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• How do I maintain coherency between model and view-model in MVVM pattern?

  - by Mike Garrett

  Problem Statement I'm writing a very basic WPF application to alter the contents of a configuration file. The data format is an XML file with a schema. I want to use it as a learning project for MVVM, so I have duly divided the code into Model: C# classes auto-generated from xsd.exe View-Model: View-friendly representation of the Model. View: Xaml and empty code behind I understand how the View-Model can make View-binding a breeze. However, doesn't that leave the View-Model <- Model semantics very awkward? Xsd.exe generates C# classes with arrays for multiple XML elements. However, at the V-VM level you need Observable Collections. Questions: Does this really mean I have to keep two completely different collection types representing the same data in coherence? What are the best practices for maintaining coherence between the Model and the View-Model?

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• elisp newbie question: Can't find 'filename' function definition in org.el?

  - by Dave Paroulek

  I really love org-mode in emacs and want to customize a few things. While reading thru org.el, I'm finding several references to filename but can't find filename using describe-function? I'm sure there's a simple answer, but I'm just learning elisp and it's not obvious. Any insight into where filename is defined? And/or if it's not a function, what is it? For example, filename on line 25502: (filename (if to-buffer (expand-file-name (concat (file-name-sans-extension (or (and subtree-p (org-entry-get (region-beginning) "EXPORT_FILE_NAME" t)) (file-name-nondirectory buffer-file-name))) "." html-extension) (file-name-as-directory (or pub-dir (org-export-directory :html opt-plist))))))

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• Please list here your deliberate practices in software development...

  - by JDelage

  What are your deliberate practices in relation with your work as a software developer / professional, or as a CS student? Deliberate practice are exercise and repetitions targeted specifically at an individual's weak points and meant to consistently stretch / grow someone's ability. It was described in this Anders Ericsson paper. To qualify as a deliberate practice, the exercise must satisfy the following: Is not inherently enjoyable. Is not play or paid practice. Is relevant to the skill being developed. Is not simply watching the skill being performed. Requires effort and attention from the learner. Often involves activities selected by a coach or teacher to facilitate learning. Please answer with one practice per answer. I'll seed the question with one possible answer.

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• How can I implement my own version of a MVC framework in ASP.NET?

  - by ace

  Hi - I would like to know how I can go about implementing my own version of a MVC framework in ASP.NET? I know there already is Microsoft provided ASP.NET MVC framework, but I want to learn MVC and thought the best way would be to implement my own flavor of a MVC framework on top of ASP.NET. Any thoughts / guidance ? Also, can anyone point me to a page where I can learn more about how microsoft implemented ASP.NET MVC ? I'm more interested in learning about the under the hood plumbing that goes on to implement the framework on top of asp.net, do they use HttpHandlers / HttpModules ? Thanks.

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• How to handle similar items in rails MVC?

  - by mocker

  I'm working on building a pretty simple site mainly as an exercise in learning more about rails. You can see my rough progress at statific.com. It's working pretty much as I wanted it for keeping track of server information, but now I'd like to expand it to other things, next on the list being firewalls. I can pretty easily duplicate all the models, views, etc.. that I have for my servers. The problem I see with that is that it isn't very DRY since most of the code would look the same, the only difference would be the attributes I have setup for firewalls would be different than for servers. I know in plain ruby this is pretty simple, you can have a 'Product' w/ common attributes ('manufacturer', 'model') and then have children with more specific attributes. Does the same type of concept exist for rails, or am I just over thinking this?

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• IronPython :- Visual Studio 2010 or SharpDevelop?

  - by Cruachan

  I'm considering developing a medium-size project for a client in IronPython. It's a pretty straightforward replacement for an existing system I've been supporting for several years, so the specification is quite well defined and understood. This is my first significant IronPython and .Net project so I'm expecting a bit of a learning curve. I was going to use SharpeDevelop, but I can purchase VisualStudion 2010 for a reasonable price and whilst I understood that IronPython Tools for Visual Studio 2008 were not so good, I haven't seen anything about the update for 2010 yet. Has anyone used either or both of these in a reasonable-sized commercial environment and do you have any recommendations? (and I'm aware of this question, but this is specifically about VS2010)

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• How do I maintain scroll position in MVC?

