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  • Distinguishing between UI command & domain commands

    - by SonOfPirate
    I am building a WPF client application using the MVVM pattern that provides an interface on top of an existing set of business logic residing in a library which is shared with other applications. The business library followed a domain-driven architecture using CQRS to separate the read and write models (no event sourcing). The combination of technologies and patterns has brought up an interesting conundrum: The MVVM pattern uses the command pattern for handling user-interaction with the view models. .NET provides an ICommand interface which is implemented by most MVVM frameworks, like MVVM Light's RelayCommand and Prism's DelegateCommand. For example, the view model would expose a number of command objects as properties that are bound to the UI and respond when the user performs actions like clicking buttons. Many implementations of the CQRS use the command pattern to isolate and encapsulate individual behaviors. In my business library, we have implemented the write model as command / command-handler pairs. As such, when we want to do some work, such as create a new order, we 'issue' a command (CreateOrderCommand) which is routed to the command-handler responsible for executing the command. This is great, clearly explained in many sources and I am good with it. However, take this scenario: I have a ToolbarViewModel which exposes a CreateNewOrderCommand property. This ICommand object is bound to a button in the UI. When clicked, the UI command creates and issues a new CreateOrderCommand object to the domain which is handled by the CreateOrderCommandHandler. This is difficult to explain to other developers and I am finding myself getting tongue-tied because everything is a command. I'm sure I'm not the first developer to have patterns overlap like this where the naming/terminology also overlap. How have you approached distinguishing your commands used in the UI from those used in the domain? (Edit: I should mention that the business library is UI-agnostic, i.e. no UI technology-specific code exists, or will exists, in this library.)

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  • Go/Obj-C style interfaces with ability to extend compiled objects after initial release

    - by Skrylar
    I have a conceptual model for an object system which involves combining Go/Obj-C interfaces/protocols with being able to add virtual methods from any unit, not just the one which defines a class. The idea of this is to allow Ruby-ish open classes so you can take a minimalist approach to library development, and attach on small pieces of functionality as is actually needed by the whole program. Implementation of this involves a table of methods marked virtual in an RTTI table, which system functions are allowed to add to during module initialization. Upon typecasting an object to an interface, a Go-style lookup is done to create a vtable for that particular mapping and pass it off so you can have comparable performance to C/C++. In this case, methods may be added /afterwards/ which were not previously known and these new methods allow newer interfaces to be satisfied; while I like this idea because it seems like it would be very flexible (disregarding the potential for spaghetti code, which can happen with just about any model you use regardless). By wrapping the system calls for binding methods up in a set of clean C-compatible calls, one would also be able to integrate code with shared libraries and retain a decent amount of performance (Go does not do shared linking, and Objective-C does a dynamic lookup on each call.) Is there a valid use-case for this model that would make it worth the extra background plumbing? As much as this Dylan-style extensibility would be nice to have access to, I can't quite bring myself to a use case that would justify the overhead other than "it could make some kinds of code more extensible in future scenarios."

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  • Versioning APIs

    - by Sharon
    Suppose that you have a large project supported by an API base. The project also ships a public API that end(ish) users can use. Sometimes you need to make changes to the API base that supports your project. For example, you need to add a feature that needs an API change, a new method, or requires altering of one of the objects, or the format of one of those objects, passed to or from the API. Assuming that you are also using these objects in your public API, the public objects will also change any time you do this, which is undesirable as your clients may rely on the API objects remaining identical for their parsing code to work. (cough C++ WSDL clients...) So one potential solution is to version the API. But when we say "version" the API, it sounds like this also must mean to version the API objects as well as well as providing duplicate method calls for each changed method signature. So I would then have a plain old clr object for each version of my api, which again seems undesirable. And even if I do this, I surely won't be building each object from scratch as that would end up with vast amounts of duplicated code. Rather, the API is likely to extend the private objects we are using for our base API, but then we run into the same problem because added properties would also be available in the public API when they are not supposed to be. So what is some sanity that is usually applied to this situation? I know many public services such as Git for Windows maintains a versioned API, but I'm having trouble imagining an architecture that supports this without vast amounts of duplicate code covering the various versioned methods and input/output objects. I'm aware that processes such as semantic versioning attempt to put some sanity on when public API breaks should occur. The problem is more that it seems like many or most changes require breaking the public API if the objects aren't more separated, but I don't see a good way to do that without duplicating code.

