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  • C# Using singleton instead of a global static instance

    - by Farstucker
    I ran into a problem today and a friend recommended I use a global static instance or more elegantly a singleton pattern. I spent a few hours reading about singletons but a few things still escape me. Background: What Im trying to accomplish is creating an instance of an API and use this one instance in all my classes (as opposed to making a new connection, etc). There seems to be about 100 ways of creating a singleton but with some help from yoda I found some thread safe examples. ..so given the following code: public sealed class Singleton { public static Singleton Instance { get; private set; } static Singleton() { Instance = new Singleton(); } } How/Where would you instantiate the this new class and how should it be called from a separate class? Thanks for your help.

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  • Avoiding Nested Blocks

    - by Helium3
    If there is a view controller that wants to execute a number of block based tasks one at a time, how can the control be given back to the view controller after a completion block has executed. Lets say ViewControllerOne wants to execute a number of tasks, each relying on the result of the previous one, how would this control be given back to the viewcontroller after each completion block has been executed? I started thinking about this and I was heading towards a deeply nested block pattern that will surely only cause confusion to whoever else reads or tests it. A task executes and the completion block returns the result or error which is needed by the next task, which has its own completion task, that the next task relies on and so forth. How can the control be managed in one place, the viewcontroller? Would the completion block just call the next function that handles the next task, using a pointer to the view controller?

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  • Can this be done with single SQL query

    - by Ghostrider
    I'm using MySQL. I have a table Type SubType 1 1 1 5 1 6 1 8 2 2 2 3 3 1 3 2 3 3 For each type there is some number of subtypes. For every subtype in a type there is a corresponding subtype in the next type: (1,1) => (2,2) (1,5) => (2,3) (1,6) => (2,2) (1,8) => (2,3) (2,2) => (3,1) (2,3) => (3,2) In case you haven't seen the pattern, here it is: you sort both current and next types by subtype, then in the next type you get subtype in the same position as your current subtype in current type is. If there are more subtypes in the current type that in the next one, you warp around and start from the first subtype in the next type. Is it possible to construct a query that takes current type and subtype and returns corresponding subtype in the next type?

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  • How can I create a qr// in Perl 5.12 from C?

    - by kristina
    This has been working for me in 5.8 and 5.10, but in 5.12 my code creates this weird non-qr object: # running "print Dumper($regex)" $VAR1 = bless( do{\(my $o = '')}, 'Regexp' ); Whereas printing a qr// not created by my code looks like this: # running "print Dumper(qr/foo/i)" $VAR1 = qr/(?i-xsm:foo)/; My code is basically: REGEXP *rx = re_compile(pattern, flags); SV *regex = sv_2mortal(newSVpv("",0)); sv_magic(regex, (SV*)rx, PERL_MAGIC_qr, 0, 0); stash = gv_stashpv("Regexp", 0); sv_bless(newRV((SV*)regex), stash); Anyone know how to correctly create a regex from a string in 5.12?

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  • string parsing and substring in c

    - by Josh
    I'm trying to parse the string below in a good way so I can get the sub-string stringI-wantToGet: const char *str = "Hello \"FOO stringI-wantToGet BAR some other extra text"; str will vary in length but always same pattern - FOO and BAR What I had in mind was something like: const char *str = "Hello \"FOO stringI-wantToGet BAR some other extra text"; char *probe, *pointer; probe = str; while(probe != '\n'){ if(probe = strstr("\"FOO")!=NULL) probe++ else probe = ""; // Nulterm part if(pointer = strchr(probe, ' ')!=NULL) pointer = '\0'; // not sure here, I was planning to separate it with \0's } Any help will be appreciate it.

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  • Why implement DB connection pointer object as a reference counting pointer? (C++)

    - by DVK
    At our company one of the core C++ classes (Database connection pointer) is implemented as a reference counting pointer. To be clear, the objects are NOT DB connections themselves, but pointers to a DB connection object. The library is very old, and nobody who designed is around anymore. So far, nether I, nor any C++ experts in the company that I asked have come up with a good reason for why this particular design was chosen. Any ideas? It is introducing some problems (partially due to awful reference pointer implementation used), and I'm trying to understand if this design actually has some deep underlying reasons? The usage pattern these days seems to be that the DB connection pointer object is returned by a DB connection manager class, and it's somewhat unclear whether DB connection pointers were designed to be able to be used independently of DB connection manager.

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  • Customizing UISlider look

    - by tcurdt
    To customize the visual look of a UISlider you can set the thumb and track images. Part of the track images gets stretched to the appropriate with. From the documentation: A stretchable region sits between two end cap regions. The end caps define the portions of the image that remain as is and are not stretched. The stretchable region is a 1-point wide area between the end caps that can be replicated to make the image appear longer. Now the problem I have is that my stretchable region needs to be more than 1-point wide. (It's a pattern) Unfortunately the 1-point width seems to be hard coded in the SDK. Anyone having an idea how to work around this? Or will I have to write my own slider from scratch for this?