  - by Eric Brown

  Im working on a project in MVC and have enjoyed learning about it. There are a few growing pains but once you figure them out it's not bad. One thing that is really simple in the WebForms world is maintaining the scroll position on a page. All you do is set the MaintainScrollPositionOnPostback property to true. However, in MVC, Im not using postbacks so this will not work for me. What is the standard way of handling this? Edit: Ajax is acceptable, but I was also wondering how you would do it without AJAX.

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• Is using decimal ranges in a switch impossible in C#?

  - by phobia

  I'm justing starting out learning C# and I've become stuck at something very basic. For my first "app" I thought I'd go for something simple, so I decided for a BMI calculator. The BMI is calculated into a decimal type which I'm now trying to use in a switch statement, but aparently decimal can't be used in a switch? What would be the C# solution for this: decimal bmi = calculate_bmi(h, w); switch (bmi) { case < 18.5: bmi_description = "underweight."; break; case > 25: bmi_description = "overweight"; case > 30: bmi_description = "very overweight"; case > 40: bmi_description = "extreme overweight"; break; }

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• Php PEAR, Database Abstraction & Factory Methods

  - by pws5068

  I'm interested in learning more about design practices in PHP for Database Abstraction & Factory methods. For background, my site is a special-interest social networking community currently in beta mode. Currently, I've started moving my old code for object retrieval to factory methods. However, I do feel like I'm limiting myself by keeping a lot of SQL table names and structure separated in each function/method. Questions: 1.) Is there a reason to use PEAR (or similar) if I dont anticipate switching databases? 2.) Can PEAR interface with the MySqli prepared statements I currently use? 3.) Will it help me separate table names from each method? (If no, what other design patterns might I want to research?) 4.) Will it slow down my site once I have a significantly large member base?

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• BlueJ Chpt 4 - Auction Project - How to make removeLot method work after entering a new lot

  - by Ellaine Ryan

  Hi All I am learning Java through BlueJ I would like to add a removeLot method to the Auction Class in BlueJ Chpt 4. This involves also returning the lot with the given number or null if there is no such lot. If you enter , say 5 lots and then use the remove method, this codes removes whichever lot you specify. However if you enter a new lot after using the removeLot method - an internal error message comes up regarding lotnumbering . Any ideas? Thanks Elaine public Lot removeLot(int number) { if((number >= 1) ) { } Lot lot = getLot (number); if(lot !=null) { lots.remove(lot); } return lot; }

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• What fields have job security?

  - by computergeek6

  I can program pretty well, and I'm trying to think of a programming area that I can practice so I have a better chance of getting a job when I finish my education. I'm currently learning game development, but there are a ton of other people trying to get into game dev, so I want to find something a little more secure and sustainable to develop skills in. I've thought of things like financial systems and engineering stuff, but nothing I can think of is accessible to someone in high school. I'm trying to find something that involves physics or networking and isn't as popular a field as game dev. Does anyone have any ideas?

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• How to unit test internals (organization) of a data structure?

  - by Herms

  I've started working on a little ruby project that will have sample implementations of a number of different data structures and algorithms. Right now it's just for me to refresh on stuff I haven't done for a while, but I'm hoping to have it set up kind of like Ruby Koans, with a bunch of unit tests written for the data structures but the implementations empty (with full implementations in another branch). It could then be used as a nice learning tool or code kata. However, I'm having trouble coming up with a good way to write the tests. I can't just test the public behavior as that won't necessarily tell me about the implementation, and that's kind of important here. For example, the public interfaces of a normal BST and a Red-Black tree would be the same, but the RB Tree has very specific data organization requirements. How would I test that?

