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  • MVP pattern. Presenter requires new view instance. Best practice

    - by Andrew Florko
    I try to apply MVP pattern for win.forms application. I have 2 forms: main & child. Main has a button and when you click it - child form should appear. There are 2 views interfaces that forms implement IMainView { event OnClick; ... } IChildView { ... } There are two presenters MainPresenter(IMainView) & ChildPresenter(IChildView) MainPresenter listens to OnClick event and then should create IChildView implementation. MainPresenter { ... MainClicked() { // it's required to create IChildView instance here } } How would you implement such creation typically? Shall IMainView has factory method for IChildView or may be it should be separate Views factory. What would you advise? Or maybe there is some misunderstanding of MVP here? Thank you in advance!

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  • which version of the code below is right?

    - by TheVillageIdiot
    Hi I found this function in a utilities code file: Version 1: public static bool IsValidLong(string strLong) { bool result = true; try { long tmp = long.Parse(strLong); } catch (Exception ex) { result = false; } return result; } I want to replace this (and validators for other types) with following: Version 2: public static bool IsValidLong(string strLong) { long l; return long.TryParse(strLong, out l); } which version is better and why?

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  • Decimal rounding strategies in enterprise applications

    - by Sapphire
    Well, I am wondering about a thing with rounding decimals, and storing them in DB. Problem is like this: Let's say we have a customer and a invoice. The invoice has total price of $100.495 (due to some discount percentage which is not integer number), but it is shown as $100.50 (when rounded, just for print on invoice). It is stored in the DB with the price of $100.495, which means that when customer makes a deposit of $100.50 it will have $0.005 extra on the account. If this is rounded, it will appear as $0, but after couple of invoices it would keep accumulating, which would appear wrong (although it actually is not). What is best to do in this case. Store the value of $100.50, or leave everything as-is?

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  • Haskel dot (.) and dollar ($) composition: correct use.

    - by Robert Massaioli
    I have been reading Real World Haskell and I am nearing the end but a matter of style has been niggling at me to do with the (.) and ($) operators. When you write a function that is a composition of other functions you write it like: f = g . h But when you apply something to the end of those functions I write it like this: k = a $ b $ c $ value But the book would write it like this: k = a . b . c $ value Now to me they look functionally equivalent, they do the exact same thing in my eyes. However, the more I look, the more I see people writing their functions in the manner that the book does: compose with (.) first and then only at the end use ($) to append a value to evaluate the lot (nobody does it with many dollar compositions). Is there a reason for using the books way that is much better than using all ($) symbols? Or is there some best practice here that I am not getting? Or is it superfluous and I shouldn't be worrying about it at all? Thanks.

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  • My first Lisp macro; is it leaky?

    - by Tom Martin
    I've been working through Practical Common Lisp and as an exercise decided to write a macro to determine if a number is a multiple of another number: (defmacro multp (value factor) `(= (rem ,value ,factor) 0)) so that : (multp 40 10) evaluates to true whilst (multp 40 13) does not The question is does this macro leak in some way? Also is this "good" Lisp? Is there already an existing function/macro that I could have used?

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  • Should HTTP POST be discouraged?

    - by Tomas Sedovic
    Quoting from the CouchDB documentation: It is recommended that you avoid POST when possible, because proxies and other network intermediaries will occasionally resend POST requests, which can result in duplicate document creation. To my understanding, this should not be happening on the protocol level (a confused user armed with a doubleclick is a completely different story). What is the best course of action, then? Should we really try to avoid POST requests and replace them by PUT? I don't like that as they convey a different meaning. Should we anticipate this and protect the requests by unique IDs where we want to avoid accidental duplication? I don't like that either: it complicates the code and prevents situations where multiple identical posts may be desired.

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  • Parallel Dev: Should developers work within the same branch?

    - by Zombies
    Should multiple developers work within the same branch, and update - modify - commit ? Or should each developer have his/her own each branch exclusively? And how would sharing branches impact an environment where you are doing routine maintenance as opposed to unmaintained code streams? Also, how would this work if you deploy each developers work as soon as it is done and passes testing (rapidly, as opposed to putting all of their work into a single release).

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  • Should old/legacy/unused code be deleted from source control repository?

    - by Checkers
    I've encountered this in multiple projects. As the code base evolves, some libraries, applications, and components get abandoned and/or deprecated. Most people prefer to keep them in. The usual argument is that the code does not really take any space, it can be left alone until needed again. So a repository slowly turns into a cesspool of legacy code, where it's hard to find anything. Some people delete old code, since it creates clutter, raises more questions for new people, and you can restore any old snapshot of the code base anyway. However you can't always find the old code if you don't know where to look, as none of the (common) VCS I know offer search over the entire repository including all historical revisions, and the only way to search the old files is to check out the revision where the deleted file exists. What would be a good approach to repository management?

