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• Do you leverage the benefits of the open-closed principle?

  - by Kaleb Pederson

  The open-closed principle (OCP) states that an object should be open for extension but closed for modification. I believe I understand it and use it in conjunction with SRP to create classes that do only one thing. And, I try to create many small methods that make it possible to extract out all the behavior controls into methods that may be extended or overridden in some subclass. Thus, I end up with classes that have many extension points, be it through: dependency injection and composition, events, delegation, etc. Consider the following a simple, extendable class: class PaycheckCalculator { // ... protected decimal GetOvertimeFactor() { return 2.0M; } } Now say, for example, that the OvertimeFactor changes to 1.5. Since the above class was designed to be extended, I can easily subclass and return a different OvertimeFactor. But... despite the class being designed for extension and adhering to OCP, I'll modify the single method in question, rather than subclassing and overridding the method in question and then re-wiring my objects in my IoC container. As a result I've violated part of what OCP attempts to accomplish. It feels like I'm just being lazy because the above is a bit easier. Am I misunderstanding OCP? Should I really be doing something different? Do you leverage the benefits of OCP differently? Update: based on the answers it looks like this contrived example is a poor one for a number of different reasons. The main intent of the example was to demonstrate that the class was designed to be extended by providing methods that when overridden would alter the behavior of public methods without the need for changing internal or private code. Still, I definitely misunderstood OCP.

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• Composing programs from small simple pieces: OOP vs Functional Programming

  - by Jay Godse

  I started programming when imperative programming languages such as C were virtually the only game in town for paid gigs. I'm not a computer scientist by training so I was only exposed to Assembler and Pascal in school, and not Lisp or Prolog. Over the 1990s, Object-Oriented Programming (OOP) became more popular because one of the marketing memes for OOP was that complex programs could be composed of loosely coupled but well-defined, well-tested, cohesive, and reusable classes and objects. And in many cases that is quite true. Once I learned object-oriented programming my C programs became better because I structured them more like classes and objects. In the last few years (2008-2014) I have programmed in Ruby, an OOP language. However, Ruby has many functional programming (FP) features such as lambdas and procs, which enable a different style of programming using recursion, currying, lazy evaluation and the like. (Through ignorance I am at a loss to explain why these techniques are so great). Very recently, I have written code to use methods from the Ruby Enumerable library, such as map(), reduce(), and select(). Apparently this is a functional style of programming. I have found that using these methods significantly reduce code volume, and make my code easier to debug. Upon reading more about FP, one of the marketing claims made by advocates is that FP enables developers to compose programs out of small well-defined, well-tested, and reusable functions, which leads to less buggy code, and low code volume. QUESTIONS: Is the composition of complex program by using FP techniques contradictory to or complementary to composition of a complex program by using OOP techniques? In which situations is OOP more effective, and when is FP more effective? Is it possible to use both techniques in the same complex program? Do the techniques overlap or contradict each other?

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• How often is seq used in Haskell production code?

  - by Giorgio

  I have some experience writing small tools in Haskell and I find it very intuitive to use, especially for writing filters (using interact) that process their standard input and pipe it to standard output. Recently I tried to use one such filter on a file that was about 10 times larger than usual and I got a Stack space overflow error. After doing some reading (e.g. here and here) I have identified two guidelines to save stack space (experienced Haskellers, please correct me if I write something that is not correct): Avoid recursive function calls that are not tail-recursive (this is valid for all functional languages that support tail-call optimization). Introduce seq to force early evaluation of sub-expressions so that expressions do not grow to large before they are reduced (this is specific to Haskell, or at least to languages using lazy evaluation). After introducing five or six seq calls in my code my tool runs smoothly again (also on the larger data). However, I find the original code was a bit more readable. Since I am not an experienced Haskell programmer I wanted to ask if introducing seq in this way is a common practice, and how often one will normally see seq in Haskell production code. Or are there any techniques that allow to avoid using seq too often and still use little stack space?

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• Is StackOverflow making me stupid? [closed]

  - by Ayush Goyal

  Possible Duplicate: When stuck, how quickly should one resort to Stack Overflow? Its good that solution to almost every programming problem is available at my disposal, either someone has asked it before or programming gurus are waiting for me to post it..sometimes its just the matter of seconds after posting the question and someone points out the error-causing-line or proposes alternate (easier, lightweight and efficient) solution. But today it struck me "is this making me dumb?" In good (umm..not so good) old days I used to figure out the source of my problem and then work it out myself, though it used to eat up lot of time but it helped in developing my logical thinking as it used to make an impression in my mind due to which I tend to avoid that situation in future codes. Now, as soon as I encounter a problem I just give it a shot or two and head towards the community. Many times after looking at the solution it turns out that answer was all in front of me..all I needed was to take a break, hover it once and its solved. Both the approaches make me feel guilty, for wasting time when I could have asked and solved it within minutes OR being too lazy to look over it again before posting the code snippet.

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• How to disable an "always there" program if it isn't in the processes list?

  - by rumtscho

  I have Crashplan and it is constantly running in the background and making backups every 15 minutes. It caused some problems with the backup target folders, so I want it to be inactive while I am making changes to these folders. I started the application itself, but could not find some kind of "Pause" button. So I decided to just stop its process. I first tried the lazy way - the system monitor in the Gnome panel has a "Processes" tab - but didn't find it listed there. Then I did a sudo ps -A and read through the whole list. I don't recognize everything on the list (many process names are self-explaining, like evolution-alarm, but I don't recognize others like phy0) but there was nothing which sounded even remotely like crashplan. But I know that there must have been a process belonging to Crashplan running at this time, because the main Crashplan window was open when I ran the command. Do you have any advice how to stop this thing from running? The best solution would involve temporary preventing it from loading on boot too, since I may need to reboot while doing the maintenance there.

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• Architecture : am I doing things right?

