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• How does NSValue do its magic?

  - by Paperflyer

  I have an MVC application. The model has a property that is a struct NSSize. It is writable like this: - (void)setSize:(NSSize)aSize; The view sets this NSSize using key-value-coding. However, you can not key-value-code a struct, so I wrapped it in an NSValue-object like this: [theView setValue:[NSValue valueWithSize:mySize] forKey:@"theModel.size"]; To my understanding, this should not work since the accessor expects a struct and not an NSValue. But it works perfectly. Magically. How is this possible?

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• How to enable ajax when deriving from System.Web.UI.WebControls.WebControl on controls that are crea

  - by Dave

  I've built a class that derives from System.Web.UI.WebControl. It basically renders pagination links (same as what you see on top of GridView when enabled) for use above a repeater. I'm creating some anchor tags explicitly inside my nav control obviously, but they don't perform ajax postbacks. My understanding is that ajax requires POSTS to work right? Well, these would be GETs which I think is the problem. Is there a way to achieve what I'm trying to do? Thanks!

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• SqlParameter contructor compiler overload choice

  - by Ash

  When creating a SqlParameter (.NET3.5) or OdbcParameter I often use the SqlParameter(string parameterName, Object value) constructor overload to set the value in one statement. When I tried passing a literal 0 as the value paramter I was initially caught by the C# compiler choosing the (string, OdbcType) overload instead of (string, Object). MSDN actually warns about this gotcha in the remarks section, but the explanation confuses me. Why does the C# compiler decide that a literal 0 parameter should be converted to OdbcType rather than Object? The warning also says to use Convert.ToInt32(0) to force the Object overload to be used. It confusingly says that this converts the 0 to an "Object type". But isn't 0 already an "Object type"? The Types of Literal Values section of this page seems to say literals are always typed and so inherit from System.Object. This behavior doesn't seem very intuitive given my current understanding? Is this something to do with Contra-variance or Co-variance maybe?

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• Why isn't wchar_t widely used in code for Linux / related platforms?

  - by Ninefingers

  This intrigues me, so I'm going to ask - for what reason is wchar_t not used so widely on Linux/Linux-like systems as it is on Windows? Specifically, the Windows API uses wchar_t internally whereas I believe Linux does not and this is reflected in a number of open source packages using char types. My understanding is that given a character c which requires multiple bytes to represent it, then in a char[] form c is split over several parts of char* whereas it forms a single unit in wchar_t[]. Is it not easier, then, to use wchar_t always? Have I missed a technical reason that negates this difference? Or is it just an adoption problem?

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• What is going on with the "return fibonacci( number-1 ) + fibonacci( number-2 )"?

  - by user1478598

  I have problem understanding what the return fibonacci( number-1 ) + fibonacci( number-2 ) does in the following program: import sys def fibonacci( number ): if( number <= 2 ): return 1 else: return fibonacci( number-1 ) + fibonacci( number-2 ) The problem is that I can't imagine how this line works: return fibonacci( number-1 ) + fibonacci( number-2 ) Does the both of the "fibonacci( number-1 )" and "fibonacci( number-2 )" being processed at the same time? or the "fibonacci( number-1 )" is the first to be processed and then the second one? I only see that processing both of them would eventually return '1' so the last result I expect to see it is a '1 + 1' = '2' I would appreciate a lot, If someone can elaborately explain the process of its calculation. I think this is a very newb question but I can't really get a picture of its process.

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• What to pass to UserType, BlobType.setPreparedStatement session parameter

  - by dlots

  http://blog.xebia.com/2009/11/09/understanding-and-writing-hibernate-user-types/ I am attempting to defined a customer serialization UserType that mimics, the XStreamUserType referenced and provided here: http://code.google.com/p/aphillips/source/browse/commons-hibernate-usertype/trunk/src/main/java/com/qrmedia/commons/persistence/hibernate/usertype/XStreamableUserType.java My serializer outputs a bytearray that should presumably written to a Blob. I was going to do: public class CustomSerUserType extends DirtyCheckableUserType { protected SerA ser=F.g(SerA.class); public Class<Object> returnedClass() { return Object.class; } public int[] sqlTypes() { return new int[] {Types.BLOB}; } public Object nullSafeGet(ResultSet resultSet,String[] names,Object owner) throws HibernateException,SQLException { if() } public void nullSafeSet(PreparedStatement preparedStatement,Object value,int index) throws HibernateException,SQLException { BlobType.nullSafeSet(preparedStatement,ser.ser(value),index); } } Unfortunetly, the BlobType.nullSafeSet method requires the session. So how does one define a UserType that gets access to a servlet requests session? EDIT: There is a discussion of the issue here and it doesn't appear there is a solution: Best way to implement a Hibernate UserType after deprecations?

