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  • Understanding and Benefiting from Code Contracts in .NET 4.0

    One of the fundamental programming challenges is managing state. Chances are you have written dozens and dozens of methods that at the beginning check that certain conditions are met, and that another set of conditions is met when the method returns. With Code Contracts in .NET 4.0, you can make things considerably easier. Read on to learn how.

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  • Need help understanding a recursion example in Python

    - by Ali Mustafa
    Python is my first programming language, and I'm learning it from "How to Think Like a Computer Scientist". In Chapter 5 the author gives the following example on recursion: def factorial(n): if n == 0: return 1 else: recurse = factorial(n-1) result = n * recurse return result I understand that if n = 3, then the function will execute the second branch. But what I don't understand is what happens when the function enters the second branch. Can someone explain it to me?

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  • Adventures in Windows 8: Understanding and debugging design time data in Expression Blend

    - by Laurent Bugnion
    One of my favorite features in Expression Blend is the ability to attach a Visual Studio debugger to Blend. First let’s start by answering the question: why exactly do you want to do that? Note: If you are familiar with the creation and usage of design time data, feel free to scroll down to the paragraph titled “When design time data fails”. Creating design time data for your app When a designer works on an app, he needs to see something to design. For “static” UI such as buttons, backgrounds, etc, the user interface elements are going to show up in Blend just fine. If however the data is fetched dynamically from a service (web, database, etc) or created dynamically, most probably Blend is going to show just an empty element. The classical way to design at that stage is to run the application, navigate to the screen that is under construction (which can involve delays, need to log in, etc…), to measure what is on the screen (colors, margins, width and height, etc) using various tools, going back to Blend, editing the properties of the elements, running again, etc. Obviously this is not ideal. The solution is to create design time data. For more information about the creation of design time data by mocking services, you can refer to two talks of mine “Deep dive MVVM” and “MVVM Applied From Silverlight to Windows Phone to Windows 8”. The source code for these talks is here and here. Design time data in MVVM Light One of the main reasons why I developed MVVM Light is to facilitate the creation of design time data. To illustrate this, let’s create a new MVVM Light application in Visual Studio. Install MVVM Light from here: http://mvvmlight.codeplex.com (use the MSI in the Download section). After installing, make sure to read the Readme that opens up in your favorite browser, you will need one more step to install the Project Templates. Start Visual Studio 2012. Create a new MvvmLight (Win8) app. Run the application. You will see a string showing “Welcome to MVVM Light”. In the Solution explorer, right click on MainPage.xaml and select Open in Blend. Now you should see “Welcome to MVVM Light [Design]” What happens here is that Expression Blend runs different code at design time than the application runs at runtime. To do this, we use design-time detection (as explained in a previous article) and use that information to initialize a different data service at design time. To understand this better, open the ViewModelLocator.cs file in the ViewModel folder and see how the DesignDataService is used at design time, while the DataService is used at runtime. In a real-life applicationm, DataService would be used to connect to a web service, for instance. When design time data fails Sometimes however, the creation of design time data fails. It can be very difficult to understand exactly what is happening. Expression Blend is not giving a lot of information about what happened. Thankfully, we can use a trick: Attaching a debugger to Expression Blend and debug the design time code. In WPF and Silverlight (including Windows Phone 7), you could simply attach the debugger to Blend.exe (using the “Managed (v4.5, v4.0) code” option even for Silverlight!!) In Windows 8 however, things are just a bit different. This is because the designer that renders the actual representation of the Windows 8 app runs in its own process. Let’s illustrate that: Open the file DesignDataService in the Design folder. Modify the GetData method to look like this: public void GetData(Action<DataItem, Exception> callback) { throw new Exception(); // Use this to create design time data var item = new DataItem("Welcome to MVVM Light [design]"); callback(item, null); } Go to Blend and build the application. The build succeeds, but now the page is empty. The creation of the design time data failed, but we don’t get a warning message. We need to investigate what’s wrong. Close MainPage.xaml Go to Visual Studio and select the menu Debug, Attach to Process. Update: Make sure that you select “Managed (v4.5, v4.0) code” in the “Attach to” field. Find the process named XDesProc.exe. You should have at least two, one for the Visual Studio 2012 designer surface, and one for Expression Blend. Unfortunately in this screen it is not obvious which is which. Let’s find out in the Task Manager. Press Ctrl-Alt-Del and select Task Manager Go to the Details tab and sort the processes by name. Find the one that says “Blend for Microsoft Visual Studio 2012 XAML UI Designer” and write down the process ID. Go back to the Attach to Process dialog in Visual Studio. sort the processes by ID and attach the debugger to the correct instance of XDesProc.exe. Open the MainViewModel (in the ViewModel folder) Place a breakpoint on the first line of the MainViewModel constructor. Go to Blend and open the MainPage.xaml again. At this point, the debugger breaks in Visual Studio and you can execute your code step by step. Simply step inside the dataservice call, and find the exception that you had placed there. Visual Studio gives you additional information which helps you to solve the issue. More info and Conclusion I want to thank the amazing people on the Expression Blend team for being very fast in guiding me in that matter and encouraging me to blog about it. More information about the XDesProc.exe process can be found here. I had to work on a Windows 8 app for a few days without design time data because of an Exception thrown somewhere in the code, and it was really painful. With the debugger, finding the issue was a simple matter of stepping into the code until it threw the exception.   Laurent Bugnion (GalaSoft) Subscribe | Twitter | Facebook | Flickr | LinkedIn