  - by Jeremy D

  I'm trying to use a '~classic' layered arch using .NET and Entity Framework. We are starting from a legacy database which is a little bit crappy: Inconsistent naming Unneeded views (view referencing other views, select * views etc...) Aggregated columns Potatoes and Carrots in the same table etc... So I ended with fully isolating my database structure from my domain model. To do so EF entities are hidden from presentation layer. The goal is to permit an easier database refactoring while lowering the impact of it on applications. I'm now facing a lot of challenges and I'm starting to ask myself if I'm doing things right. My Domain Model is highly volatile, it keeps evolving with apps as new fields needs are arising. Complexity of it keeps raising and class it contains start to get a lot of properties. Creating include strategy and reprojecting to EF is very tricky (my domain objects don't have any kind of lazy/eager loading relationship properties): DomainInclude<Domain.Model.Bar>.Include("Customers").Include("Customers.Friends") // To... IFooContext.Bars.Include(...).Include(...).Where(...) Some framework are raping the isolation levels (Devexpress Grids which needs either XPO or IQueryable for filtering and paging large data sets) I'm starting to ask myself if : the isolation of EF auto-generated entities is an unneeded cost. I should allow frameworks to hit IQueryable? Slow slope to hell? (it's really hard to isolate DevExpress framework, any successful experience?) the high volatility of my domain model is normal? Did you have similar difficulties? Any advice based on experience?

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• Obtain reference to Parent object during instantiation

  - by GoldBishop

  I have a situation where a custom class is a property of another class. What i need to be able to do, if it is possible at all, is obtain a reverse to the "parent" class (ie the the class that holds the current class as a property). For Instance: Public Class Class1 ... public readonly property Prop11 as Class2 public property Prop12 as String ... End Class Public Class Class2 ... private _par as Class1 private _var21 as string ... Public Sub New(...) me._par = ???? ... End Sub public readonly property Prop21 as string Get return me._par.Prop12 & me._var21 End Get End Property ... End Class Ultimately, i am trying to access other properties within Class1 from Class2 as they do have substance for information from within Class2. There are several other classes within Class1 that provide descriptive information to other classes contained within it as properties but the information is not extensible to all of the classes through Inheritance, as Class1 is being used as a resource bin for the property classes and the application itself. Diagram, lazy design ;): Application <- Class1.Prop12 Application <- Class1.Prop11.Prop21 Question: Is it possible to get a recursion through this design setup?

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• Would form keys reduce the amount of spam we receive?

  - by David Wilkins

  I work for a company that has an online store, and we constantly have to deal with a lot of spam product reviews, and bogus customer accounts. These are all created by automated systems and are more of a nuisance than anything. What I am thinking of (in lieu of captcha, which can be broken) is adding a sort of form key solution to all relevant forms. I know for certain some of the spammers are using XRumer, and I know they seldom request a page before sending us the form data (Is this the definition of CSRF?) so I would think that tying a key to each requested form would at least stem the tide. I also know the spammers are lazy and don't check their work, or they would see that we have never posted a spam review, and they have never gained any revenue from our site. Would this succeed in significantly reducing the volume of spam product reviews and customer account creations we are seeing? EDIT: To clarify what I mean by "Form Keys": I am referring to creating a unique identifier (or "key") that will be used as an invisible, static form field. This key will also be stored either in the database (relative to the user session) or in a cookie variable. When the form's target gets a request, the key must be validated for the form's data to be processed. Those pesky bots won't have the key because they don't load the javascript that generates the form (they just send a blind request to the target) and even if they did load the javascript once, they'd only have one valid key, and I'm not sure they even use cookies.

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• Alternatives to type casting in your domain

  - by Mr Happy

  In my Domain I have an entity Activity which has a list of ITasks. Each implementation of this task has it's own properties beside the implementation of ITask itself. Now each operation of the Activity entity (e.g. Execute()) only needs to loop over this list and call an ITask method (e.g. ExecuteTask()). Where I'm having trouble is when a specific tasks' properties need to be updated. How do I get an instance of that task? The options I see are: Get the Activity by Id and cast the task I need. This'll either sprinkle my code with: Tasks.OfType<SpecificTask>().Single(t => t.Id == taskId) or Tasks.Single(t => t.Id == taskId) as SpecificTask Make each task unique in the whole system (make each task an entity), and create a new repository for each ITask implementation I don't like either option, the first because I don't like casting: I'm using NHibernate and I'm sure this'll come back and bite me when I start using Lazy Loading (NHibernate currently uses proxies to implement this). I don't like the second option because there are/will be dozens of different kind of tasks. Which would mean I'd have to create as many repositories. Am I missing a third option here? Or are any of my objections to the two options not justified? How have you solved this problem in the past?

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• Want Google to index redirect urls

  - by Dave Goten

  I'm having issues with users who think that Google Search is the address bar. Some of the sites that link to my site use user friendly addresses with 301 redirects to pages that have less friendly URLs. So, for example if I enter www.foo.com/bar it goes to www.bar.com/page.php?some-parameters-and-utm-codes-etc usually this is done by a 301 redirect in order to keep the SEO from foo.com on bar.com and so on, which I believe is standard practice. However, lately there have been more and more people searching www.foo.com/bar instead of going to www.foo.com/bar directly and because the page /bar is nothing more than a redirect it has no SEO that I know of. Things I've thought of but haven't been able to test, because Google takes forever to update :) (and I'm lazy like that), include using Google sitemaps and having them enter their redirects as entries there. (I could see this working if they were the top search entry all the time, and it might appear as a sitelink, but I don't know if that'll make the url itself show up in searches) Using Canonical tags on my pages to the redirects they set up. Which is a nightmare in itself because of the nature of my pages. One week the www.foo.com/bar might go to www.bar.com/pageA.php the next it might goto www.bar.com/pageB.php and having to remember to take the canonical tag off of pageA, so that it doesn't get confused with pageB would be a pain. Using 302 redirects -.- So I guess the question here is, does anyone have any experience or knowledge about this? What should I do to make www.foo.com/bar show up when someone 'searches' for this redirect url?