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• Determining the magnitude of a certain frequency on the iPhone

  - by eagle

  I'm wondering what's the easiest/best way to determine the magnitude of a given frequency in a sound. It's my understanding that a FFT function will return the magnitudes of all frequencies in a signal. I'm wondering if there is any shortcut I could use if I'm only concerned about a specific frequency. I'll be using the iPhone mic to record the audio. My guess is that I'll be using the Audio Queue Services for recording since I don't need to record the audio to a file. I'm using SDK 4.0, so I can use any of the functions defined in the Accelerate framework (e.g. FFT functions) if needed. Update: I updated the question to be more clear as per Conrad's suggestion.

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• jQuery Plugin Overwriting Parameters

  - by Travis

  Hey Everyone, This maybe a very mundane question, but this is the first jQuery plugin that I write and I'm a bit fuzzy on understanding the scope rules in Javascript. I'm trying to write an simple jQuery plugin that wraps around the Stack Overflow API. I'm starting off by trying to work with the Flair API. I wanted to make the plugin as configurable as possible so that you can easily pass it the domain and user id, and generate multiple Flairs. var superUser = $.jStackOverflow.flair({domain:"superuser.com", id: 30162, parentId:'#su-flair'}); var stackOverflow = $.jStackOverflow.flair({domain:"stackoverflow.com", id: 55954, parentId:'#so-flair'}); The problem is, when it makes the second call, its somehow using the correct domain and id parameters, but the parentId field that it's using in the callback function to create the html, is using the first parameter. You can see the plugin here and the html here

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• Storing UTF-8 XML using Word's CustomXMLPart or any other supported way

  - by wpfwannabe

  I am writing a Word add-in which is supposed to store some own XML data per document using Word object model and its CustomXMLPart. The problem I am now facing is the lack of IStream-like functionality for reading/writing XML to/from a CustomXMLPart. It only provides BSTR interface and I am puzzled how to handle UTF-8 XMLs with BSTRs. To my understanding an UTF-8 XML file should really never have to undergo this sort of Unicode conversion. I am not sure what to expect as a result here. Is there another way of using Word automation interfaces to store arbitrary custom information inside a DOCX file?

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• Strange thing about .NET 4.0 filesystem enumeration functionality

  - by codymanix

  I just read a page of "Whats new .NET Framework 4.0". I have trouble understanding the last paragraph: To remove open handles on enumerated directories or files Create a custom method (or function in Visual Basic) to contain your enumeration code. Apply the MethodImplAttribute attribute with the NoInlining option to the new method. For example: [MethodImplAttribute(MethodImplOptions.NoInlining)] Private void Enumerate() Include the following method calls, to run after your enumeration code: * The GC.Collect() method (no parameters). * The GC.WaitForPendingFinalizers() method. Why the attribute NoInlining? What harm would inlining do here? Why call the garbage collector manually, why not making the enumerator implement IDisposable in the first place? I suspect they use FindFirstFile()/FindNextFile() API calls for the imlementation, so FindClose() has to be called in any case if the enumeration is done.

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• Use anchor to display div

  - by scatteredbomb

  I'm using jquery, and need to accomplish a couple things. 1) When someone clicks on a link (or in my case, a div) to display another div, I'd like to add an anchor to the url. So, if someone clicks on a "Live" link, the 'live' div slides down, and we append #live to the url. 2) If someone visits that page and keeps the #live anchor at the end of the url, then the 'live' div should be visible right away. I know how to handle the basic part of slideDown() if someone clicks a div. I don't know how to append the hashtag, or make it so that when the page is loaded that hashtag is checked and displays the respective div. Any help understanding this would be appreciated. Thanks in advance.

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• What design pattern do you use the most?

  - by spoon16

  I'm interested in understanding what design patterns people find themselves using often. Hopefully this list will help other recognize common scenarios and the associated design pattern that can be used to solve them. Please describe a common problem you find yourself solving and the design pattern(s) you use to solve it. Links to blogs or documentation describing the pattern are also appreciated. Edit: Please expand on your answers a bit, I would like this to be a useful reference for someone who wants to learn more about design patterns and is curious on what situations a specific design pattern might be used. Nobody has linked to any "more learning" resources.

