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• ASP.net SessionState Error in Design Mode

  - by stringo0

  I'm getting a weird error in the design view for a user creation page for 2 controls: Error Creating Control - wCreateUser Session state can only be used when enableSessionState is set to true, either in a configuration file or in the Page directive. (There's some more) I've done both of these, but I'm still getting the error in design mode. The controls work fine when compiled, and on the live site - this is just in the Visual Web Developer 2010 Design view for the page. Any ideas as to how I can resolve this? Thanks!

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• Facing problem in VB6.0 Activex Controls design.

  - by Dharmaraju

  Hi, This is dharmaraju, I am facing some problem in Activex Controls design. Kindly help me to resolve the issue. Problem Description: I have created a property mentioned below for a textbox. Public Property Let DataControl_Value(ByVal Value As Variant) Public Property Get DataControl_Value() As Variant This property is editable at design time if i use it VB6.0 Applications. Same thing is read only in case if i use it in vc++ MFC applications. I have defined one more property like below. Public Property Let DataControl_DataItemDef(ByVal Value As DTMDATACONTROLLib.IXMLDOMNode) Public Property Get DataControl_DataItemDef() As DTMDATACONTROLLib.IXMLDOMNode In this case the "DataControl_DataItemDef" property will not be available at design time.[not displaying in control's property window.] Kindly help me to resolve the issue.

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• Need help in Architecture design in java

  - by palakolanusrinu

  Can anyone help in architecture design of one of my complex application. Requirement : In web based application, we need to generate Excel kind of report as HTML page and after that we need to perform different kinds of operations like Add manual rows Delete rows Edit rows adding comments based on each cell viewing the added comments. attaching the file based on each cell viewing the attached file. Collapsible functionality for some of rows In the process of design we have come up with DB design and application framework is Spring. and for Web not yet finalized. what is the best approach to implement this kind of UI? --JSF?(keep in mind we need to Excel operations like above mentioned operations) -- Any reporting tool which will provide editing functionality? Please suggest me How can we do it? and what is the best technology for it? or is there any reporting tools?

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• Custom UI design in Sencha and othere touch framworks

  - by vWebby

  Can someone please guide me regarding which touch framework (javascript) I should use to make a tablet app? I am new to this area and I am looking for something which allows me to play with my own UI design comfortably. I went through sencha as I heard its apt for a tablet app environment but I am (sorry, it might sound odd) not able to make out whether I can use my own UI design to make app in sencha. Or any other framework (stable) allows to use custom UI design?? Any help regarding this is appreciated .. thanks in advance

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• JTable Design Guide in Swing Application

  - by zwang

  I have a really hard design problem in my swing application. Generally Speaking, I have a JTable and a JLabel to display. The label is right below the JTable. When the height of these two components doesn't exceed a threshold, then the jtable and label displays as normal. Then height of these two components will increase as the number of records filled in the table increases. When the height of these two components exceeds a threshold, I want there is a scrollbar in the JTable and the height of these two components will be the threshold. Is this design Possible? I have draft to illustate my UI design requirement. But I don't know how to post it in this forum. And any reply are appreciate. Best Regards, Zheng.

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• Designing an email system to guarantee delivery

  - by GlenH7

  We are looking to expand our use of email for notification purposes. We understand it will generate more inbox volume, but we are being selective about which events we fire notification on in order to keep the signal-to-noise ratio high. The big question we are struggling with is designing a system that guarantees that the email was delivered. If an email isn't delivered, we will consider that an exception event that needs to be investigated. In reality, I say almost guarantees because there aren't any true guarantees with email. We're just looking for a practical solution to making sure the email got there and experiences others have had with the various approaches to guaranteeing delivery. For the TL;DR crowd - how do we go about designing a system to guarantee delivery of emails? What techniques should we consider so we know the emails were delivered? Our biggest area of concern is what techniques to use so that we know when a message is sent out that it either lands in an inbox or it failed and we need to do something else. Additional requirements: We're not at the stage of including an escalation response, but we'll want that in the future or so we think. Most notifications will be internal to our enterprise, but we will have some notifications being sent to external clients. Some of our application is in a hosted environment. We haven't determined if those servers can access our corporate email servers for relaying or if they'll be acting as their own mail servers. Base design / modules (at the moment): A module to assign tracking identification A module to send out emails A module to receive delivery notification (perhaps this is the same as the email module) A module that checks sent messages against delivery notification and alerts on undelivered email. Some references: Atwood: Send some email Email Tracking Some approaches: Request a response (aka read-receipt or Message Disposition Notification). Seems prone to failure since we have cross-compatibility issues due to differing mail servers and software. Return receipt (aka Delivery Status Notification). Not sure if all mail servers honor this request or not Require an action and therefore prove reply. Seems burdensome to force the recipients to perform an additional task not related to resolving the issue. And no, we haven't come up with a way of linking getting the issue fixed to whether or not the email was received. Force a click-through / Other site sign-in. Similar to requiring some sort of action, this seems like an additional burden and will annoy the users. On the other hand, it seems the most likely to guarantee someone received the notification. Hidden image tracking. Not all email providers automatically load the image, and how would we associate the image(s) with the email tracking ID? Outsource delivery. This gets us out of the email business, but goes back to how to guarantee the out-sourcer's receipt and subsequent delivery to the end recipient. As a related concern, there will be an n:n relationship between issue notification and recipients. The 1 issue : n recipients subset isn't as much of a concern although if we had a delivery failure we would want to investigate and fix the core issue. Of bigger concern is n issues : 1 recipient, and we're specifically concerned in making sure that all n issues were received by the recipient. How does forum software or issue tracking software handle this requirement? If a tracking identifier is used, Where is it placed in the email? In the Subject, or the Body?