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• Using template questions in a technical interview

  - by Desolate Planet

  I've recently been in an argument with a colleague about technical questions in interviews. As a graduate, I went round lots of companies and noticed they used the same questions. An example is "Can you write a function that determines if a number is prime or not?", 4 years later, I find that particular question is quite common even for a junior developer. I might not be looking at this the correct way, but shouldn't software houses be intelligent enough to think up their own interview questions? I've been to about 16 interviews as a graduate and the same questions came up in about 75% of them. This leads me to believe that many companies are lazy and simply Google: 'Template questions for interviewing software developers' and I look down on that. Question: Is it better to use a set of questions off some template or should software houses strive to be more original and come up with their own interview material? From my point of view, if I failed an interview and went off and looked for good answers to the questions I messed up on, I could fly through the next interview if the questions are the same.

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• [EF + Oracle]Object Context

  - by JTorrecilla

  Prologue After EF episodes I and II, we are going to see the Object Context. What is Object Context? It is a class which manages the DB connection, and the different Entities of our model. When Visual Studio creates the EF model, like I explain previously, also generates a Class that extends ObjectContext. ObjectContext provides: - DB connection - Add, update and delete functions. - Object Sets of Entities. - State of Pending Changes. This class will give a function, for each Entity, like  Esta clase va a contar con una función, para cada entidad, del tipo “AddTo{ENTITY}({Entity_Type } value)”, which are going to add a Entity to the related ObjectSet. In addition, it has a property, for each Entity, like “ObjectSet<TEntity> Entity”, does will keep the related record set. It will be filled with the CreateObjectSet<TEntity> function of Base class (ObjectContext). What is an ObjectSet? It is a class that allows us to manage the Entity Set from a Type. It inherits from: · ObjectQuery<TEntity> · IObjectSet<TEntity> · IQueryAble<TEntity · IEnumerable<TEntity · IQueryAble · IEnumerable An ObjectSet is a class property that allows query, insert, delete and update records from a determinate Entity. In following chapters we will see how to query Entities. LazyLoadingEnabled A very important property of the Context is “LazyLoadingEnabled”. This Boolean property lets indicate if the data loading is lazy, in other words, the Object will not be created and query until not be needed. Finally In this post we have seen what the VS generated context is, some of the characteristics, and where to see Entity data. In next chapters we will see, CRUD operations, and how to query ObjectSets.

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• What is the average page size for single page application (SPA)? [on hold]

  - by Emmanuel Istace

  I'm developing a single page application with a lot of css & javascript. For now the page is 1.3Mo composed by 5 section. Here are the rounded stats : Document : 10kb Style : 60kb Images : 450 kb (already compressed, include a big gallery thumbnails) Javascript : 700kb - 600kb of "framework" (jquery, jquery-ui, boostrap, modernizer, waypoint, ...) and 100kb of custom js. Fonts : 125kb And the site is not finished yet. (Will include gmap api, and some others...) My questions are : Do you have any statistics about the average weight of an SPA? As this is the whole website, do you think it's acceptable? Is lazy load (for images) a solution? What will be impact for SEO ? Is the "200kb rule" of google still relevant? Do you know great tools to detect which javascript code is not used during the the exection of a page and then the availability to optimize these 700kb of framework js stuffs? Can a caching strategy be an answer?

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• Continuous Retraining Tutorials

  - by foampile

  I am looking for an online resource in which you can sortof design your future professional profile and it would provide you a set of tutorials that you would complete to get a basic level of familiarity with related technologies. One of my professional problems is my learning style: I can learn either by direct hands-on experience OR by following a rigid training program that goes in a linear progression. I have a hard time learning things in a multidimensional environment where the biggest challenge is to determine what needs to be learned and how to pick from a ton of books and the least problem is to go through the actual material. So I am looking for a reputable source that will knock those two confusing questions out for me so I can kick back and continuously be upgrading my skills without having to worry about what and how myself. I have found some decent online tutorials for various technologies but never found a single place that has all or most developer education tutorials that all follow the same or similar interface. I am kindof a lazy learner and would rather follow confirmed learning steps than be figuring my own education path just to realize I did it all wrong down the road. Is there a tutorial mega-boutique like that online?

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• Where is the best place to teach myself a language, and which one?

  - by Lorinda

  Hello, I do not know any programming languages at all. I will self teach myself and need to know the best place to do so where I can learn from a most basic level. Where is a great place to begin learning a language? What language is best to learn first? Is it silly to learn Ruby first? Here, I came across someone saying that learning some of the higher languages can make you 'lazy' if you learn them first. Like Ruby amongst others. For my first language, my husband is advising me to learn Ruby (for his own personal interests). However, I need some independent advice of how to get started and what language I should learn first. I will eventually learn Ruby and then Rails. Four months ago, my husband ordered a text of objective C because he thought he would take it on. I flipped through and it was clearly starting at a place more advanced than where I am coming from. I have dabbled with a Ruby tutorial and I don't get it. I get what I am putting in is what I get, but I don't understand what is leading up to that. I need to know ALL the rules first. I then looked up computer languages and stared researching binary code which helped a lot, but not where I want to start. I don't have a lot of time right now in my life (with four kids) to go back that far. If I were going to school, that would be different. Any advice you could give is most welcomed.

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• RequireJS: JavaScript for the Enterprise

  - by Geertjan

  I made a small introduction to RequireJS via some of the many cool new RequireJS features in NetBeans IDE. I believe RequireJS, and the modularity and encapsulation and loading solutions that it brings, provides the tools needed for creating large JavaScript applications, i.e., enterprise JavaScript applications. &amp;amp;lt;span id=&amp;amp;quot;XinhaEditingPostion&amp;amp;quot;&amp;amp;gt;&amp;amp;lt;/span&amp;amp;gt; (Sorry for the wobbly sound in the above.) An interesting comment by my colleague John Brock on the above: One other advantage that RequireJS brings, is called lazy loading of resources. In your first example, everyone one of those .js files is loaded when the first file is loaded in the browser. By using the require() call in your modules, your application will only load the javascript modules when they are actually needed. It makes for faster startup in large applications. You could show this by showing the libraries that are loaded in the Network Monitor window. So I did as suggested: Click the screenshot to enlarge it and notice how the Network Monitor is helpful in the context of RequireJS troubleshooting.