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• Problems with classes (super new)

  - by user260036

  Hi, I've problems to figure it out what's happening in the following exercise, I'm learning Smalltalk, so I'm newbie. Class Anew ^super new initialize. Ainitialize a:=0. Class Bnew: aParameter |instance| instance := super new. instance b: instance a + aParameter. ^instance Binitialize b:=0. The problem says what happen when the following code is executed: B new:10. But I can't not figure it out why instance variable does not belong to A class. Thanks

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• Initialize window code Mac OS X

  - by Jarle

  I'm currently reading "the red book" for learning OpenGL properly, and in one of the first examples, the author writes a line that says "InitializeAWindowPlease();" as a place holder for the code that will make a window to draw the OpenGL content in. Since I'm using Xcode for my programing, I know that I "get" a window to work with automatically (and that I have to make my own OpenGL view in interfacebuilder). How can I make this with pure code? I'm trying to learn programming, and I'm not to happy about taking "shortcuts" all the time. How can I make a window to draw my openGL stuff in? With Objective-C and C code I would love to see it. My goal is that I can make it without opening interface builder at all:)

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• Graph Databases' Implementation

  - by user1478153

  I am having trouble visualizing a Graph Database. Visualizing an RDBMS is really very simple and I was able to understand from the first tutorial itself when I started learning it some 4-5 years ago. But I am not able to understand Graph Databases. I am also unable to get any good links on this topic, hence posting this question here. Specifically, I am looking for the following: Some really simple book/link on Graph Dbs Atleast some knowledge on the implementation details of a Graph DB (I hope all Graph DBs would be having atleast a few basic things in common). Thanks a lot in advance guys,

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• simple python file writing question

  - by aharon

  I'm learning Python, and have run into a bit of a problem. On my OSX install of Python 3.1, this happens in the console: >>> filename = "test" >>> reader = open(filename, 'r') >>> writer = open(filename, 'w') >>> reader.read() '' >>> writer.write("hello world\n") 12 >>> reader.read() '' And calling more test in BASH confirms that there is nothing in test. What's going on? Thanks.

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• Shall i learn Assembly Language or C, to Understand how "real programming" works?

  - by Daniel Upton

  Hello, World.. I'm a web developer mostly working in Ruby and C#.. I wanna learn a low level language so i dont look like an ass infront of my (computer science expert) boss. Ive heard a lot of purist buzz about how assembly language is the only way to learn how computers actually work, but on the other hand C would probably be more useful as a language rather than just for theory. So my question is.. Would Learning C teach me enough computer science theory / low level programming to not look like a common dandy (complete tool)? Thanks! Daniel

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• How to use NSTableView's selectedRowIndexes?

  - by Jakub Lédl

  Hi guys, I'm just learning some basic programming in Objective C and Cocoa. I'm trying to get some data from NSTableView. Based on what I read in one tutorial, I wrote this: NSArray * items = [[itemsTableView selectedRowEnumerator] allObjects]; But then I learned that selectedRowEnumerator was deprecated already in 10.3 Panther and that I should use selectedRowIndexes. The problem is, I didn't find how to actually use the returned NSIndexSet to achieve the same result as with code written above. So, If anyone could give me a tip, I would be very grateful. Thanks.

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• Are there any purely functional Schemes or Lisps?

  - by nickname

  Over the past few months, I've put a lot of effort into learning (or attempting to learn) several functional programming languages. I really like math, so they have been very natural for me to use. Simply to be more specific, I have tried Common Lisp, Scheme, Haskell, OCaml, and (a little bit of) Erlang. I did not like the syntax of OCaml and do not have enough Erlang knowledge to make a judgment on it yet. Because of its consistent and beautiful (non-)syntax, I really like Scheme. However, I really do appreciate the stateless nature of purely functional programming languages such as Haskell. Haskell looks very interesting, but the amount of inconsistent and non-extendable syntax really bothered me. In the interest of preventing a Lisp vs Haskell flame war, just pretend that I can't use Haskell for some other reason. Therefore, my question is: Are there any purely functional Schemes (or Lisps in general)?

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• argv[1] loadImage problem xcode 3.2 and snow leopard

  - by ignacionieto

  Hi Im on mac snow leopard and test these code on xcode3.2 of the Learning OpenCV everything works fine but the image doesnt appear and in the windows. I had try to understand searching for two days what does argv[1] means, but Im still no clear. Im a newbie en C++. I had the image in the same directory where the main.cpp is #include <OpenCV/cv.h> #include <OpenCV/highgui.h> int main(int argc, char** argv) { IplImage* interest_img; CvRect interest_rect; if( argc == 7 && ((interest_img= cvLoadImage( argv[1],1) ) != 0 )) { A more easy example is here: http://books.google.cl/books?id=seAgiOfu2EIC&pg=PA17&lpg=PA17&dq=cvLoadImage%28argv[1]&source=bl&ots=hRJ5bhkAOf&sig=gyYAqZBnS6lCCXJz9Fz7vzOsF-U&hl=es&ei=dvdvS-fWG8eWtgePy_WCBg&sa=X&oi=book_result&ct=result&resnum=6&ved=0CBwQ6AEwBTgK#v=onepage&q=cvLoadImage%28argv[1]&f=false both I have test it but they dont work. Please help me