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  • The understanding of flight search engine

    - by Jens Jensen
    Today I just discovered a search engine website who offered a service to enter your departure destination, and then search for which possible destinations you can have for the cheapest price. This is very nice to use, if one wants to flight somewhere but doesn't know which "good deals" are available. This is the site: http://www.kayak.com/explore/ Can someone explain to me, which programs are (mostly) used, and summarize how to make this sort of search engine. I think this is very interesting but unfortunately there are not shown all the possible flight tickets and therefore I think this project could be improved.

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  • Need help understanding XNA 4.0 BoundingBox vs BoundingSphere Intersection

    - by nerdherd
    I am new to both game programming and XNA, so I apologize if I'm missing a simple concept or something. I have created a simple 3D game with a player and a crate and I'm working on getting my collision detection working properly. Right now I am using a BoundingSphere for my player, and a BoundingBox for the crate. For some reason, XNA only detects a collision when my player's sphere touches the front face of the crate. I'm rendering all the BoundingSpheres and BoundingBoxes as wire frames so I can see what's going on, and everything visually appears to be correct, but I can't figure out this behavior. I have tried these checks: playerSphere.Intersects(crate.getBoundingBox()) playerSphere.Contains(crate.getBoundingBox(), ContainmentType.Intersects) playerSphere.Contains(crate.getBoundingBox()) != ContainmentType.Disjoint But they all seem to produce the same behavior (in other words, they are only true when I hit the front face of the crate). The interesting thing is that when I use a BoundingSphere for my crate the collision is detected as I would expect, but of course this makes the edges less accurate. Any thoughts or ideas? Have I missed something about how BoundingSpheres and BoundingBoxes compute their intersections? I'd be happy to post more code or screenshots to clarify if needed. Thanks!