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• Which hard disk drive is which?

  - by djeikyb

  I want to know which hard disk drive corresponds to which device path. It's trivial to match the hard disk stats (brand, size) with the dev path, but I want more. I want to know which drive is which inside my case. What's a good way to go about getting this info? Rules: I am a lazy bum. I don't want to tear apart my server to remove all the drives, then add back one by one. A reboot is acceptable. The drives are inconveniently scrunched together in the case. All label information is hidden. The case can be opened. Most disks are SATA, so theoretically hot swappable. Unplugging cables is fair game. Bonus: For a cli only solution. I'll award answer to the best/easiest gui or cli answer, and give a bounty to the next-best answer of the other kind. Or maybe the other way around, because the bounty is worth more points.

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• Showing an Action on a TopComponent Node

  - by Geertjan

  Let's say you want to extend the tools in NetBeans IDE, specifically for TopComponents. When the user right-clicks in the Projects window (or Files window or Favorites window) on a Java class that extends TopComponent, a menu item should be available for branding the TopComponent. What "branding" entails is, at this stage, a secondary question. The primary question, from an implementation point of view, is "how do I create an action that is only shown when the user right-clicks on a TopComponent?" Here's the solution, in NetBeans IDE 7.2 (the "lazy" attribute, here set to false, is new in 7.2): import com.sun.source.tree.ClassTree; import com.sun.source.util.TreePathScanner; import java.awt.event.ActionEvent; import java.io.IOException; import javax.lang.model.element.Element; import javax.lang.model.element.TypeElement; import javax.swing.AbstractAction; import javax.swing.Action; import javax.swing.JOptionPane; import org.netbeans.api.java.source.CompilationController; import org.netbeans.api.java.source.CompilationInfo; import org.netbeans.api.java.source.JavaSource; import org.netbeans.api.java.source.JavaSource.Phase; import org.netbeans.api.java.source.Task; import org.openide.awt.ActionID; import org.openide.awt.ActionReference; import org.openide.awt.ActionReferences; import org.openide.awt.ActionRegistration; import org.openide.awt.DynamicMenuContent; import org.openide.loaders.DataObject; import org.openide.util.ContextAwareAction; import org.openide.util.Exceptions; import org.openide.util.Lookup; import org.openide.util.NbBundle.Messages; import org.openide.util.Utilities; @ActionID(     category = "Tools", id = "org.tc.customizer.BrandTopComponentAction") @ActionRegistration(     displayName = "#CTL_BrandTopComponentAction",     lazy = false) @ActionReferences({     @ActionReference(path = "Loaders/text/x-java/Actions", position = 150) }) @Messages("CTL_BrandTopComponentAction=Brand") public final class BrandTopComponentAction extends AbstractAction implements ContextAwareAction {     private final DataObject dobj;     public BrandTopComponentAction() {         this(Utilities.actionsGlobalContext());     }     public BrandTopComponentAction(Lookup context) {         super(Bundle.CTL_BrandTopComponentAction());         this.dobj = context.lookup(DataObject.class);         //Enable the menu item only if we're dealing with a TopComponent         JavaSource javaSource = JavaSource.forFileObject(dobj.getPrimaryFile());         try {             javaSource.runUserActionTask(new ScanForTopComponentTask(this), true);         } catch (IOException ex) {             Exceptions.printStackTrace(ex);         }         //Hide the menu item if it isn't enabled:         putValue(DynamicMenuContent.HIDE_WHEN_DISABLED, true);     }     @Override     public void actionPerformed(ActionEvent ev) {         JOptionPane.showMessageDialog(null, "Hurray, I am a TopComponent!");         //Now add your code for showing a dialog,         //where the dialog will display UI for branding the TopComponent somehow         //and retrieve those branding values         //and then change the TopComponent class accordingly.     }     @Override     public Action createContextAwareInstance(Lookup actionContext) {         return new BrandTopComponentAction(actionContext);     }     private static class ScanForTopComponentTask implements Task<CompilationController> {         private final BrandTopComponentAction action;         private ScanForTopComponentTask(BrandTopComponentAction action) {             this.action = action;         }         @Override         public void run(CompilationController compilationController) throws Exception {             compilationController.toPhase(Phase.ELEMENTS_RESOLVED);             new MemberVisitor(compilationController, action).scan(                     compilationController.getCompilationUnit(), null);         }     }     private static class MemberVisitor extends TreePathScanner<Void, Void> {         private CompilationInfo info;         private final AbstractAction action;         public MemberVisitor(CompilationInfo info, AbstractAction action) {             this.info = info;             this.action = action;         }         @Override         public Void visitClass(ClassTree t, Void v) {             Element el = info.getTrees().getElement(getCurrentPath());             if (el != null) {                 TypeElement te = (TypeElement) el;                 if (te.getSuperclass().toString().equals("org.openide.windows.TopComponent")){                     action.setEnabled(true);                 } else {                     action.setEnabled(false);                 }             }             return null;         }     } } The code above is the result of combining various tutorials found on the NetBeans Platform Learning Trail.

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• How do I create an efficient long, pannable, sprite-animated scene in a Windows Store game?

  - by Groo

  I am creating my first Windows Store application in XAML, and I cannot seem to find a proper example for the requirements I have. The basic idea of the app is to have a large scrollable canvas which would lazily start animating visible parts of the view as soon as user stops panning over a certain content (with some audio played also): My original idea was to use a StackPanel to add a bunch of custom controls, each of which would then animate itself once visible (with a short delay), but I have a couple of concerns: If the entire canvas is ~50 screen widths wide, is it feasible to load all content at the beginning, or do I need to plan doing some lazy loading during scrolling? For example, when I select a certain region in the Bing Travel app, it seems to lazily load tiles as I scroll it towards the end. Since content is stretched 100% vertically, and these animations are vectorized to be resolution independent, I am not sure if XAML (CompositionTarget) will be able to handle this, or I have to go for DirectX (MonoGame or C++) to get rid of flicker. Even better, is there an example for Windows 8 which uses a 100% vertically sized GridView with custom animated controls inside?