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• Ruby on Rails - where to write business logic while processing a request? (newbie)

  - by Genadinik

  I am learning Ruby on Rails. I made a simple link like this: <%= link_to "Alex Link", alexes_path(@alex) %> then I routed it in routes.rb like this: resources :alexes get "home/index" then I am a bit unclear, but I think it goes to this part of the controller: def index #@alexes = Alex.all respond_to do |format| format.html # index.html.erb format.json { render json: @alexes } end end Am I correct that it goes to this part of the controller? Then nothing much happens and it goes to the next page which is index.html.rb under views\alexes So what I am wondering is - if I needed to do some business logic, would I write that in the controller snippet? Where inside the snippet? An example would be nice to take a look. Also, I would like to connect to a MongoDb database. Would I also write that in the middle of the controller? Thanks!

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• Why are the contents of my UITableViewCell disappearing?

  - by barfoon

  Hey everyone, I am learning about using the checkmark cell accessory and am wondering why the contents of my cell is disappearing when toggling it. Here is my code: + (void) toggleCheckmarkedCell:(UITableViewCell *)cell { if (cell.accessoryType == UITableViewCellAccessoryNone) cell.accessoryType = UITableViewCellAccessoryCheckmark; else cell.accessoryType = UITableViewCellAccessoryNone; } And here is didSelectRowAtIndexPath: UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath]; [cell setSelectionStyle:UITableViewCellSelectionStyleNone]; [RootViewController toggleCheckmarkedCell:cell]; The checkmark is toggling on/off and is visible but the main contents of the cell disappears. Can anyone explain why this is happening? Thank you,

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• nested form & habtm

  - by brewster

  so i am trying to save to a join table in a habtm relationship, but i am having problems. from my view, i pass in a group id with: = link_to "Create New User", new_user_url(:group => 1) User model (user.rb) class User < ActiveRecord::Base has_and_belongs_to_many :user_groups accepts_nested_attributes_for :user_groups end UserGroups model (user_groups.rb) class UserGroup < ActiveRecord::Base has_and_belongs_to_many :users end users_controller.rb def new @user = User.new(:user_group_ids => params[:group]) end in the new user view, i have access to the User.user_groups object, however when i submit the form, not only does it not save into my join table (user_groups_users), but the object is no longer there. all the other objects & attributes of my User object are persistent except for the user group. i just started learning rails, so maybe i am missing something conceptually here, but i have been really struggling with this.

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• Reuse ASP.NET Control Multiple Times on Page

  - by macinjosh

  I feel somewhat foolish asking such a simple question, but I can't seem to find an answer. I'm new to ASP.NET (C#), but I'm learning by building a simple set of web pages that display a report. I have a variable that represents a company name. I need to output this variable in multiple places on the web page. The only way I have found to output a variable this is with: company_name.Text = "Acme Windows"; then <asp:literal id="company_name" runat="server" /> My problem is that I want to use company_name in multiple places on the page. Do I really have to create a separate variable holding the the same value for each time it is placed on the page? If I just copy the above XML code to all the places I want to show the variable it obviously creates a compile error since that ID is already defined. I feel like I'm missing something very obvious.

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• Scala class to implement two Java Interfaces - how?

  - by puudeli

  Hi, I have just started learning Scala and I'm now wondering how I could implement two different Java interfaces with one Scala class? Let's say I have the following interfaces written in Java public interface EventRecorder { public void abstract record(Event event); } public interface TransactionCapable { public void abstract commit(); } But a Scala class can extend only one class at a time. How can I have a Scala class that could fulfill both contracts? Do I have to map those interfaces into traits? Note, my Scala classes would be used from Java as I am trying to inject new functionality written in Scala into an existing Java application. And the existing framework expects that both interface contracts are fulfilled.

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