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  • Understanding branching strategy/workflow correctly

    - by burnersk
    I'm using svn without branches (trunk-only) for a very long time at my workplace. I had discovered most or all of the issues related to projects which do not have any branching strategy. Unlikely this is not going to change at my workplace but for my private projects. For my private projects which most includes coworkers and working together at the same time on different features I like to have an robust branching strategy with supports long-term releases powered by git. I find out that the Atlassian Toolchain (JIRA, Stash and Bamboo) helped me most and it also recommending me an branching strategy which I like to verify for the team needs. The branching strategy was taken directly from Atlassian Stash recommendation with a small modification to the hotfix branch tree. All hotfixes should also merged into mainline. The branching strategy in words mainline (also known as master with git or trunk with svn) contains the "state of the art" developing release. Everything here was successfully checked with various automated tests (through Bamboo) and looks like everything is working. It is not proven as working because of possible missing tests. It is ready to use but not recommended for production. feature covers all new features which are not completely finished. Once a feature is finished it will be merged into mainline. Sample branch: feature/ISSUE-2-A-nice-Feature bugfix fixes non-critical bugs which can wait for the next normal release. Sample branch: bugfix/ISSUE-1-Some-typos production owns the latest release. hotfix fixes critical bugs which have to be release urgent to mainline, production and all affected long-term *release*es. Sample branch: hotfix/ISSUE-3-Check-your-math release is for long-term maintenance. Sample branches: release/1.0, release/1.1 release/1.0-rc1 I am not an expert so please provide me feedback. Which problems might appear? Which parts are missing or slowing down the productivity?

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  • SL150 Modular Tape Library Demo Equipment Purchase Opportunity Limited Special Pricing on Demo Configuration

    - by Cinzia Mascanzoni
    Oracle is pleased to announce that, for a limited time, Oracle VADs may purchase special SL150 Modular Tape Library configurations for demonstration purposes at a significantly reduced price. Submit your order today for these special SL150 Modular Tape Library configurations and you can start showcasing these products in partner demonstrations and proof-of-concepts. VADs may also sell demo units to their VARs so that they may use them in their customer evaluations to help shorten the sales cycle. The offer also allows VARs to sell the demo configuration after a prescribed demonstration period to support the demo product’s cost of ownership. Why wait? Order today! Rules and Guidelines Only authorized VADs are allowed to purchase the special SL150 Modular Tape Library configurations. Purchase time frame is from now until February 28, 2013. Only the predetermined configurations are approved for purchase at the prescribed discounts. Supply is allocated per region and it’s limited. Order MUST be placed via the Oracle Partner Store* (OPS) where applicable. See below for online and offline order processes. If reselling to a VAR, VAD must include the Partner Demonstration Hardware Terms with the order (online via OPS or with offline VAD Ordering Document). Please mark your calendars for the SL150 Modular Tape Library Demo Program webcast on Sept 5th. The objective of this call is to share the details of this demo program with you. For details on how to connect to the webcast, contact your VAD Manager

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  • Understanding hand written lexers

    - by Cole Johnson
    I am going to make a compiler for C (C99; I own the standards PDF), written in C (go figure) and looking up on how compilers work on Wikipedia has told me a lot. However, after reading up on lexers has confused me. The Wikipedia page states that: the GNU Compiler Collection (gcc) uses hand-written lexers I have tried googling what a hand written lexer and have come up with nothing except for "making a flowchart that describes how it should function", however, isn't that how all software development should be done? So my question is: "What is a hand written lexer?"

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  • Issue in understanding how to compare performance of classifier using ROC

    - by user1214586
    I am trying to demystify pattern recognition techniques and understood few of them. I am trying to design a classifier M. A gesture is classified based on the hamming distance between the sample time series y and the training time series x. The result of the classifier are probabilistic values. There are 3 classes/categories with labels A,B,C which classifies hand gestures where there are 100 samples for each class which are to be classified (single feature and data length=100). The data are different time series (x coordinate vs time). The training set is used to assign probabilities indicating which gesture has occured how many times. So,out of 10 training samples if gesture A appeared 6 times then probability that a gesture falls under category A is P(A)=0.6 similarly P(B)=0.3 and P(C)=0.1 Now, I am trying to compare the performance of this classifier with Bayes classifier, K-NN, Principal component analysis (PCA) and Neural Network. On what basis,parameter and method should I do it if I consider ROC or cross validate since the features for my classifier are the probabilistic values for the ROC plot hence what shall be the features for k-nn,bayes classification and PCA? Is there a code for it which will be useful. What should be the value of k is there are 3 classes of gestures? Please help. I am in a fix.