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  • Generic Abstract Singleton with Custom Constructor in C#

    - by Heka
    I want to write a generic singleton with an external constructor. In other words the constructor can be modified. I have 2 designs in my mind but I don't know whether they are practical or not. First one is to enforce derived class' constructor to be non-public but I do not know if there is a way of it? Second one is to use a delegate and call it inside the constructor? It isn't necessarily to be a constructor. The reason I chose custom constructor is doing some custom initializations. Any suggestions would be appreciated :)

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  • tutorials/books to create a plugin/module/library?

    - by fayer
    i wonder if there are tutorials/books explaining how you create a library/plugin/module for other to implement? libraries/frameworks like solr, doctrine, codeigniter etc. cause it seems that they follow the same pattern. having one "bootstrap" file to load configurations, other classes and so on. i aim to understand the basics, so i can create a such library. cause at the moment i want to code an address book that other can use. just include a bootstrap file and they are ready to use my classes (like Doctrine). recommendations of sources to learn these things of stuff? you experienced guys, how did you learn it? thanks.

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  • Using typedefs (or #defines) on built in types - any sensible reason?

    - by jb
    Well I'm doing some Java - C integration, and throught C library werid type mappings are used (theres more of them;)): #define CHAR char /* 8 bit signed int */ #define SHORT short /* 16 bit signed int */ #define INT int /* "natural" length signed int */ #define LONG long /* 32 bit signed int */ typedef unsigned char BYTE; /* 8 bit unsigned int */ typedef unsigned char UCHAR; /* 8 bit unsigned int */ typedef unsigned short USHORT; /* 16 bit unsigned int */ typedef unsigned int UINT; /* "natural" length unsigned int*/ Is there any legitimate reason not to use them? It's not like char is going to be redefined anytime soon. I can think of: Writing platform/compiler portable code (size of type is underspecified in C/C++) Saving space and time on embedded systems - if you loop over array shorter than 255 on 8bit microprocessor writing: for(uint8_t ii = 0; ii < len; ii++) will give meaureable speedup.

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  • Use multiple css files or a single file organised by comments

    - by David
    Hi, what is regarded as the best approach to organising css. At the moment I am using a single link in the head of my xhtml documents as follows: <link rel="stylesheet" type="text/css" href="style/imports.css" /> In this file im importing several different css files i.e. reset.css, structure.css, skin.css I know there is an overhead in doing this as each requires an extra trip to the server but it makes things much more logical and organised in my opinion. Does anyone have an opinion on how best to organise their css. - Would it be better to put all these seperate css funcions into one single file? Also, is it best practice to minify css.

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  • How do I correct feature envy in this case?

    - by RMorrisey
    I have some code that looks like: class Parent { private Intermediate intermediateContainer; public Intermediate getIntermediate(); } class Intermediate { private Child child; public Child getChild() {...} public void intermediateOp(); } class Child { public void something(); public void somethingElse(); } class Client { private Parent parent; public void something() { parent.getIntermediate().getChild().something(); } public void somethingElse() { parent.getIntermediate().getChild().somethingElse(); } public void intermediate() { parent.getIntermediate().intermediateOp(); } } I understand that is an example of the "feature envy" code smell. The question is, what's the best way to fix it? My first instinct is to put the three methods on parent: parent.something(); parent.somethingElse(); parent.intermediateOp(); ...but I feel like this duplicates code, and clutters the API of the Parent class (which is already rather busy). Do I want to store the result of getIntermediate(), and/or getChild(), and keep my own references to these objects?

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  • How to solve the "Growing If Statement" problem?

    - by Achilles
    I've been doing some reading about design patterns and wanted some perspective. Consider the following: Dim objGruntWorker as IGruntWorker if SomeCriteria then objGruntWorker = new GoFor() else if SomeOtherCriteria then objGruntWorker = new Newb() else if SomeCriteriaAndTheKitchenSink then objGruntWorker = new CubeRat() end if objGruntWorker.GetBreakfast() system.threading.thread.sleep(GetMilliSecondsFromHours(4)) objGruntWorker.GetLunch() The above code grows each time a new Criteria arises. I've seen code like this all over the place and in ignorance wrote some of it myself. How should this be solved? Does this kind of anti-pattern have a more "formal" name? Thanks for your help!

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  • Wait For Return Key Press Using Java Scanner

    - by Gordon
    What would be the best way to wait for a return key press from the user using the Java Scanner Class? In a command line tool I would like the user to confirm before carrying out an action. Please correct me if there a more standard way of doing this in a command line tool.

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  • Learning Javascript in one weekend?

    - by dueyfinster
    Similiar to this question, I am wondering if experienced Javascript developers have any websites they use with examples to get the basics of Javascript down in 24/28 hours? I have looked at Douglas Crockford's Google Tech Talk and I bought the book "Javascript: the good parts" but I haven't had time to read it.