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  • Triggering Data Changes in N-Tier

    - by Ryan Kinal
    I've been studying n-tier architectures as of late, particularly in VB.NET with Entity Framework and/or LINQ to SQL. I understand the basic concepts, but have been wondering about best practices in regard to triggering CRUD-type operations from user input/action. So, the arcitecture looks something like the following: [presentation layer] - [business layer] - [data layer] - (database) Getting information from the database into the presentation layer is simple and abstracted. It's just a matter of instantiating a new object from the business layer, which in turn uses the data layer to get at the correct information. However, saving (updating and inserting), and deleting seem to require particular APIs on the relevant business objects. I have to assume this is standard practice, unless a business object will save itself on various operations (which seems inefficient), or on disposal (which seems like it just wouldn't work, or may be unwieldy and unreliable). Should my "savable" business objects all implement a particular "ISavable" or "IDatabaseObject" interface? Is this a recognized (anti-)pattern? Are there other, better patterns I should be using that I'm just unaware of? The TLDR question, I suppose, is How does the presentation layer trigger database changes?

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  • Player & Level class structure in 2D python console game?

    - by Markus Meskanen
    I'm trying to create a 2D console game, where I have a player who can freely move around in a level (~map, but map is a reserved keyword) and interfere with other objects. Levels construct out of multiple Blocks, such as player(s), rocks, etc. Here's the Block class: class Block(object): def __init__(self, x=0, y=0, char=' ', solid=False): self.x = x self.y = y self.char = char self.solid = solid As you see, each block has a position (x, y) and a character to represent the block when it's printed. Each block also has a solid attribute, defining whether it can overlap with other solids or not. (Two solid blocks cannot overlap) I've now created few subclasses from Block (Rock might be useless for now) class Rock(Block): def __init__(self, x=0, y=0): super(Rock, self).__init__(x, y, 'x', True) class Player(Block): def __init__(self, x=0, y=0): super(Player, self).__init__(x, y, 'i', True) def move_left(self, x=1): ... # How do I make sure Player wont overlap with rocks? self.x -= x And here's the Level class: class Level(object): def __init__(self, name='', blocks=None): self.name = name self.blocks = blocks or [] Only way I can think of is to store a Player instance into Level's attributes (self.player=Player(), or so) and then give Level a method: def player_move_left(self): for block in self.blocks: if block.x == self.player.x - 1 and block.solid: return False But this doesn't really make any sense, why have a Player class if it can't even be moved without Level? Imo. player should be moved by a method inside Player. Am I wrong at something here, if not, how could I implement such behavior?

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  • What patterns book for iOS development contains this specific information? [closed]

    - by Brett Ryan
    I've read several books on iOS development and Objective-C, however what a lot of them teach is how to work with interfaces and all contain the model inside the view controller, i.e. a UITableViewController based view will simply have an NSArray as it's model. I'm interested in what the best practices are for designing the structure of an application. Specifically I'm interested in best practices for the following: How to separate a model from the view controller. I think I know how to do this by simply replacing the NSArray style example with a specific model object, however what I do not know how to do is alert the view when the model changes. For example in .NET I would solve this by conforming to INotifyPropertyChanged and databinding, and similarly with Java I would use PropertyChangeListener. How to create a service model for my domain objects. For example I want to learn the best way to create a service for a hypothetical Widget object to manage an internal DB and also services for communicating with remote endpoints. I need to learn the best ways to do this in a way that interface components can subscribe to events such as widgetUpdated. These services should be singleton classes and some how dependency injected into model/controller objects. Books I've read so far are: Programming in Objective-C (4th Edition) Beginning iOS 5 Development: Exploring the iOS SDK The iOS 5 Developer's Cookbook: Expanded Electronic Edition: Essentials and Advanced Recipes for iOS Programmers Learn Objective-C on the Mac: For OS X and iOS I've also purchased the following updated books but not yet read them. The Core iOS 6 Developer's Cookbook (4th edition Programming in Objective-C (5th Edition) I come from a Java and C# background with 15 years experience, I understand that many of the ways I would do things in these languages may not fit to the ObjC way of developing applications. Would someone be able to provide me with the book on this topic containing this specific subject matter?

