions. I'm using a package that is pre-built for Twilio and so I'm thinking that I need to create a wrapper interface to standardize the interaction between the Twilio service package and my application. Let us pretend that I cannot modify this pre-built package. Here is what I have so far (in PHP): <?php namespace Telephony; class Provider_Twilio implements Provider_Interface { public function send_sms(Provider_Request_SMS $request) { if (!$request->is_valid()) throw new Provider_Exception_InvalidRequest(); $sms = \Twilio\Twilio::request('SmsMessage'); $response = $sms->create(array( 'To' => $request->to, 'From' => $request->from, 'Body' => $request->body )); if ($this->_did_request_fail($response)) { throw new Provider_Exception_RequestFailed($response->message); } $response = new Provider_Response_SMS(TRUE); return $response; } private function _did_request_fail($api_response) { return isset($api_response->status); } } So the idea is that I can write another file like this for any other telephony service provided that it implements Provider_Interface making them swappable. Here are my questions: First off, do you think this is a good design? How could it be improved? Second, I'm having a hard time testing this because I need to mock out the Twilio package so that I'm not actually depending on Twilio's API for my tests to pass or fail. Do you see any strategy for mocking this out? Thanks in advance for any advice!

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• Moving from mock to real objects?

  - by jjchiw

  I'm like doing TDD so I started everything mocking objects, creating interface, stubbing, great. The design seems to work, now I'll implement the stuff, a lot of the code used in the stubs are going to be reused in my real implementation yay! Now should I duplicate the tests to use the real object implementation (but keeping the mocks object of the sensitive stuff like Database and "services" that are out of my context (http calls, etc...)) Or just change the mocks and stubs of the actual tests to use the real objects....... So the question is that, keep two tests or replace the stubs, mocks? And after that, I should keep designing with the mocks, stubs or just go with real objects? (Just making myself clear I'll keep the mock object of the sensitive stuff like database and services that are out of my context, in both situations.)

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• Best way to load application settings

  - by enzom83

  A simple way to keep the settings of a Java application is represented by a text file with ".properties" extension containing the identifier of each setting associated with a specific value (this value may be a number, string, date, etc..). C# uses a similar approach, but the text file must be named "App.config". In both cases, in source code you must initialize a specific class for reading settings: this class has a method that returns the value (as string) associated with the specified setting identifier. // Java example Properties config = new Properties(); config.load(...); String valueStr = config.getProperty("listening-port"); // ... // C# example NameValueCollection setting = ConfigurationManager.AppSettings; string valueStr = setting["listening-port"]; // ... In both cases we should parse strings loaded from the configuration file and assign the ??converted values to the related typed objects (parsing errors could occur during this phase). After the parsing step, we must check that the setting values ??belong to a specific domain of validity: for example, the maximum size of a queue should be a positive value, some values ??may be related (example: min < max), and so on. Suppose that the application should load the settings as soon as it starts: in other words, the first operation performed by the application is to load the settings. Any invalid values for the settings ??must be replaced automatically with default values??: if this happens to a group of related settings, those settings are all set with default values. The easiest way to perform these operations is to create a method that first parses all the settings, then checks the loaded values ??and finally sets any default values??. However maintenance is difficult if you use this approach: as the number of settings increases while developing the application, it becomes increasingly difficult to update the code. In order to solve this problem, I had thought of using the Template Method pattern, as follows. public abstract class Setting { protected abstract bool TryParseValues(); protected abstract bool CheckValues(); public abstract void SetDefaultValues(); /// <summary> /// Template Method /// </summary> public bool TrySetValuesOrDefault() { if (!TryParseValues() || !CheckValues()) { // parsing error or domain error SetDefaultValues(); return false; } return true; } } public class RangeSetting : Setting { private string minStr, maxStr; private byte min, max; public RangeSetting(string minStr, maxStr) { this.minStr = minStr; this.maxStr = maxStr; } protected override bool TryParseValues() { return (byte.TryParse(minStr, out min) && byte.TryParse(maxStr, out max)); } protected override bool CheckValues() { return (0 < min && min < max); } public override void SetDefaultValues() { min = 5; max = 10; } } The problem is that in this way we need to create a new class for each setting, even for a single value. Are there other solutions to this kind of problem? In summary: Easy maintenance: for example, the addition of one or more parameters. Extensibility: a first version of the application could read a single configuration file, but later versions may give the possibility of a multi-user setup (admin sets up a basic configuration, users can set only certain settings, etc..). Object oriented design.