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  • Understanding Visitor Pattern

    - by Nezreli
    I have a hierarchy of classes that represents GUI controls. Something like this: Control-ContainerControl-Form I have to implement a series of algoritms that work with objects doing various stuff and I'm thinking that Visitor pattern would be the cleanest solution. Let take for example an algorithm which creates a Xml representaion of a hierarchy of objects. Using 'classic' approach I would do this: public abstract class Control { public virtual XmlElement ToXML(XmlDocument document) { XmlElement xml = document.CreateElement(this.GetType().Name); // Create element, fill it with attributes declared with control return xml; } } public abstract class ContainerControl : Control { public override XmlElement ToXML(XmlDocument document) { XmlElement xml = base.ToXML(document); // Use forech to fill XmlElement with child XmlElements return xml; } } public class Form : ContainerControl { public override XmlElement ToXML(XmlDocument document) { XmlElement xml = base.ToXML(document); // Fill remaining elements declared in Form class return xml; } } But I'm not sure how to do this with visitor pattern. This is the basic implementation: public class ToXmlVisitor : IVisitor { public void Visit(Form form) { } } Since even the abstract classes help with implementation I'm not sure how to do that properly in ToXmlVisitor. Perhaps there is a better solution to this problem. The reason that I'm considering Visitor pattern is that some algorithms will need references not available in project where the classes are implemented and there is a number of different algorithms so I'm avoiding large classes. Any thoughts are welcome.

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  • Understanding Photography Lighting with a Single Egg [Video]

    - by Jason Fitzpatrick
    In this informative video, veteran photographer Joe Edelman demonstrates the basics of photography lighting with a humble egg. An egg is an excellent shape for experimenting with and studying lighting because the curved surfaces provide a nice clean gradient to study how the light wraps and falls as you move around the light source. Check out the video above to see Edelman’s full demonstration of the humble egg as a photography teaching tool. [via DIY Photography] The Best Free Portable Apps for Your Flash Drive Toolkit How to Own Your Own Website (Even If You Can’t Build One) Pt 3 How to Sync Your Media Across Your Entire House with XBMC

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  • SQL SERVER Understanding ALTER INDEX ALL REBUILD with Disabled Clustered Index

    This blog is in response to the ongoing communication with the reader who had earlier asked the question of SQL SERVER Disable Clustered Index and Data Insert. The same reader has asked me the difference between ALTER INDEX ALL REBUILD and ALTER INDEX REBUILD along with disabled clustered index. Instead of writing a big [...]...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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  • Understanding CTR in Google Webmaster Tools

    - by sam
    I've got a site that's showing a 9% CTR for a phrase in Google Webmaster Tools, but the average position for my site is 14th (this includes 7 local results for this phrase). I was a little confused as to what the CTR actually meant, is it : for each person who searches for that phrase 9% of them click my site. or for each person who actually sees my site in the search results 9% of them click through (bearing in mind 14th is high on page 2 when the local listings are used).

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  • Understanding Key Factors For Corporate Logo Design

    You need to bind to certain basic principles that ensure that corporate logo design is professional and easy to remember and creates a great impact on viewers while successfully expressing the nature... [Author: Alan Smith - Web Design and Development - March 20, 2010]

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  • Understanding the SQL Server 2012 BI Semantic Model (BISM)

    SQL Server 2012 introduced an unified BI Semantic Model (BISM) which is based on some of the existing as well as some new technologies. This model is intended to serve as one model for all end user experiences for reporting, analytics, scorecards, dashboards, etc. In this tip, I will talk in detail about the new BISM, how it differs from earlier the earlier Unified Dimensional Model (UDM) and how BISM lays down a foundation for future.