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  • Making a class pseudo-immutable by setting a flag

    - by scott_fakename
    I have a java project that involves building some pretty complex objects. There are quite a lot (dozens) of different ones and some of them have a HUGE number of parameters. They also need to be immutable. So I was thinking the builder pattern would work, but it ends up require a lot of boilerplate. Another potential solution I thought of was to make a mutable class, but give it a "frozen" flag, a-la ruby. Here is a simple example: public class EqualRule extends Rule { private boolean frozen; private int target; public EqualRule() { frozen = false; } public void setTarget(int i) { if (frozen) throw new IllegalStateException( "Can't change frozen rule."); target = i; } public int getTarget() { return target; } public void freeze() { frozen = true; } @Override public boolean checkRule(int i) { return (target == i); } } and "Rule" is just an abstract class that has an abstract "checkRule" method. This cuts way down on the number of objects I need to write, while also giving me an object that becomes immutable for all intents and purposes. This kind of act like the object was its own Builder... But not quite. I'm not too excited, however, about having an immutable being disguised as a bean however. So I had two questions: 1. Before I go too far down this path, are there any huge problems that anyone sees right off the bat? For what it's worth, it is planned that this behavior will be well documented... 2. If so, is there a better solution? Thanks

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  • Is there a better way to organize my module tests that avoids an explosion of new source files?

    - by luser droog
    I've got a neat (so I thought) way of having each of my modules produce a unit-test executable if compiled with the -DTESTMODULE flag. This flag guards a main() function that can access all static data and functions in the module, without #including a C file. From the README: -- Modules -- The various modules were written and tested separately before being coupled together to achieve the necessary basic functionality. Each module retains its unit-test, its main() function, guarded by #ifdef TESTMODULE. `make test` will compile and execute all the unit tests, producing copious output, but importantly exitting with an appropriate success or failure code, so the `make test` command will fail if any of the tests fail. Module TOC __________ test obj src header structures CONSTANTS ---- --- --- --- -------------------- m m.o m.c m.h mfile mtab TABSZ s s.o s.c s.h stack STACKSEGSZ v v.o v.c v.h saverec_ f.o f.c f.h file ob ob.o ob.c ob.h object ar ar.o ar.c ar.h array st st.o st.c st.h string di di.o di.c di.h dichead dictionary nm nm.o nm.c nm.h name gc gc.o gc.c gc.h garbage collector itp itp.c itp.h context osunix.o osunix.c osunix.h unix-dependent functions It's compile by a tricky bit of makefile, m:m.c ob.h ob.o err.o $(CORE) itp.o $(OP) cc $(CFLAGS) -DTESTMODULE $(LDLIBS) -o $@ $< err.o ob.o s.o ar.o st.o v.o di.o gc.o nm.o itp.o $(OP) f.o where the module is compiled with its own C file plus every other object file except itself. But it's creating difficulties for the kindly programmer who offered to write the Autotools files for me. So the obvious way to make it "less weird" would be to bust-out all the main functions into separate source files. But, but ... Do I gotta?

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  • Algorithm design, "randomising" timetable schedule in Python although open to other languages.

    - by S1syphus
    Before I start I should add I am a musician and not a native programmer, this was undertook to make my life easier. Here is the situation, at work I'm given a new csv file each which contains a list of sound files, their length, and the minimum total amount of time they must be played. I create a playlist of exactly 60 minutes, from this excel file. Each sample played the by the minimum number of instances, but spread out from each other; so there will never be a period where for where one sound is played twice in a row or in close proximity to itself. Secondly, if the minimum instances of each song has been used, and there is still time with in the 60 min, it needs to fill the remaining time using sounds till 60 minutes is reached, while adhering to above. The smallest duration possible is 15 seconds, and then multiples of 15 seconds. Here is what I came up with in python and the problems I'm having with it, and as one user said its buggy due to the random library used in it. So I'm guessing a total rethink is on the table, here is where I need your help. Whats is the best way to solve the issue, I have had a brief look at things like knapsack and bin packing algorithms, while both are relevant neither are appropriate and maybe a bit beyond me.

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  • How to design a command line program and keep it open for a future GUI?

    - by systempuntoout
    What are some best practices to keep in mind when developing a script program that could be integrated with a GUI, probably by somebody else, in the future? Example scenario: i develop a fancy python CLI program that scrapes every unicorn images from the web i decide to publish it on github a unicorn fan programmer decide to take the sources and build a GUI on them. he gives up because my code is a mess How do i avoid step 4 and let unicorn fan programmer build his GUI without hassle?

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

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

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  • Looking for design/architecture suggestions for a simple HTML game.

    - by z-boss
    Imagine that HTML page is a game surface (see picture). User can have n number of boards (blue divs) on his page. Each board can be moved, re-sized, relabeled, created new and removed. Inside each board there are m number of figures (purple divs). Each of these user can move inside the board or to another board, re-size, change color and label, delete, add new. The goal of the game is not important, but let's say it is to rearrange figures in a certain way so that they disappear. But the goal of the programmer is to save the whole game surface in the database for every user of the site, and to load it later when he returns. So, how do I go about data exchange between client and the database? I'll give my idea in one of the answers.