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• Dynamic XAP loading in Task-It - Part 1

  Download Source Code NOTE 1: The source code provided is running against the RC versions of Silverlight 4 and VisualStudio 2010, so you will need to update to those bits to run it. NOTE 2: After downloading the source, be sure to set the .Web project as the StartUp Project, and Default.aspx as the Start Page In my MEF into post, MEF to the rescue in Task-It, I outlined a couple of issues I was facing and explained why I chose MEF (the Managed Extensibility Framework) to solve these issues. Other posts to check out There are a few other resources out there around dynamic XAP loading that you may want to review (by the way, Glenn Block is the main dude when it comes to MEF): Glenn Blocks 3-part series on a dynamically loaded dashboard Glenn and John Papas Silverlight TV video on dynamic xap loading These provide some great info, but didnt exactly cover the scenario I wanted to achieve in Task-Itand that is dynamically loading each of the apps pages the first time the user enters a page. The code In the code I provided for download above, I created a simple solution that shows the technique I used for dynamic XAP loading in Task-It, but without all of the other code that surrounds it. Taking all that other stuff away should make it easier to grasp. Having said that, there is still a fair amount of code involved. I am always looking for ways to make things simpler, and to achieve the desired result with as little code as possible, so if I find a better/simpler way I will blog about it, but for now this technique works for me. When I created this solution I started by creating a new Silverlight Navigation Application called DynamicXAP Loading. I then added the following line to my UriMappings in MainPage.xaml: <uriMapper:UriMapping Uri="/{assemblyName};component/{path}" MappedUri="/{assemblyName};component/{path}"/> In the section of MainPage.xaml that produces the page links in the upper right, I kept the Home link, but added a couple of new ones (page1 and page 2). These are the pages that will be dynamically (lazy) loaded: <StackPanel x:Name="LinksStackPanel" Style="{StaticResource LinksStackPanelStyle}">      <HyperlinkButton Style="{StaticResource LinkStyle}" NavigateUri="/Home" TargetName="ContentFrame" Content="home"/>      <Rectangle Style="{StaticResource DividerStyle}"/>      <HyperlinkButton Style="{StaticResource LinkStyle}" Content="page 1" Command="{Binding NavigateCommand}" CommandParameter="{Binding ModulePage1}"/>      <Rectangle Style="{StaticResource DividerStyle}"/>      <HyperlinkButton Style="{StaticResource LinkStyle}" Content="page 2" Command="{Binding NavigateCommand}" CommandParameter="{Binding ModulePage2}"/>  </StackPanel> In App.xaml.cs I added a bit of MEF code. In Application_Startup I call a method called InitializeContainer, which creates a PackageCatalog (a MEF thing), then I create a CompositionContainer and pass it to the CompositionHost.Initialize method. This is boiler-plate MEF stuff that allows you to do 'composition' and import 'packages'. You're welcome to do a bit more MEF research on what is happening here if you'd like, but for the purpose of this example you can just trust that it works. :-) private void Application_Startup(object sender, StartupEventArgs e) {     InitializeContainer();     this.RootVisual = new MainPage(); }   private static void InitializeContainer() {     var catalog = new PackageCatalog();     catalog.AddPackage(Package.Current);     var container = new CompositionContainer(catalog);     container.ComposeExportedValue(catalog);     CompositionHost.Initialize(container); } Infrastructure In the sample code you'll notice that there is a project in the solution called DynamicXAPLoading.Infrastructure. This is simply a Silverlight Class Library project that I created just to move stuff I considered application 'infrastructure' code into a separate place, rather than cluttering the main Silverlight project (DynamicXapLoading). I did this same thing in Task-It, as the amount of this type of code was starting to clutter up the Silverlight project, and it just seemed to make sense to move things like Enums, Constants and the like off to a separate place. In the DynamicXapLoading.Infrastructure project you'll see 3 classes: Enums - There is only one enum in here called ModuleEnum. We'll use these later. PageMetadata - We will use this class later to add metadata to a new dynamically loaded project. ViewModelBase - This is simply a base class for view models that we will use in this, as well as future samples. As mentioned in my MVVM post, I will be using the MVVM pattern throughout my code for reasons detailed in the post. By the way, the ViewModelExtension class in there allows me to do strongly-typed property changed notification, so rather than OnPropertyChanged("MyProperty"), I can do this.OnPropertyChanged(p => p.MyProperty). It's just a less error-prown approach, because if you don't spell "MyProperty" correctly using the first method, nothing will break, it just won't work. Adding a new page We currently have a couple of pages that are being dynamically (lazy) loaded, but now let's add a third page. 1. First, create a new Silverlight Application project: In this example I call it Page3. In the future you may prefer to use a different name, like DynamicXAPLoading.Page3, or even DynamicXAPLoading.Modules.Page3. It can be whatever you want. In my Task-It application I used the latter approach (with 'Modules' in the name). I do think of these application as 'modules', but Prism uses the same term, so some folks may not like that. Use whichever naming convention you feel is appropriate, but for now Page3 will do. When you change the name to Page3 and click OK, you will be presented with the Add New Project dialog: It is important that you leave the 'Host the Silverlight application in a new or existing Web site in the solution' checked, and the .Web project will be selected in the dropdown below. This will create the .xap file for this project under ClientBin in the .Web project, which is where we want it. 2. Uncheck the 'Add a test page that references the application' checkbox, and leave everything else as is. 3. Once the project is created, you can delete App.xaml and MainPage.xaml. 4. You will need to add references your new project to the following: DynamicXAPLoading.Infrastructure.dll (this is a Project reference) DynamicNavigation.dll (this is in the Libs directory under the DynamicXAPLoading project) System.ComponentModel.Composition.dll System.ComponentModel.Composition.Initialization.dll System.Windows.Controls.Navigation.dll If you have installed the latest RC bits you will find the last 3 dll's under the .NET tab in the Add Referenced dialog. They live in the following location, or if you are on a 64-bit machine like me, it will be Program Files (x86).       C:\Program Files\Microsoft SDKs\Silverlight\v4.0\Libraries\Client Now let's create some UI for our new project. 