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  • Understanding the Java Ecosystem

    - by syrion
    I have traditionally had the "luxury" of being a one-man development team. I've used Python extensively, have a reasonable command of Perl, PHP, and JavaScript. My problem is Java. I can write Java code. I'm not great at it--unlike Python, I rarely make use of anything unique to Java when I'm writing it. Furthermore, my experience is mostly in simple GUI/console programming. Unfortunately, I'm currently pursuing an IT degree where Java is the lingua franca. My database class is requiring that our projects be written in Java using servlets, and I just can't wrap my head around the ecosystem. Is there a good online overview of or tutorial on how the Java web ecosystem works? I have Thinking in Java, but it's mostly just the language itself (which I understand well enough to get by). I have looked at the Sun servlet tutorial, but it seems outdated.

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  • Understanding how to create/use textures for games when limited by power of two sizes

    - by Matthias Reisner
    I have some questions about the creating graphics for a game. As an example. I want to create a motorbike. (1pixel = 1centimeter) So my motorbike will have 200 width and 150 height. (200x150) But the libgdx only allows to load sizes with the power of 2?! (2,4,8,16,...) First I thought about that way. I will create my bike with the size (200x150) and save it as png. Than I will open it again (e.g. with gimp) resize the image to a size which uses values with power of 2 (128x128). I will load that as texture in the programm and set width as 200 and height as 150. But wouldn't it be a problem? Because I will lose some pixel information when I make the first conversation.?! Isn't it?

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  • Any enlightenment for understanding Object Oriented Programming? [closed]

    - by ????
    I studied computer science near the end of 1980s, and wasn't taught OOP that formally. With Pascal or C, when I understand the top-down design of functions, and the idea of black box, then everything just seem to make sense, as if there is a "oh I get it!" -- some kind of totally getting it and enlightenment feeling. But with OOP, all I know was the mechanics: the class, instance, method, inheritance, polymorphism, encapsulation. It was like, I knew all the "this is how it is", but never had the feeling of "I totally get it", the enlightened feeling. Would somebody be able to describe it, or point to a chapter in some book or paper which talks about OOP so that the reader can feel: "I totally get it!" on OOP?

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  • Understanding Service Compensation part of Industrial SOA series

    - by JuergenKress
    Some of the most important SOA design patterns that we have successfully applied in projects will be described in this article. These include the Compensation pattern and the UI mediator pattern, the Common Data Format pattern and the Data Access pattern. All of these patterns are included in Thomas Erl's book, "SOA Design Patterns", and are presented here in detail, together with our practical experiences. We begin our "best of" SOA pattern collection with the Compensation pattern. Compensation is required in error situations in an SOA, as multiple atomic service operations cannot generally be linked with classic transactions this would violate the principle of loose coupling. An error situation of this sort will occur, particularly if service operations are combined into processes or new services during orchestration or by applying the Composite pattern, and the transaction bracket has to be expanded as a result. We need mechanisms to undo the effects of individual services (the status changes in the overall system) and to ensure that a consistent system state is maintained at all times, so as to preserve system integrity. For the Compensation pattern, we would like to address the following questions: Why is compensation important in relation to SOA? How is the topic of compensation linked with the topic of transactions? What are the challenges with regard to compensation... Read the full article in the Service Technology Magazine or at OTN. Share your comments and feedback on the Industrial SOA series by using the hashtag #industrialsoa. Missed an article of the Industrial SOA series visit the overview at OTN. SOA & BPM Partner Community For regular information on Oracle SOA Suite become a member in the SOA & BPM Partner Community for registration please visit www.oracle.com/goto/emea/soa (OPN account required) If you need support with your account please contact the Oracle Partner Business Center. Blog Twitter LinkedIn Facebook Wiki Mix Forum Technorati Tags: Industrial SOA,SOA,SOA Service Compensation,Community,Oracle SOA,Oracle BPM,OPN,Jürgen Kress

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