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• Footer not stretching 100% when horizontally scrolled

  - by Dan

  I have a footer which is set to 100% width, but if i size the window smaller so a horizontal scrollbar appears, using the scrollbar shows whitespace to the right of the footer ... its not spanned 100% of the page, just the viewport. <!doctype html> <html lang="en" class="no-js"> <head> <title>test</title> <meta charset="utf-8"> </head> <body> <div id="container" style="width:100%"> <div id="body" style="width:1200px;"> <!-- Body start --> <h1>Main content area</h1> <p>Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh. Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh. Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh. Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh. Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh.</p> <p>Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh. Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh. Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh. Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh. Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh.</p> <p>Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh. Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh. Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh. Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh. Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh.</p> <!-- Body end --> </div> <div id="footer" style="width:100%; background-color:green;"> <!-- Footer start --> <p><b>FOOTER.</b> Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh. Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh. Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh. Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh. Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh.</p> <!-- Footer end --> </div> </div> </body> </html> Size the browser so horizontal scrollbar appears, and then scroll and you will see the footer background just stops. Any ideas? Or is this site the wrong place for web site design/development .. I did have to read the site description but it still wasnt clear, nor was the meta-discussion? Apologies if its in the wrong place.

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• The Oracle Retail Week Awards - most exciting awards yet?

  - by sarah.taylor(at)oracle.com

  Last night's annual Oracle Retail Week Awards saw the UK's top retailers come together to celebrate the very best of our industry over the last year.  The Grosvenor House Hotel on Park Lane in London was the setting for an exciting ceremony which this year marked several significant milestones in British - and global - retail.  Check out our videos about the event at our Oracle Retail YouTube channel, and see if you were snapped by our photographer on our Oracle Retail Facebook page. There were some extremely hot contests for many of this year's awards - and all very deserving winners.  The entries have demonstrated beyond doubt that retailers have striven to push their standards up yet again in all areas over the past year.  The judging panel includes some of the most prestigious names in the retail industry - to impress the panel enough to win an award is a substantial achievement.  This year the panel included the likes of Andy Clarke - Chief Executive of ASDA Group; Mark Newton Jones - CEO of Shop Direct Group; Richard Pennycook - the finance director at Morrisons; Rob Templeman - Chief Executive of Debenhams; and Stephen Sunnucks - the president of Gap Europe.  These are retail veterans  who have each helped to shape the British High Street over the last decade.  It was great to chat with many of them in the Oracle VIP area last night.  For me, last night's highlight was honouring both Sir Stuart Rose and Sir Terry Leahy for their contributions to the retail industry.  Both have set the standards in retailing over the last twenty years and taken their respective businesses from strength to strength, demonstrating that there is always a need for innovation even in larger businesses, and that a business has to adapt quickly to new technology in order to stay competitive.  Sir Terry Leahy's retirement this year marks the end of an era of global expansion for the Tesco group and a milestone in the progression of British retail.  Sir Terry has helped steer Tesco through nearly 20 years of change, with 14 years as Chief Executive.  During this time he led the drive for international expansion and an aggressive campaign to increase market share.  He has led the way for High Street retailers in adapting to the rise of internet retailing and nurtured a very successful home delivery service.  More recently he has pioneered the notion of cross-channel retailing with the introduction of Tesco apps for the iPhone and Android mobile phones allowing customers to scan barcodes of items to add to a shopping list which they can then either refer to in store or order for delivery.  John Lewis Partnership was a very deserving winner of The Oracle Retailer of the Year award for their overall dedication to excellent retailing practices.  The business was also named the American Express Marketing/Advertising Campaign of the Year award for their memorable 'Never Knowingly Undersold' advert series, which included a very successful viral video and radio campaign with Fyfe Dangerfield's cover of Billy Joel's 'She's Always a Woman' used for the adverts.  Store Design of the Year was another exciting category with Topshop taking the accolade for its flagship Oxford Street store in London, which combines boutique concession-style stalls with high fashion displays and exclusive collections from leading designers.  The store even has its own hairdressers and food hall, making it a truly all-inclusive fashion retail experience and a global landmark for any self-respecting international fashion shopper. Over the next few weeks we'll be exploring some of the winning entries in more detail here on the blog, so keep an eye out for some unique insights into how the winning retailers have made such remarkable achievements. 