5. First, create a new Silverlight User Control called Page3.dyn.xaml 6. Paste the following code into the xaml: <dyn:DynamicPageShim xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"     xmlns:dyn="clr-namespace:DynamicNavigation;assembly=DynamicNavigation"     xmlns:my="clr-namespace:Page3;assembly=Page3">     <my:Page3Host /> </dyn:DynamicPageShim> This is just a 'shim', part of David Poll's technique for dynamic loading. 7. Expand the icon next to Page3.dyn.xaml and delete the code-behind file (Page3.dyn.xaml.cs). 8. Next we will create a control that will 'host' our page. Create another Silverlight User Control called Page3Host.xaml and paste in the following XAML: <dyn:DynamicPage x:Class="Page3.Page3Host"     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"     xmlns:dyn="clr-namespace:DynamicNavigation;assembly=DynamicNavigation"     xmlns:Views="clr-namespace:Page3.Views"      mc:Ignorable="d"     d:DesignHeight="300" d:DesignWidth="400"     Title="Page 3">       <Views:Page3/>   </dyn:DynamicPage> 9. Now paste the following code into the code-behind for this control: using DynamicXAPLoading.Infrastructure;   namespace Page3 {     [PageMetadata(NavigateUri = "/Page3;component/Page3.dyn.xaml", Module = Enums.Page3)]     public partial class Page3Host     {         public Page3Host()         {             InitializeComponent();         }     } } Notice that we are now using that PageMetadata custom attribute class that we created in the Infrastructure project, and setting its two properties. NavigateUri - This tells it that the assembly is called Page3 (with a slash beforehand), and the page we want to load is Page3.dyn.xaml...our 'shim'. That line we added to the UriMapper in MainPage.xaml will use this information to load the page. Module - This goes back to that ModuleEnum class in our Infrastructure project. However, setting the Module to ModuleEnum.Page3 will cause a compilation error, so... 10. Go back to that Enums.cs under the Infrastructure project and add a 3rd entry for Page3: public enum ModuleEnum {     Page1,     Page2,     Page3 } 11. Now right-click on the Page3 project and add a folder called Views. 12. Right-click on the Views folder and create a new Silverlight User Control called Page3.xaml. We won't bother creating a view model for this User Control as I did in the Page 1 and Page 2 projects, just for the sake of simplicity. Feel free to add one if you'd like though, and copy the code from one of those other projects. Right now those view models aren't really doing anything anyway...though they will in my next post. :-) 13. Now let's replace the xaml for Page3.xaml with the following: <dyn:DynamicPage x:Class="Page3.Views.Page3"     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"     xmlns:dyn="clr-namespace:DynamicNavigation;assembly=DynamicNavigation"     mc:Ignorable="d"     d:DesignHeight="300" d:DesignWidth="400"     Style="{StaticResource PageStyle}">       <Grid x:Name="LayoutRoot">         <ScrollViewer x:Name="PageScrollViewer" Style="{StaticResource PageScrollViewerStyle}">             <StackPanel x:Name="ContentStackPanel">                 <TextBlock x:Name="HeaderText" Style="{StaticResource HeaderTextStyle}" Text="Page 3"/>                 <TextBlock x:Name="ContentText" Style="{StaticResource ContentTextStyle}" Text="Page 3 content"/>             </StackPanel>         </ScrollViewer>     </Grid>   </dyn:DynamicPage> 14. And in the code-behind remove the inheritance from UserControl, so it should look like this: namespace Page3.Views {     public partial class Page3     {         public Page3()         {             InitializeComponent();         }     } } One thing you may have noticed is that the base class for the last two User Controls we created is DynamicPage. Once again, we are using the infrastructure that David Poll created. 15. OK, a few last things. We need a link on our main page so that we can access our new page. In MainPage.xaml let's update our links to look like this: <StackPanel x:Name="LinksStackPanel" Style="{StaticResource LinksStackPanelStyle}">     <HyperlinkButton Style="{StaticResource LinkStyle}" NavigateUri="/Home" TargetName="ContentFrame" Content="home"/>     <Rectangle Style="{StaticResource DividerStyle}"/>     <HyperlinkButton Style="{StaticResource LinkStyle}" Content="page 1" Command="{Binding NavigateCommand}" CommandParameter="{Binding ModulePage1}"/>     <Rectangle Style="{StaticResource DividerStyle}"/>     <HyperlinkButton Style="{StaticResource LinkStyle}" Content="page 2" Command="{Binding NavigateCommand}" CommandParameter="{Binding ModulePage2}"/>     <Rectangle Style="{StaticResource DividerStyle}"/>     <HyperlinkButton Style="{StaticResource LinkStyle}" Content="page 3" Command="{Binding NavigateCommand}" CommandParameter="{Binding ModulePage3}"/> </StackPanel> 16. Next, we need to add the following at the bottom of MainPageViewModel in the ViewModels directory of our DynamicXAPLoading project: public ModuleEnum ModulePage3 {     get { return ModuleEnum.Page3; } } 17. And at last, we need to add a case for our new page to the switch statement in MainPageViewModel: switch (module) {     case ModuleEnum.Page1:         DownloadPackage("Page1.xap");         break;     case ModuleEnum.Page2:         DownloadPackage("Page2.xap");         break;     case ModuleEnum.Page3:         DownloadPackage("Page3.xap");         break;     default:         break; } Now fire up the application and click the page 1, page 2 and page 3 links. What you'll notice is that there is a 2-second delay the first time you hit each page. That is because I added the following line to the Navigate method in MainPageViewModel: Thread.Sleep(2000); // Simulate a 2 second initial loading delay The reason I put this in there is that I wanted to simulate a delay the first time the page loads (as the .xap is being downloaded from the server). You'll notice that after the first hit to the page though that there is no delay...that's because the .xap has already been downloaded. Feel free to comment out this 2-second delay, or remove it if you'd like. I just wanted to show how subsequent hits to the page would be quicker than the initial one. By the way, you may want to display some sort of BusyIndicator while the .xap is loading. I have that in my Task-It appplication, but for the sake of simplicity I did not include it here. In the future I'll blog about how I show and hide the BusyIndicator using events (I'm currently using the eventing framework in Prism for that, but may move to the one in the MVVM Light Toolkit some time soon). Whew, that felt like a lot of steps, but it does work quite nicely. As I mentioned earlier, I'll try to find ways to simplify the code (I'd like to get away from having things like hard-coded .xap file names) and will blog about it in the future if I find a better way. In my next post, I'll talk more about what is actually happening with the code that makes this all work.Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• Problems debugging using Cygwin gdb in Eclipse CDT(Helios)