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  • ASP.NET MVC Filters: How to set Viewdata for Dropdown based on action paramter

    - by CRice
    Hi, Im loading an entity 'Member' from its id in route data. [ListItemsForMembershipType(true)] public ActionResult Edit(Member someMember) {...} The attribute on the action loads the membership type list items for a dropdown box and sticks it in viewdata. This is fine for add forms, and search forms (it gets all active items) but I need the attribute to execute BASED ON THE VALUE someMember.MembershipTypeId, because its current value must always be present when loading the item (i.e. all active items, plus the one from the loaded record). So the question is, what is the standard pattern for this? How can my attribute accept the value or should I be loading the viewdata for the drop down in a controller supertype or during model binding or something else? It is in an attribute now because the code to set the viewdata would otherwise be duplicated in each usage in each action.

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  • Preprocessor "macro function" vs. function pointer - best practice?

    - by Dustin
    I recently started a small personal project (RGB value to BGR value conversion program) in C, and I realised that a function that converts from RGB to BGR can not only perform the conversion but also the inversion. Obviously that means I don't really need two functions rgb2bgr and bgr2rgb. However, does it matter whether I use a function pointer instead of a macro? For example: int rgb2bgr (const int rgb); /* * Should I do this because it allows the compiler to issue * appropriate error messages using the proper function name, * not to mention possible debugging benefits? */ int (*bgr2rgb) (const int bgr) = rgb2bgr; /* * Or should I do this since it is merely a convenience * and they're really the same function anyway? */ #define bgr2rgb(bgr) (rgb2bgr (bgr)) I'm not necessarily looking for a change in execution efficiency as it's more of a subjective question out of curiosity. I am well aware of the fact that type safety is neither lost nor gained using either method. Would the function pointer merely be a convenience or are there more practical benefits to be gained of which I am unaware?

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  • Testing When Correctness is Poorly Defined?

    - by dsimcha
    I generally try to use unit tests for any code that has easily defined correct behavior given some reasonably small, well-defined set of inputs. This works quite well for catching bugs, and I do it all the time in my personal library of generic functions. However, a lot of the code I write is data mining code that basically looks for significant patterns in large datasets. Correct behavior in this case is often not well defined and depends on a lot of different inputs in ways that are not easy for a human to predict (i.e. the math can't reasonably be done by hand, which is why I'm using a computer to solve the problem in the first place). These inputs can be very complex, to the point where coming up with a reasonable test case is near impossible. Identifying the edge cases that are worth testing is extremely difficult. Sometimes the algorithm isn't even deterministic. Usually, I do the best I can by using asserts for sanity checks and creating a small toy test case with a known pattern and informally seeing if the answer at least "looks reasonable", without it necessarily being objectively correct. Is there any better way to test these kinds of cases?

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  • Saving a Django form with a Many2Many field with through table

    - by PhilGo20
    So I have this model with multiple Many2Many relationship. 2 of those (EventCategorizing and EventLocation are through tables/intermediary models) class Event(models.Model): """ Event information for Way-finding and Navigator application""" categories = models.ManyToManyField('EventCategorizing', null=True, blank=True, help_text="categories associated with the location") #categories associated with the location images = models.ManyToManyField(KMSImageP, null=True, blank=True) #images related to the event creator = models.ForeignKey(User, verbose_name=_('creator'), related_name="%(class)s_created") locations = models.ManyToManyField('EventLocation', null=True, blank=True) In my view, I first need to save the creator as the request user, so I use the commit=False parameter to get the form values. if event_form.is_valid(): event = event_form.save(commit=False) #we save the request user as the creator event.creator = request.user event.save() event = event_form.save_m2m() event.save() I get the following error: *** TypeError: 'EventCategorizing' instance expected I can manually add the M2M relationship to my "event" instance, but I am sure there is a simpler way. Am I missing on something ?

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  • WPF binding to a boolean on a control

    - by Jose
    I'm wondering if someone has a simple succinct solution to binding to a dependency property that needs to be the converse of the property. Here's an example I have a textbox that is disabled based on a property in the datacontext e.g.: <TextBox IsEnabled={Binding CanEdit} Text={Binding MyText}/> The requirement changes and I want to make it ReadOnly instead of disabled, so without changing my ViewModel I could do this: In the UserControl resources: <UserControl.Resources> <m:NotConverter x:Key="NotConverter"/> </UserControl.Resources> And then change the TextBox to: <TextBox IsReadOnly={Binding CanEdit,Converter={StaticResource NotConverter}} Text={Binding MyText}/> Which I personally think is EXTREMELY verbose I would love to be able to just do this(notice the !): <TextBox IsReadOnly={Binding !CanEdit} Text={Binding MyText}/> But alas, that is not an option that I know of. I can think of two options. Create an attached property IsNotReadOnly to FrameworkElement(?) and bind to that property If I change my ViewModel then I could add a property CanEdit and another CannotEdit which I would be kind of embarrassed of because I believe it adds an irrelevant property to a class, which I don't think is a good practice. The main reason for the question is that in my project the above isn't just for one control, so trying to keep my project as DRY as possible and readable I am throwing this out to anyone feeling my pain and has come up with a solution :)

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