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• How would you gather client's data on Google App Engine without using Datastore/Backend Instances too much?

  - by ruslan

  I'm relatively new to StackExchange and not sure if it's appropriate place to ask design question. Site gives me a hint "The question you're asking appears subjective and is likely to be closed". Please let me know. Anyway.. One of the projects I'm working on is online survey engine. It's my first big commercial project on Google App Engine. I need your advice on how to collect stats and efficiently record them in DataStore without bankrupting me. Initial requirements are: After user finishes survey client sends list of pairs [ID (int) + PercentHit (double)]. This list shows how close answers of this user match predefined answers of reference answerers (which identified by IDs). I call them "target IDs". Creator of the survey wants to see aggregated % for given IDs for last hour, particular timeframe or from the beginning of the survey. Some surveys may have thousands of target/reference answerers. So I created entity public class HitsStatsDO implements Serializable { @Id transient private Long id; transient private Long version = (long) 0; transient private Long startDate; @Parent transient private Key parent; // fake parent which contains target id @Transient int targetId; private double avgPercent; private long hitCount; } But writing HitsStatsDO for each target from each user would give a lot of data. For instance I had a survey with 3000 targets which was answered by ~4 million people within one week with 300K people taking survey in first day. Even if we assume they were answering it evenly for 24 hours it would give us ~1040 writes/second. Obviously it hits concurrent writes limit of Datastore. I decided I'll collect data for one hour and save that, that's why there are avgPercent and hitCount in HitsStatsDO. GAE instances are stateless so I had to use dynamic backend instance. There I have something like this: // Contains stats for one hour private class Shard { ReadWriteLock lock = new ReentrantReadWriteLock(); Map<Integer, HitsStatsDO> map = new HashMap<Integer, HitsStatsDO>(); // Key is target ID public void saveToDatastore(); public void updateStats(Long startDate, Map<Integer, Double> hits); } and map with shard for current hour and previous hour (which doesn't stay here for long) private HashMap<Long, Shard> shards = new HashMap<Long, Shard>(); // Key is HitsStatsDO.startDate So once per hour I dump Shard for previous hour to Datastore. Plus I have class LifetimeStats which keeps Map<Integer, HitsStatsDO> in memcached where map-key is target ID. Also in my backend shutdown hook method I dump stats for unfinished hour to Datastore. There is only one major issue here - I have only ONE backend instance :) It raises following questions on which I'd like to hear your opinion: Can I do this without using backend instance ? What if one instance is not enough ? How can I split data between multiple dynamic backend instances? It hard because I don't know how many I have because Google creates new one as load increases. I know I can launch exact number of resident backend instances. But how many ? 2, 5, 10 ? What if I have no load at all for a week. Constantly running 10 backend instances is too expensive. What do I do with data from clients while backend instance is dead/restarting? Thank you very much in advance for your thoughts.

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• Method flags as arguments or as member variables?

  - by Martin

  I think the title "Method flags as arguments or as member variables?" may be suboptimal, but as I'm missing any better terminology atm., here goes: I'm currently trying to get my head around the problem of whether flags for a given class (private) method should be passed as function arguments or via member variable and/or whether there is some pattern or name that covers this aspect and/or whether this hints at some other design problems. By example (language could be C++, Java, C#, doesn't really matter IMHO): class Thingamajig { private ResultType DoInternalStuff(FlagType calcSelect) { ResultType res; for (... some loop condition ...) { ... if (calcSelect == typeA) { ... } else if (calcSelect == typeX) { ... } else if ... } ... return res; } private void InteralStuffInvoker(FlagType calcSelect) { ... DoInternalStuff(calcSelect); ... } public void DoThisStuff() { ... some code ... InternalStuffInvoker(typeA); ... some more code ... } public ResultType DoThatStuff() { ... some code ... ResultType x = DoInternalStuff(typeX); ... some more code ... further process x ... return x; } } What we see above is that the method InternalStuffInvoker takes an argument that is not used inside this function at all but is only forwarded to the other private method DoInternalStuff. (Where DoInternalStuffwill be used privately at other places in this class, e.g. in the DoThatStuff (public) method.) An alternative solution would be to add a member variable that carries this information: class Thingamajig { private ResultType DoInternalStuff() { ResultType res; for (... some loop condition ...) { ... if (m_calcSelect == typeA) { ... } ... } ... return res; } private void InteralStuffInvoker() { ... DoInternalStuff(); ... } public void DoThisStuff() { ... some code ... m_calcSelect = typeA; InternalStuffInvoker(); ... some more code ... } public ResultType DoThatStuff() { ... some code ... m_calcSelect = typeX; ResultType x = DoInternalStuff(); ... some more code ... further process x ... return x; } } Especially for deep call chains where the selector-flag for the inner method is selected outside, using a member variable can make the intermediate functions cleaner, as they don't need to carry a pass-through parameter. On the other hand, this member variable isn't really representing any object state (as it's neither set nor available outside), but is really a hidden additional argument for the "inner" private method. What are the pros and cons of each approach?