  - by Rohan

  I am trying to debug an application using Eclipse CDT and cygwin gdb and I am facing a problem if my code calls Sleep(), it looks like whenever a sleep is encountered in the code the debugger seems to go in an infinite loop(I meant it never terminates or hit a breakpoint after sleep). On pressing pause the code is stuck on one of the thread on sigint::interrupt. Even my debugger console windows throw these error in the console output: [New thread 5968.0x1f98] Error: dll starting at 0x774a0000 not found. Error: dll starting at 0x775c0000 not found. [New thread 5968.0x19e8] Any idea what are these errors about? It would be helpful if someone can help me out here as I am new to eclipse and I am used to using VS so it has made be lazy to be honest and expect things to work out of box. Here are more details if required Windows 7 x64 bit. Eclipse 3.6 Helios with CDT plug-in compiled from the CVS head. Cygwin latest from website, I think it is 1.71

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• How can I eager-load a child collection mapped to a non-primary key in NHibernate 2.1.2?

  - by David Rubin

  Hi, I have two objects with a many-to-many relationship between them, as follows: public class LeftHandSide { public LeftHandSide() { Name = String.Empty; Rights = new HashSet<RightHandSide>(); } public int Id { get; set; } public string Name { get; set; } public ICollection<RightHandSide> Rights { get; set; } } public class RightHandSide { public RightHandSide() { OtherProp = String.Empty; Lefts = new HashSet<LeftHandSide>(); } public int Id { get; set; } public string OtherProp { get; set; } public ICollection<LeftHandSide> Lefts { get; set; } } and I'm using a legacy database, so my mappings look like: Notice that LeftHandSide and RightHandSide are associated by a different column than RightHandSide's primary key. <class name="LeftHandSide" table="[dbo].[lefts]" lazy="false"> <id name="Id" column="ID" unsaved-value="0"> <generator class="identity" /> </id> <property name="Name" not-null="true" /> <set name="Rights" table="[dbo].[lefts2rights]"> <key column="leftId" /> <!-- THIS IS THE IMPORTANT BIT: I MUST USE PROPERTY-REF --> <many-to-many class="RightHandSide" column="rightProp" property-ref="OtherProp" /> </set> </class> <class name="RightHandSide" table="[dbo].[rights]" lazy="false"> <id name="Id" column="id" unsaved-value="0"> <generator class="identity" /> </id> <property name="OtherProp" column="otherProp" /> <set name="Lefts" table="[dbo].[lefts2rights]"> <!-- THIS IS THE IMPORTANT BIT: I MUST USE PROPERTY-REF --> <key column="rightProp" property-ref="OtherProp" /> <many-to-many class="LeftHandSide" column="leftId" /> </set> </class> The problem comes when I go to do a query: LeftHandSide lhs = _session.CreateCriteria<LeftHandSide>() .Add(Expression.IdEq(13)) .UniqueResult<LeftHandSide>(); works just fine. But LeftHandSide lhs = _session.CreateCriteria<LeftHandSide>() .Add(Expression.IdEq(13)) .SetFetchMode("Rights", FetchMode.Join) .UniqueResult<LeftHandSide>(); throws an exception (see below). Interestingly, RightHandSide rhs = _session.CreateCriteria<RightHandSide>() .Add(Expression.IdEq(127)) .SetFetchMode("Lefts", FetchMode.Join) .UniqueResult<RightHandSide>(); seems to be perfectly fine as well. NHibernate.Exceptions.GenericADOException Message: Error performing LoadByUniqueKey[SQL: SQL not available] Source: NHibernate StackTrace: c:\opt\nhibernate\2.1.2\source\src\NHibernate\Type\EntityType.cs(563,0): at NHibernate.Type.EntityType.LoadByUniqueKey(String entityName, String uniqueKeyPropertyName, Object key, ISessionImplementor session) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Type\EntityType.cs(428,0): at NHibernate.Type.EntityType.ResolveIdentifier(Object value, ISessionImplementor session, Object owner) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Type\EntityType.cs(300,0): at NHibernate.Type.EntityType.NullSafeGet(IDataReader rs, String[] names, ISessionImplementor session, Object owner) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Persister\Collection\AbstractCollectionPersister.cs(695,0): at NHibernate.Persister.Collection.AbstractCollectionPersister.ReadElement(IDataReader rs, Object owner, String[] aliases, ISessionImplementor session) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Collection\Generic\PersistentGenericSet.cs(54,0): at NHibernate.Collection.Generic.PersistentGenericSet`1.ReadFrom(IDataReader rs, ICollectionPersister role, ICollectionAliases descriptor, Object owner) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Loader\Loader.cs(706,0): at NHibernate.Loader.Loader.ReadCollectionElement(Object optionalOwner, Object optionalKey, ICollectionPersister persister, ICollectionAliases descriptor, IDataReader rs, ISessionImplementor session) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Loader\Loader.cs(385,0): at NHibernate.Loader.Loader.ReadCollectionElements(Object[] row, IDataReader resultSet, ISessionImplementor session) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Loader\Loader.cs(326,0): at NHibernate.Loader.Loader.GetRowFromResultSet(IDataReader resultSet, ISessionImplementor session, QueryParameters queryParameters, LockMode[] lockModeArray, EntityKey optionalObjectKey, IList hydratedObjects, EntityKey[] keys, Boolean returnProxies) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Loader\Loader.cs(453,0): at NHibernate.Loader.Loader.DoQuery(ISessionImplementor session, QueryParameters queryParameters, Boolean returnProxies) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Loader\Loader.cs(236,0): at NHibernate.Loader.Loader.DoQueryAndInitializeNonLazyCollections(ISessionImplementor session, QueryParameters queryParameters, Boolean returnProxies) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Loader\Loader.cs(1649,0): at NHibernate.Loader.Loader.DoList(ISessionImplementor session, QueryParameters queryParameters) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Loader\Loader.cs(1568,0): at NHibernate.Loader.Loader.ListIgnoreQueryCache(ISessionImplementor session, QueryParameters queryParameters) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Loader\Loader.cs(1562,0): at NHibernate.Loader.Loader.List(ISessionImplementor session, QueryParameters queryParameters, ISet`1 querySpaces, IType[] resultTypes) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Loader\Criteria\CriteriaLoader.cs(73,0): at NHibernate.Loader.Criteria.CriteriaLoader.List(ISessionImplementor session) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Impl\SessionImpl.cs(1936,0): at NHibernate.Impl.SessionImpl.List(CriteriaImpl criteria, IList results) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Impl\CriteriaImpl.cs(246,0): at NHibernate.Impl.CriteriaImpl.List(IList results) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Impl\CriteriaImpl.cs(237,0): at NHibernate.Impl.CriteriaImpl.List() c:\opt\nhibernate\2.1.2\source\src\NHibernate\Impl\CriteriaImpl.cs(398,0): at NHibernate.Impl.CriteriaImpl.UniqueResult() c:\opt\nhibernate\2.1.2\source\src\NHibernate\Impl\CriteriaImpl.cs(263,0): at NHibernate.Impl.CriteriaImpl.UniqueResult[T]() D:\proj\CMS3\branches\nh_auth\DomainModel2Tests\Authorization\TempTests.cs(46,0): at CMS.DomainModel.Authorization.TempTests.Test1() Inner Exception System.Collections.Generic.KeyNotFoundException Message: The given key was not present in the dictionary. Source: mscorlib StackTrace: at System.ThrowHelper.ThrowKeyNotFoundException() at System.Collections.Generic.Dictionary`2.get_Item(TKey key) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Persister\Entity\AbstractEntityPersister.cs(2047,0): at NHibernate.Persister.Entity.AbstractEntityPersister.GetAppropriateUniqueKeyLoader(String propertyName, IDictionary`2 enabledFilters) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Persister\Entity\AbstractEntityPersister.cs(2037,0): at NHibernate.Persister.Entity.AbstractEntityPersister.LoadByUniqueKey(String propertyName, Object uniqueKey, ISessionImplementor session) c:\opt\nhibernate\2.1.2\source\src\NHibernate\Type\EntityType.cs(552,0): at NHibernate.Type.EntityType.LoadByUniqueKey(String entityName, String uniqueKeyPropertyName, Object key, ISessionImplementor session) I'm using NHibernate 2.1.2 and I've been debugging into the NHibernate source, but I'm coming up empty. Any suggestions? Thanks so much!