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• Unreachable code detected by using const variables

  - by Anton Roth

  I have following code: private const FlyCapture2Managed.PixelFormat f7PF = FlyCapture2Managed.PixelFormat.PixelFormatMono16; public PGRCamera(ExamForm input, bool red, int flags, int drawWidth, int drawHeight) { if (f7PF == FlyCapture2Managed.PixelFormat.PixelFormatMono8) { bpp = 8; // unreachable warning } else if (f7PF == FlyCapture2Managed.PixelFormat.PixelFormatMono16){ bpp = 16; } else { MessageBox.Show("Camera misconfigured"); // unreachable warning } } I understand that this code is unreachable, but I don't want that message to appear, since it's a configuration on compilation which just needs a change in the constant to test different settings, and the bits per pixel (bpp) change depending on the pixel format. Is there a good way to have just one variable being constant, deriving the other from it, but not resulting in an unreachable code warning? Note that I need both values, on start of the camera it needs to be configured to the proper Pixel Format, and my image understanding code needs to know how many bits the image is in. So, is there a good workaround, or do I just live with this warning?

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• NoSql Crash Course/Tutorial

  - by Chris Thompson

  Hi all, I've seen NoSQL pop up quite a bit on SO and I have a solid understanding of why you would use it (from here, Wikipedia, etc). This could be due to the lack of concrete and uniform definition of what it is (more of a paradigm than concrete implementation), but I'm struggling to wrap my head around how I would go about designing a system that would use it or how I would implement it in my system. I'm really stuck in a relational-db mindset thinking of things in terms of tables and joins... At any rate, does anybody know of a crash course/tutorial on a system that would use it (kind of a "hello world" for a NoSQL-based system) or a tutorial that takes an existing "Hello World" app based on SQL and converts it to NoSQL (not necessarily in code, but just a high-level explanation). I see this having one solid answer, but if you guys feel like it should be community wiki, I'll be happy to change it. Thanks! Chris

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• How can I learn the math necessary for working with computer vision?

  - by Duncan Benoit

  I know that computer vision involves a lot of math, but I need some tips about how programmers gain that knowledge. I've started to use the OpenCV library but I have some major problems in understanding how the math works in the algorithms. In college I have studied some math and we worked with matrices and derivatives, but I didn't pay to much attention to the subject. It seemed to be so difficult and useless from a programmer point of view. I suppose that there has to be some easy way to understand what a second derivative is without calculating an equation. (Derivatives are just an example) Do you have any tips for me about how can i gain such knowledge? A forum, book, link, advice, anything?

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• Do I correctly understand what a class is?

  - by Matt

  I've had trouble finding a clear, concise laymans definition of a class. Usually, they give general ideas without specifically spelling it out, and I'm wondering if I'm understanding this correctly. As I understand it, a class is the set of code that controls an object. For example, in an app that has a button for 'Yes' and a button for 'No', and a text box for output, the code that tells the computer what to do when the user uses the Yes button is one class, the code for hitting No is another class, and an object is the two buttons and what they do together to influence the output box. Am I right, or am I confusing terms here? Thanks

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• how to feed a file to telnet

  - by knittl

  hello community, understanding http and headers i played around with telnet to send requests. to not type everything again and again and again i thought i'd write a small textfile with all the commands i need. my file is as simple as follows: GET /somefile.php HTTP/1.1 Host: localhost i then try to feed it to telnet with io-redirection: $ telnet localhost 80 < telnet.txt but all output i get is Trying ::1... Connected to localhost. Escape character is '^]'. Connection closed by foreign host. what am i doing wrong?

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• how can I implement Comparable more than once?

  - by codeman73

  I'm upgrading some code to Java 5 and am clearly not understanding something with Generics. I have other classes which implement Comparable once, which I've been able to implement. But now I've got a class which, due to inheritance, ends up trying to implement Comparable for 2 types. Here's my situation: I've got the following classes/interfaces: interface Foo extends Comparable<Foo> interface Bar extends Comparable<Bar> abstract class BarDescription implements Bar class FooBar extends BarDescription implements Foo With this, I get the error 'interface Comparable cannot be implemented more than once with different arguments...' Why can't I have a compareTo(Foo foo) implemented in FooBar, and also a compareTo(Bar) implemented in BarDescription? Isn't this simply method overloading?