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• Designing An ACL Based Permission System

  - by ryanzec

  I am trying to create a permissions system where everything is going to be stored in MySQL (or some database) and pulled using PHP for a project management system I am building.  I am right now trying to do it is an ACL kind of way.  There are a number key features I want to be able to support: 1.  Being able to assign permissions without being tied to a specific object. The reason for this is that I want to be able to selectively show/hide elements of the UI based on permissions at a point where I am not directly looking at a domain object instance.  For instance, a button to create a new project should only should only be shown to users that have the pm.project.create permission but obviously you can assign a create permission to an domain object instance (as it is already created). 2.  Not have to assign permissions for every single object. Obviously creating permissions entries for every single object (projects, tickets, comments, etc…) would become a nightmare to maintain so I want to have some level of permission inheritance. *3.  Be able to filter queries based on permissions. This would be a really nice to have but I am not sure if it is possible.  What I mean by this is say I have a page that list all projects.  I want the query that pulls all projects to incorporate the ACL so that it would not show projects that the current user does not have pm.project.read access to.  This would have to be incorporated into the main query as if it is a process that is done after that main query (which I know I could do) certain features like pagination become much more difficult. Right now this is my basic design for the tables: AclEntities id - the primary key key - the unique identifier for the domain object (usually the primary key of that object) parentId - the parent of the domain object (like the project object if this was a ticket object) aclDomainObjectId - metadata about the domain object AclDomainObjects id - primary key title - simple string to unique identify the domain object(ie. project, ticket, comment, etc…) fullyQualifiedClassName - the fully qualified class name for use in code (I am using namespaces) There would also be tables mapping AclEntities to Users and UserGroups. I also have this interface that all acl entity based object have to implement: IAclEntity getAclKey() - to the the unique key for this specific instance of the acl domain object (generally return the primary key or a concatenated string of a composite primary key) getAclTitle() - to get the unique title for the domain object (generally just returning a static string) getAclDisplayString() - get the string that represents this entity (generally one or more field on the object) getAclParentEntity() - get the parent acl entity object (or null if no parent) getAclEntity() - get the acl enitty object for this instance of the domain object (or null if one has not been created yet) hasPermission($permissionString, $user = null) - whether or not the user has the permission for this instance of the domain object static getFromAclEntityId($aclEntityId) - get a specific instance of the domain object from an acl entity id. Do any of these features I am looking for seems hard to support or are just way off base? Am I missing or not taking in account anything in my implementation? Is performance something I should keep in mind?

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• Would this be a good web application architecture?

  - by Gustav Bertram

  My problem Our MVC based framework does not allow us to cache only part of our output. Ideally we want to cahce static and semi-static bits, and run dynamic bits. In addition, we need to consider data caching that reacts to database changes. My idea The concept I came up with was to represent a page as a tree of XML fragment objects. (I say XML, but I mean XHTML). Some of the fragments are dynamic, and can pull their data directly from models or other sources, but most of the fragments are static scaffolding. If a subtree of fragments is completely static, then I imagine that they could unfold into pure XML that would then be cached as the text representation of their parent element. This process would ideally continue until we are left with a root element that contains all of the static XML, and has a couple of dynamic XML fragments that are resolved and attached to the relevant nodes of the XML tree just before the page is displayed. In addition to separating content into dynamic and static fragments, some fragments could be dynamic and cached. A simple expiry time which propagates up through the XML fragment tree would indicate that a specific fragment should periodically be refreshed. A newspaper section or front page does not need to be updated each second. Minutes or sometimes even longer is sufficient. Other fragments would be dynamic and uncached. Typically too many articles are viewed for them to be cached - the cache would overflow. Some individual articles may be cached if they are extremely popular. Functional notes The folding mechanism could be to be smart enough to judge when it would be more profitable to fold a dynamic cached fragment and propagate the expiry date to the parent fragment, or to keep it separate and simple attach to the XML tree when resolving the page. If some dynamic cached fragments are associated to database objects through mechanisms like a globally unique content id, then changes to the database could trigger changes to the output cache. If fragments store the identifiers of parent fragments, then they could trigger a refolding process that would then include the updated data. A set of pure XML with an ordered array of fragment objects (that each store the identifying information of the node to which they should be attached), can be resolved in a fairly simple way by walking the XML tree, and merging the data from the fragments. Because it is not necessary to parse and construct the entire tree in memory before attaching nodes, processing should be fairly fast. The identifiers of each fragment would be a combination of relevant identity data and the type of fragment object. Cached parent fragments would contain references to these identifiers, in order to then either pull them from the fragment cache, or to run their code. The controller's responsibility is reduced to making changes to the database, and telling the root XML fragment object to render itself. The Question My question has two parts: Is this a good design? Are there any obvious flaws I'm missing? Has somebody else thought of this before? References? Is there an existing alternative that I should consider? A cool templating engine maybe?