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• Legal Applications of Metamorphic Code

  - by V_P

  Firstly, I would like to state that I already understand the 'vx' applications for Metamorphic code. I am not here to ask a question related to any of those topics as that would be inappropriate in this context. I would like to know if anyone has ever used 'Metamorphic' code in practice, for purposes other than those previously stated, if so, what was the reasoning for using said concept. In essence I am trying to discover a purpose for this concept, if any, other than circumventing anti-virus scanners and the like.

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• How can I refactor my code to use fewer singletons?

  - by fish

  I started a component based, networked game (so far only working on the server). I know why singletons can be bad, but I can't think of another way to implement the same thing. So far I have: A GameState singleton (for managing the global state of the game, i.e. pre-game, running, exiting). A World singleton, which is the root entity for my entity graph An EntityFactory A ComponentFactory I'm thinking about adding a "MessageDispatcher" so individual components can subscribe to network messages. The factories do not have state, so I suppose they aren't so bad. However, the others do have global state, which is asking for trouble. How can I refactor my code so it uses fewer singletons?

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• Recommended design pattern for object with optional and modifiable attributtes? [on hold]

  - by Ikuzen

  I've been using the Builder pattern to create objects with a large number of attributes, where most of them are optional. But up until now, I've defined them as final, as recommended by Joshua Block and other authors, and haven't needed to change their values. I am wondering what should I do though if I need a class with a substantial number of optional but non-final (mutable) attributes? My Builder pattern code looks like this: public class Example { //All possible parameters (optional or not) private final int param1; private final int param2; //Builder class public static class Builder { private final int param1; //Required parameters private int param2 = 0; //Optional parameters - initialized to default //Builder constructor public Builder (int param1) { this.param1 = param1; } //Setter-like methods for optional parameters public Builder param2(int value) { param2 = value; return this; } //build() method public Example build() { return new Example(this); } } //Private constructor private Example(Builder builder) { param1 = builder.param1; param2 = builder.param2; } } Can I just remove the final keyword from the declaration to be able to access the attributes externally (through normal setters, for example)? Or is there a creational pattern that allows optional but non-final attributes that would be better suited in this case?

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• In some games, we just let the main() loop be the Player object or Table object?

  - by ????

  I was thinking that let's say if there is a game of Blackjack or MasterMind, then we should have a class called Dealer or ComputerPal, which is how the computer interact with us (as a dealer for Blackjack or as the person giving hints for MasterMind). And then there should be a Player object, and the way to play one game is aPlayer.playGame but I noticed that a book was just using the main() loop to act as the player (or as the Controller of the game), calling the Dealer methods to dealer the cards, ask for player's action, etc... 1) Is this just a lazy way to model all the proper objects? 2) If more objects are to be added, who should call the aDealer.dealCards and then ask for aPlayer.askForAction? (because it is strange to let the Player handle all the logical steps). Should there be a Table object that handle all these logic and then to play one round of game, use aTable.playGame? What is a good object design for such game?

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• Name for this antipattern? Fields as local variables

  - by JSB????

  In some code I'm reviewing, I'm seeing stuff that's the moral equivalent of the following: public class Foo { private Bar bar; public MethodA() { bar = new Bar(); bar.A(); bar = null; } public MethodB() { bar = new Bar(); bar.B(); bar = null; } } The field bar here is logically a local variable, as its value is never intended to persist across method calls. However, since many of the methods in Foo need an object of type Bar, the original code author has just made a field of type Bar. This is obviously bad, right? Is there a name for this antipattern?

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• If an entity is composed, is it still a god object?

  - by Telastyn

  I am working on a system to configure hardware. Unfortunately, there is tons of variety in the hardware, which means there's a wide variety of capabilities and configurations depending on what specific hardware the software connects to. To deal with this, we're using a Component Based Entity design where the "hardware" class itself is a very thin container for components that are composed at runtime based on what capabilities/configuration are available. This works great, and the design itself has worked well elsewhere (particularly in games). The problem is that all this software does is configure the hardware. As such, almost all of the code is a component of the hardware instance. While the consumer only ever works against the strongly typed interfaces for the components, it could be argued that the class that represents an instance of the hardware is a God Object. If you want to do anything to/with the hardware, you query an interface and work with it. So, even if the components of an object are modular and decoupled well, is their container a God Object and the downsides associated with the anti-pattern?

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