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• Visual Studio Editor, MEF in-Depth

  - by NewProgrammer

  I have been having difficulty simply writing a Visual Studio Editor Extension with MEF (Managed Extensiblity Framework). I thank those who answered my previous question, as they helped me know that I need to work with MEF. I've been trying to learn MEF for the Visual Studio Editor from MSDN's page, Extending the Editor, but it appears that I have a hard time understanding it. Can anyone provide strong resource or tutorials in addressing problem such as using the right ContentTypeDefintion (IGlyphFactory, TextMarkTag, etc...), and what is a ITagger. I need to understand these things, as most of the walkthrough only extending the text, such as only using the "spans" functionality, while I need to use "selection" methods and use MouseEventHandlers. Does anyone know an example similiar to my example, or references can tell me something about MEF's for VS editor in-depth?

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• Admin section in CakePHP

  - by Nicklas Ansman

  I'm having a hard time understanding how the CakePHP admin system works. Should all controllers who has an action which requires login include AuthComponent or just the one who handles the login/logout? Let's say I want to protect the add action of a controller. First I create admin_add() in the controller and then in the beforeFilter() method I check if $this->Session->check('Auth.User') is set a redirect based on this? Turns out it was better to just controll this with $this->Auth->allow() What is the easiest way to return to the URL the user was trying to access? Is there a better way than setting a session variable? Turns out it does this automagically :) If someone has a good tutorial for this I would happily read it :) I've already read this tutorial but I found it to be a little to basic and the CakePHP-docs are not that great on this topic either.

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• Best way to save complex Python data structures across program sessions (pickle, json, xml, database

  - by Malcolm

  Looking for advice on the best technique for saving complex Python data structures across program sessions. Here's a list of techniques I've come up with so far: pickle/cpickle json jsonpickle xml database (like SQLite) Pickle is the easiest and fastest technique, but my understanding is that there is no guarantee that pickle output will work across various versions of Python 2.x/3.x or across 32 and 64 bit implementations of Python. Json only works for simple data structures. Jsonpickle seems to correct this AND seems to be written to work across different versions of Python. Serializing to XML or to a database is possible, but represents extra effort since we would have to do the serialization ourselves manually. Thank you, Malcolm

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• Learning resources for Linux filesystem, command line, and structure

  - by webworm

  Can anyone suggest some good materials for learning more about the Linux filesystem and command line? I have found myself frequently confused as to what programs go where on the Linux filesystem. I would like to learn how the various directories (var, etc, usr ...) are used and how to use the commandline more effectively. I come from the Windows development world (.NET developer) so I am very familiar with Windows system administration. However, when doing more and more work with PHP I found myself lost in the internals of Linux (specifically Ubuntu). For example I was having problems installing PEAR properly on my Ubuntu system and not understanding why it was installed where it was. All of my interactions with Linux machines is done via SSH so I would like to focus on the command line and the filesystem. Thanks for any suggestions.

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• Beginner question: What is binding?

  - by JDelage

  Hi, I was trying to understand the difference between early and late binding, and in the process realized that the concept of binding is nebulous to me. I think I understand that it relates to the way data-as-a-word-of-memory is linked to type-as-a-set-of-language-features but I am not sure those are the right concepts. Also, how does understanding this deeply help people become better programmers? Please note: This question is not "what is late v. early binding" or "what are the trade-offs between the 2". Those already exist here. Thanks, JDelage

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• const TypedeffedIntPointer not equal to const int *

  - by dirk

  I have the following C++ code: typedef int* IntPtr; const int* cip = new int; const IntPtr ctip4 = cip; I compile this with Visual Studio 2008 and get the following error: error C2440: 'initializing' : cannot convert from 'const int *' to 'const IntPtr' Clearly my understanding of typedefs is not what is should be. The reason I'm asking, I'm storing a pointer type in a STL map. I have a function that returns a const pointer which I would like to use to search in the map (using map::find(const key_type&). Since const MyType* and const map<MyType*, somedata>::key_type is incompatible, I'm having problems. Regards Dirk

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• I dont understand how Westpac Payway API and NET works

  - by spirytus

  Been googling all day, reading numerous pdf's and still getting confused with the concepts of sending data to Payway system from Westpac (bank in Australia, link text). They offer access via API but also give access via what they call NET. The way I understand is that when client want to pay on my website, in case of NET, client gets to the page (hosted by a bank or hosted by me) where is provided with form to enter credit card info details. Then this form is submitted via normal POST call to Payway's specific https address. It is processed then and browser returns to url I specified as one of the parameters I sent in hidden field. In case of API story is similar, so user receives form, fills in the data and then data is send to my backend (not Payway's). My backend then calls payway API with data provided and once answer received returns confirmation page to the client. Is my understanding right? Please explain as I have a feeling I am missing something basic here.

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