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• Use a custom value object or a Guid as an entity identifier in a distributed system?

  - by Kazark

  tl;dr I've been told that in domain-driven design, an identifier for an entity could be a custom value object, i.e. something other than Guid, string, int, etc. Can this really be advisable in a distributed system? Long version I will invent an situation analogous to the one I am currently facing. Say I have a distributed system in which a central concept is an egg. The system allows you to order eggs and see spending reports and inventory-centric data such as quantity on hand, usage, valuation and what have you. There area variety of services backing these behaviors. And say there is also another app which allows you to compose recipes that link to a particular egg type. Now egg type is broken down by the species—ostrich, goose, duck, chicken, quail. This is fine and dandy because it means that users don't end up with ostrich eggs when they wanted quail eggs and whatnot. However, we've been getting complaints because jumbo chicken eggs are not even close to equivalent to small ones. The price is different, and they really aren't substitutable in recipes. And here we thought we were doing users a favor by not overwhelming them with too many options. Currently each of the services (say, OrderSubmitter, EggTypeDefiner, SpendingReportsGenerator, InventoryTracker, RecipeCreator, RecipeTracker, or whatever) are identifying egg types with an industry-standard integer representation the species (let's call it speciesCode). We realize we've goofed up because this change could effect every service. There are two basic proposed solutions: Use a predefined identifier type like Guid as the eggTypeID throughout all the services, but make EggTypeDefiner the only service that knows that this maps to a speciesCode and eggSizeCode (and potentially to an isOrganic flag in the future, or whatever). Use an EggTypeID value object which is a combination of speciesCode and eggSizeCode in every service. I've proposed the first solution because I'm hoping it better encapsulates the definition of what an egg type is in the EggTypeDefiner and will be more resilient to changes, say if some people now want to differentiate eggs by whether or not they are "organic". The second solution is being suggested by some people who understand DDD better than I do in the hopes that less enrichment and lookup will be necessary that way, with the justification that in DDD using a value object as an ID is fine. Also, they are saying that EggTypeDefiner is not a domain and EggType is not an entity and as such should not have a Guid for an ID. However, I'm not sure the second solution is viable. This "value object" is going to have to be serialized into JSON and URLs for GET requests and used with a variety of technologies (C#, JavaScript...) which breaks encapsulation and thus removes any behavior of the identifier value object (is either of the fields optional? etc.) Is this a case where we want to avoid something that would normally be fine in DDD because we are trying to do DDD in a distributed fashion? Summary Can it be a good idea to use a custom value object as an identifier in a distributed system (solution #2)?

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• Is my class structure good enough?

  - by Rivten

  So I wanted to try out this challenge on reddit which is mostly about how you structure your data the best you can. I decided to challenge my C++ skills. Here's how I planned this. First, there's the Game class. It deals with time and is the only class main has access to. A game has a Forest. For now, this class does not have a lot of things, only a size and a Factory. Will be put in better use when it will come to SDL-stuff I guess A Factory is the thing that deals with the Game Objects (a.k.a. Trees, Lumberjack and Bears). It has a vector of all GameObjects and a queue of Events which will be managed at the end of one month. A GameObject is an abstract class which can be updated and which can notify the Event Listener The EventListener is a class which handles all the Events of a simulation. It can recieve events from a Game Object and notify the Factory if needed, the latter will manage correctly the event. So, the Tree, Lumberjack and Bear classes all inherits from GameObject. And Sapling and Elder Tree inherits from Tree. Finally, an Event is defined by an event_type enumeration (LUMBERJACK_MAWED, SAPPLING_EVOLUTION, ...) and an event_protagonists union (a GameObject or a pair of GameObject (who killed who ?)). I was quite happy at first with this because it seems quite logic and flexible. But I ended up questionning this structure. Here's why : I dislike the fact that a GameObject need to know about the Factory. Indeed, when a Bear moves somewhere, it needs to know if there's a Lumberjack ! Or it is the Factory which handles places and objects. It would be great if a GameObject could only interact with the EventListener... or maybe it's not that much of a big deal. Wouldn't it be better if I separate the Factory in three vectors ? One for each kind of GameObject. The idea would be to optimize research. If I'm looking do delete a dead lumberjack, I would only have to look in one shorter vector rather than a very long vector. Another problem arises when I want to know if there is any particular object in a given case because I have to look for all the gameObjects and see if they are at the given case. I would tend to think that the other idea would be to use a matrix but then the issue would be that I would have empty cases (and therefore unused space). I don't really know if Sapling and Elder Tree should inherit from Tree. Indeed, a Sapling is a Tree but what about its evolution ? Should I just delete the sapling and say to the factory to create a new Tree at the exact same place ? It doesn't seem natural to me to do so. How could I improve this ? Is the design of an Event quite good ? I've never used unions before in C++ but I didn't have any other ideas about what to use. Well, I hope I have been clear enough. Thank you for taking the time to help me !