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• UIScrollView. Any thoughts on implementing "infinite" scroll/zoom?

  - by dugla

  So, UITableView supports essentially "infinite" scrolling. There' may be a limit but that sucker can scroll for a looonnnggg time. I would like to mimic this behavior with a UIScrollView but there are two fundamental impediments: 1) scrollView.contentSize is fixed at creation time. 2) zooming can blow any lazy-loading scheme all to hell since it can cause infinte data explosion. Have others out there pondered this idea? Yah, I know, we are essentially talking about re-creating Google Maps here. Any insights would be much appreciated. Cheers, Doug

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• jQuery to add vertical scroll bar for a fixed height div container

  - by Michael Mao

  Hi all: This is uni homework so sorry about :my password protected url Please enter usersame as "uts" and password as "10479475", without the wrapper quotes. It it almost completed, please follow simple steps to see where my problem dwells: step1: click on any continent highlighted on world map; step2: click on any city marked on continent map; step3: enter quantity ranging from 1 to 6 into the upper-right table; step4 : there you go, in the table below, once row is equal or greater than 3, then the size of table starts to "overlap" on top of the footer section and continues to grow, which is not what I want. I want to achieve the effect that the table size has a limited max-height, so once actual height exceeds the threshold, then I can have a vertical scroll bar so to "stack up" my table and not to break the overall structure. It turns out that my lazy initial design now gets myself stuck in a problem... Any suggestion and hint on how to get this?

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• Mavericks system Ruby and gem broken

  - by T1000

  When I tried to run ruby -v or gem -v (or any other command), I get: dyld: lazy symbol binding failed: Symbol not found: _ruby_run Referenced from: /usr/local/bin/ruby Expected in: /usr/lib/libruby.dylib dyld: Symbol not found: _ruby_run Referenced from: /usr/local/bin/ruby Expected in: /usr/lib/libruby.dylib This is after I ran rvm system to temporally switch to the system default Ruby. RVM is working fine, but I have a special need to install a gem to the system Ruby and I can't because of this problem. Does anyone know why? It seems to be some kind of link problem to Ruby, but I'm don't know how to solve this. I ran which ruby and it's at this point located in "/usr/local/bin/ruby". I checked the Ruby in "/usr/lib/" and it's pointing to my system Ruby: "../../System/Library/Frameworks/Ruby.framework/Versions/Current/usr/lib/ruby" Any help would be appreciated.

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