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  • Looking for help with a design for a simple C# calendar app.

    - by Vladislav
    As a personal project, I'm putting together a C# WPF calendar. I'm stuck on coding the calendar screen - specifically, the 5x7 grid of days. I've first tried to code it using elements like Panels, Labels, and Buttons. I've decided that was too cumbersome. I've then decided to use GDI to draw the calendar myself. I now have a wonderful layout - but I'm not sure how to handle interactive regions of the calendar. (Say, Previous/Next month, clicking on any particular day...) After rendering the calendar screen, should I be creating button objects for all those tasks, and assigning onClick handlers to them? Or is there an alternative solution? Thanks in advance. -Vladislav

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  • GUI Design - Roleselection with two lists, selected roles on the right, or left list?

    - by subes
    Hi, image two lists for selecting roles for a new user creation in an administrator frontend. One list has all available roles in it and another has the selected roles in it. Between those lists are buttons to move elements from one list to another. Thus the layout is horizontal with [List] [Buttons] [List]. Now to the question: Should the selected elements be on the left, or the right list? Intuitively some people I asked say, that the selected elements have to be on the right list. But some other people follow some sort of guideline that says, that the more important stuff in a frontend has to be on the left side. Also they think the selected elements are more important than the non-selected and so the selected ones have to be on the left side. Whats your opinion?

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  • How to best integrate HTML/design with C# code in ASP.Net or ASP.Net MVC?

    - by LuftMensch
    We're working on a new ASP.Net site. The last major site we did was in classic ASP--the procedure we used there was to have the HTML completed first, then "bring it to life" with the ASP code. In the ASP.Net world, how does this work? I.e. how do the designers do their work if much of the mark-up is actually being generated by the server controls? We are also looking at ASP.Net MVC as a potential lightweight alternative. Would be very interested to know what was worked best for people in both scenarios in terms of working with the designers and integrating their work with the code.

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  • Develop an classic UI or be bold with a newer design?

    - by DeanMc
    Forgive me if this is the wrong place but I am curious as to how other programmers feel about this topic: I am currently working on my portfolio site, it is being designed and built in silverlight 4. I initially started off with a typical stylised e-folio theme much like a standard website in terms of layout and flow. As I work more in the concept stages something has struck me. Am I trying to shoe-horn yesterday into today? What I am talking about is UI expectations. I'm all for clean user interfaces but that does not mean they should not take advantage of new concepts in presentation right? If you where to develop a site in silverlight as your own portfolio piece would you stick to the tried and tested "website" feel or would you try to come up with a UI that is intuitive and complements the technology? I feel that UI discussions are all the more important now that all forms of web development are allowing better methods to engage the user.

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  • Design pattern for Fat Client - Thin Client to use Common code?

    - by kurozakura
    Windows-based client application and web-client application(consuming the same code which windows-client uses) what is the preferable pattern for this scenario? Is it ok to have the code in the common place where both the projects and refer it as dll i.e one which is a windows app and other which is going consume the same code which windows client will be exposing.

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  • Which are the most important media queries to use in creating mobile responsive design?

    - by Matt
    There are a lot different media queries for mobile screen sizes. It can be overwhelming to accomodate all of them when designing a responsive mobile site. Which are the most important ones to use when designing for mobile? I found this article that does a pretty good job of outlining the available media queries: http://css-tricks.com/snippets/css/media-queries-for-standard-devices/. /* Smartphones (portrait and landscape) ----------- */ @media only screen and (min-device-width : 320px) and (max-device-width : 480px) { /* Styles */ } /* Smartphones (landscape) ----------- */ @media only screen and (min-width : 321px) { /* Styles */ } /* Smartphones (portrait) ----------- */ @media only screen and (max-width : 320px) { /* Styles */ } /* iPads (portrait and landscape) ----------- */ @media only screen and (min-device-width : 768px) and (max-device-width : 1024px) { /* Styles */ } /* iPads (landscape) ----------- */ @media only screen and (min-device-width : 768px) and (max-device-width : 1024px) and (orientation : landscape) { /* Styles */ } /* iPads (portrait) ----------- */ @media only screen and (min-device-width : 768px) and (max-device-width : 1024px) and (orientation : portrait) { /* Styles */ } /* Desktops and laptops ----------- */ @media only screen and (min-width : 1224px) { /* Styles */ } /* Large screens ----------- */ @media only screen and (min-width : 1824px) { /* Styles */ } /* iPhone 4 ----------- */ @media only screen and (-webkit-min-device-pixel-ratio : 1.5), only screen and (min-device-pixel-ratio : 1.5) { /* Styles */ }

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