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• Writing a method to 'transform' an immutable object: how should I approach this?

  - by Prog

  (While this question has to do with a concrete coding dilemma, it's mostly about what's the best way to design a function.) I'm writing a method that should take two Color objects, and gradually transform the first Color into the second one, creating an animation. The method will be in a utility class. My problem is that Color is an immutable object. That means that I can't do color.setRGB or color.setBlue inside a loop in the method. What I can do, is instantiate a new Color and return it from the method. But then I won't be able to gradually change the color. So I thought of three possible solutions: 1- The client code includes the method call inside a loop. For example: int duration = 1500; // duration of the animation in milliseconds int steps = 20; // how many 'cycles' the animation will take for(int i=0; i<steps; i++) color = transformColor(color, targetColor, duration, steps); And the method would look like this: Color transformColor(Color original, Color target, int duration, int steps){ int redDiff = target.getRed() - original.getRed(); int redAddition = redDiff / steps; int newRed = original.getRed() + redAddition; // same for green and blue .. Thread.sleep(duration / STEPS); // exception handling omitted return new Color(newRed, newGreen, newBlue); } The disadvantage of this approach is that the client code has to "do part of the method's job" and include a for loop. The method doesn't do it's work entirely on it's own, which I don't like. 2- Make a mutable Color subclass with methods such as setRed, and pass objects of this class into transformColor. Then it could look something like this: void transformColor(MutableColor original, Color target, int duration){ final int STEPS = 20; int redDiff = target.getRed() - original.getRed(); int redAddition = redDiff / steps; int newRed = original.getRed() + redAddition; // same for green and blue .. for(int i=0; i<STEPS; i++){ original.setRed(original.getRed() + redAddition); // same for green and blue .. Thread.sleep(duration / STEPS); // exception handling omitted } } Then the calling code would usually look something like this: // The method will usually transform colors of JComponents JComponent someComponent = ... ; // setting the Color in JComponent to be a MutableColor Color mutableColor = new MutableColor(someComponent.getForeground()); someComponent.setForeground(mutableColor); // later, transforming the Color in the JComponent transformColor((MutableColor)someComponent.getForeground(), new Color(200,100,150), 2000); The disadvantage is - the need to create a new class MutableColor, and also the need to do casting. 3- Pass into the method the actual mutable object that holds the color. Then the method could do object.setColor or similar every iteration of the loop. Two disadvantages: A- Not so elegant. Passing in the object that holds the color just to transform the color feels unnatural. B- While most of the time this method will be used to transform colors inside JComponent objects, other kinds of objects may have colors too. So the method would need to be overloaded to receive other types, or receive Objects and have instanceof checks inside.. Not optimal. Right now I think I like solution #2 the most, than solution #1 and solution #3 the least. However I'd like to hear your opinions and suggestions regarding this.

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• Why is 0 false?

  - by Morwenn

  This question may sound dumb, but why does 0 evaluates to false and any other [integer] value to true is most of programming languages? String comparison Since the question seems a little bit too simple, I will explain myself a little bit more: first of all, it may seem evident to any programmer, but why wouldn't there be a programming language - there may actually be, but not any I used - where 0 evaluates to true and all the other [integer] values to false? That one remark may seem random, but I have a few examples where it may have been a good idea. First of all, let's take the example of strings three-way comparison, I will take C's strcmp as example: any programmer trying C as his first language may be tempted to write the following code: if (strcmp(str1, str2)) { // Do something... } Since strcmp returns 0 which evaluates to false when the strings are equal, what the beginning programmer tried to do fails miserably and he generally does not understand why at first. Had 0 evaluated to true instead, this function could have been used in its most simple expression - the one above - when comparing for equality, and the proper checks for -1 and 1 would have been done only when needed. We would have considered the return type as bool (in our minds I mean) most of the time. Moreover, let's introduce a new type, sign, that just takes values -1, 0 and 1. That can be pretty handy. Imagine there is a spaceship operator in C++ and we want it for std::string (well, there already is the compare function, but spaceship operator is more fun). The declaration would currently be the following one: sign operator<=>(const std::string& lhs, const std::string& rhs); Had 0 been evaluated to true, the spaceship operator wouldn't even exist, and we could have declared operator== that way: sign operator==(const std::string& lhs, const std::string& rhs); This operator== would have handled three-way comparison at once, and could still be used to perform the following check while still being able to check which string is lexicographically superior to the other when needed: if (str1 == str2) { // Do something... } Old errors handling We now have exceptions, so this part only applies to the old languages where no such thing exist (C for example). If we look at C's standard library (and POSIX one too), we can see for sure that maaaaany functions return 0 when successful and any integer otherwise. I have sadly seen some people do this kind of things: #define TRUE 0 // ... if (some_function() == TRUE) { // Here, TRUE would mean success... // Do something } If we think about how we think in programming, we often have the following reasoning pattern: Do something Did it work? Yes -> That's ok, one case to handle No -> Why? Many cases to handle If we think about it again, it would have made sense to put the only neutral value, 0, to yes (and that's how C's functions work), while all the other values can be there to solve the many cases of the no. However, in all the programming languages I know (except maybe some experimental esotheric languages), that yes evaluates to false in an if condition, while all the no cases evaluate to true. There are many situations when "it works" represents one case while "it does not work" represents many probable causes. If we think about it that way, having 0 evaluate to true and the rest to false would have made much more sense. Conclusion My conclusion is essentially my original question: why did we design languages where 0 is false and the other values are true, taking in account my few examples above and maybe some more I did not think of? Follow-up: It's nice to see there are many answers with many ideas and as many possible reasons for it to be like that. I love how passionate you seem to be about it. I originaly asked this question out of boredom, but since you seem so passionate, I decided to go a little further and ask about the rationale behind the Boolean choice for 0 and 1 on Math.SE :)

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• What should be the responsibility of a presenter here?

  - by Achu

  I have a 3 layer design. (UI / BLL / DAL) UI = ASP.NET MVC In my view I have collection of products for a category. Example: Product 1, Product 2 etc.. A user able to select or remove (by selecting check box) product’s from the view, finally save as a collection when user submit these changes. With this 3 layer design how this product collection will be saved? How the filtering of products (removal and addition) to the category object? Here are my options. (A) It is the responsibility of the controller then the pseudo Code would be Find products that the user selected or removed and compare with existing records. Add or delete that collection to category object. Call SaveCategory(category); // BLL CALL Here the first 2 process steps occurs in the controller. (B) It is the responsibility of BLL then pseudo Code would be Collect products what ever user selected SaveCategory(category, products); // BLL CALL Here it's up to the SaveCategory (BLL) to decide what products should be removed and added to the database. Thanks

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• Moq and accessing called parameters

  - by lozzar

  I've just started to implement unit tests (using xUnit and Moq) on an already established project of mine. The project extensively uses dependency injection via the unity container. I have two services A and B. Service A is the one being tested in this case. Service A calls B and gives it a delegate to an internal function. This 'callback' is used to notify A when a message has been received that it must handle. Hence A calls (where b is an instance of service B): b.RegisterHandler(Guid id, Action<byte[]> messageHandler); In order to test service A, I need to be able to call messageHandler, as this is the only way it currently accepts messages. Can this be done using Moq? ie. Can I mock service B, such that when RegisterHandler is called, the value of messageHandler is passed out to my test? Or do I need to redesign this? Are there any design patterns I should be using in this case? Does anyone know of any good resources on this kind of design?

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• How to avoid game rendering component circular references?

  - by CodexArcanum

  I'm working on a simple game design, and I wanted to break up my game objects into more reusable components. But I'm getting stuck on how exactly to implement the design I have in mind. Here's an example: I have a Logger object, whose job is simply to store a list of messages and render them to screen. You know, logging. Originally the Logger just held the list, and the game loop rendered it's contents. Then I moved the rendering logic into the Logger.Draw() method, and now I want to move it further into a LoggerRenderer object. In effect, I want to have the game loop call RenderAll, which will then call Logger.Render, which will in turn call the LoggerRenderer.Render and finally output the text. So the Logger needs to contain a Renderer object, but the Renderer needs access to the Logger's state (the message queue) in order to render. How do I resolve that? Should I be passing in the message queue and other state information explicitly to the Render method? Or should the game loop be calling the Renderer directly and it links back to the logger, but the RenderAll method never actually sees the logger object itself? This feels kind of like Command pattern, but I'm botching it up terribly.

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• Modeling related objects and their templates

  - by Duddle

  Hello everybody! I am having trouble correctly modeling related objects that can use templates. This is not homework, but part of a small project in the university. In this application the user can add several elements, which can either be passive or active. Each concrete element has different attributes, these must be set by the user. See diagram 1: Since the user will create many elements, we want there to be templates for each type of element, so some of the attributes are filled in automatically. See diagram 2: In my opinion, this is a bad design. For example, to get all possible templates for a PassiveElementA-object, there has to be a list/set somewhere that only holds PassiveElementATemplate-objects. There has to be a separate list for each subclass of Element. So if you wanted to add a new PassiveElement-child, you also have to edit the class which holds all these separate lists. I cannot figure out a good way to solve this problem. Since the concrete classes (i.e. PassiveElementA, ..., PassiveElementZ) have so many different attributes, many of the design patterns I know do not work. Thanks in advance for any hints, and sorry for my bad English.

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• What would you like to correct and/or improve in this java implementation of Chain Of Responsibility

  - by Maciek Kreft

  package design.pattern.behavioral; import design.pattern.behavioral.ChainOfResponsibility.*; public class ChainOfResponsibility { public static class Chain { private Request[] requests = null; private Handler[] handlers = null; public Chain(Handler[] handlers, Request[] requests){ this.handlers = handlers; this.requests = requests; } public void start() { for(Request r : requests) for (Handler h : handlers) if(h.handle(r)) break; } } public static class Request { private int value; public Request setValue(int value){ this.value = value; return this; } public int getValue() { return value; } } public static class Handler<T1> { private Lambda<T1> lambda = null; private Lambda<T1> command = null; public Handler(Lambda<T1> condition, Lambda<T1> command) { this.lambda = condition; this.command = command; } public boolean handle(T1 request) { if (lambda.lambda(request)) command.lambda(request); return lambda.lambda(request); } } public static abstract class Lambda<T1>{ public abstract Boolean lambda(T1 request); } } class TestChainOfResponsibility { public static void main(String[] args) { new TestChainOfResponsibility().test(); } private void test() { new Chain(new Handler[]{ // chain of responsibility new Handler<Request>( new Lambda<Request>(){ // command public Boolean lambda(Request condition) { return condition.getValue() >= 600; } }, new Lambda<Request>(){ public Boolean lambda(Request command) { System.out.println("You are rich: " + command.getValue() + " (id: " + command.hashCode() + ")"); return true; } } ), new Handler<Request>( new Lambda<Request>(){ public Boolean lambda(Request condition) { return condition.getValue() >= 100; } }, new Lambda<Request>(){ public Boolean lambda(Request command) { System.out.println("You are poor: " + command.getValue() + " (id: " + command.hashCode() + ")"); return true; } } ), }, new Request[]{ new Request().setValue(600), // chaining method new Request().setValue(100), } ).start(); } }

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• Maintain List of Active Users for Web

  - by Bryan Marble

  Problem Statement - Would like to know if particular web app user is active (i.e. logged in and using site) and be able to query for list of active users or determine a user's activity status. Constraints - Doesn't need to be exact (i.e. if a user was active within a certain timeframe, that's ok to say that they're active even if they've closed their browser). I feel like there should be a design pattern for this type of problem but haven't been able to find anything here or elsewhere on the web. Approaches I'm considering: Maintain a table that is updated any time a user performs an action (or some subset of actions). Would then query for users that have performed an action within some threshold of time. Try to monitor session information and maintain a table that lists logged in users and times out after a certain period of time. Some other more standard way of doing this? How would you approach this problem (again, from a design pattern perspective)? Thanks!

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• desing 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. country (ddl), state (ddl), city (ddl), boro (ddl), address (txtBox), zipcode(txtbox). and an object that represents a datarow with a value for each. 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 ddls. 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 possible values of country, then assign values, then load values of state, then assign value ans so on. 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. thanks

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• What do I name this class whose sole purpose is to report failure?

  - by Blair Holloway

  In our system, we have a number of classes whose construction must happen asynchronously. We wrap the construction process in another class that derives from an IConstructor class: class IConstructor { public: virtual void Update() = 0; virtual Status GetStatus() = 0; virtual int GetLastError() = 0; }; There's an issue with the design of the current system - the functions that create the IConstructor-derived classes are often doing additional work which can also fail. At that point, instead of getting a constructor which can be queried for an error, a NULL pointer is returned. Restructuring the code to avoid this is possible, but time-consuming. In the meantime, I decided to create a constructor class which we create and return in case of error, instead of a NULL pointer: class FailedConstructor : public IConstructor public: virtual void Update() {} virtual Status GetStatus() { return STATUS_ERROR; } virtual int GetLastError() { return m_errorCode; } private: int m_errorCode; }; All of the above this the setup for a mundane question: what do I name the FailedConstructor class? In our current system, FailedConstructor would indicate "a class which constructs an instance of Failed", not "a class which represents a failed attempt to construct another class". I feel like it should be named for one of the design patterns, like Proxy or Adapter, but I'm not sure which.

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• C++ interpreter conceptual problem

  - by Jan Wilkins

  I've built an interpreter in C++ for a language created by me. One main problem in the design was that I had two different types in the language: number and string. So I have to pass around a struct like: class myInterpreterValue { myInterpreterType type; int intValue; string strValue; } Objects of this class are passed around million times a second during e.g.: a countdown loop in my language. Profiling pointed out: 85% of the performance is eaten by the allocation function of the string template. This is pretty clear to me: My interpreter has bad design and doesn't use pointers enough. Yet, I don't have an option: I can't use pointers in most cases as I just have to make copies. How to do something against this? Is a class like this a better idea? vector<string> strTable; vector<int> intTable; class myInterpreterValue { myInterpreterType type; int locationInTable; } So the class only knows what type it represents and the position in the table This however again has disadvantages: I'd have to add temporary values to the string/int vector table and then remove them again, this would eat a lot of performance again. Help, how do interpreters of languages like Python or Ruby do that? They somehow need a struct that represents a value in the language like something that can either be int or string.

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