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  • how to open many files simultaneously for reading in c

    - by monkeyking
    I'm trying to port some of my c++ code into c. I have the following construct class reader{ private: FILE *fp; alot_of_data data;//updated by read_until() method public: reader(const char*filename) read_until(some conditional dependent on the contents of the file, and the arg supplied) } Im then instantiating hundreds of these object and iterate over them using several 'read_until()' for each file until allfiles is at eof. I'm failing to see any clever way to do this in c, the only solution I can come up with is making an array of FILE pointers, and do the same with all the private member data from my class. But this seems very messy, can I implement the functionality of my class as a function pointer, or anything better, I think I'm missing a fundamental design pattern? The files are way to big to have all in memory, so reading everything from every file is not feasible Thanks

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  • how to fetch a range of files from an FTP server using C#

    - by user260076
    hello all, i'm stuck at a point where i am using a wildcard parameter with the FtpWebRequest object as suck FtpWebRequest reqFTP = (FtpWebRequest)FtpWebRequest.Create(new Uri("ftp://" + ftpServerIP + "/" + WildCard)); now this works fine, however i now want to fetch a specific range of files. say the file naming structure is *YYYYMMDD.* and i need to fetch all the files prior to today's date. i've been searching for a wildcard pattern for that with no good results, one that will work in a simple file listing. and it doesn't look like i can use regex here. any thoughts ?

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  • Efficient storage/retrieval method for replayable comet style applications (Google Wave, Etherpad)

    - by Gareth Simpson
    I am considering a web application that would have the same kind of multi user, automatic saving, infinite undo / replay capabilities that you see in Google Wave and Etherpad (albeit on a drastically smaller scale and userbase). Before I go away and reinvent the wheel, is this something that has already been addressed as either a piece of technology or library, or even just a design pattern. I know this isn't necessarily the best Stack Overflow question as there is probably not a "right" answer, but my Google-fu has failed me and I'd just like a reading list! Ordinarily I would be developing under python/django but this is not a firm requirement just a preference :)

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  • Is it possible to listen to relational database update?

    - by Morgan Cheng
    Is it possible to listen to relation database update? For example, my web app want to send data update to client through Comet technology. I can have the program to poll the database periodically, but that would not be performant and scalable. If app can hood to a "event handler" of database, then app can get notification every time given database table data is updated. This sounds more promising, but I didn't find any concrete example for it. This is listener pattern. Does common relational database support such feature?

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  • htaccess Redirect - First Segment to PHP File, Second Segment as Parameter

    - by Steve
    My htaccess redirect knowledge is somewhat weak, so I was hoping to get some help here. I currently have the following redirect, which works well: # remove trailing slash RewriteRule ^(.*)/$ /$1 [L,R=301] # redirect to clean URL RewriteCond /%{REQUEST_FILENAME}.php -f RewriteRule ^([a-zA-Z0-9_-\s]+)$ /$1.php This takes a URL like www.mysite.com/about to www.mysite.com/about.php Now I would like to keep this behavior, but add parameters (if applicable), as such: www.mysite.com/about = www.mysite.com/about.php www.mysite.com/gallery/1 = www.mysite.com/gallery.php?id=1 If possible, I might like to expand this system to 2 or more parameters, as such: www.mysite.com/gallery/1/2 = www.mysite.com/gallery.php?id=1&section=2 So the pattern would be: First URL segment redirects to a PHP file (Optionally) the second segment gets added as the id parameter (Optionally) the third segment gets added as the section parameter

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  • Using polyfit to predict where the object falls ?

    - by ZaZu
    Hi there, I have information of an object being thrown at a parabolic pattern. There are 30 images in total taken at specific intervals from the start position till the end. Now I have managed to extract the x,y coordinates of the object being thrown in all 30 images... I think that using polyfit (or maybe polyval ? ) may help me predict where the object will fall after the first 15 images ... I just want to know, how can polyfit be used with the 30 x,y coordinates I have ? ( I have a loop to extract each image from a mat file 1 row at a time until 30 .. and then plot that image .. so should I use polyfit in the same loop before/after the plot ??? Any ideas ?? Thanks !

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  • Django "Page not found" error page shows only one of two expected urls

    - by Frank V
    I'm working with Django, admittedly for the first time doing anything real. The URL config looks like the following: urlpatterns = patterns('my_site.core_prototype.views', (r'^newpost/$', 'newPost'), (r'^$', 'NewPostAndDisplayList'), # capture nothing... #more here... - perhaps the perma-links? ) This is in an app's url.py which is loaded from the project's url.py via: urlpatterns = patterns('', # only app for now. (r'^$', include('my_site.core_prototype.urls')), ) The problem is, when I receive a 404 attempting to utilize newpost, the error page only shows the ^$ -- it seems to ignore the newpost pattern... I'm sure the solution is probably stupid-simple but right now I'm missing it. Can someone help get me on the right track...

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  • How to use a 3rd party control inside the viewmodel?

    - by Sander
    I have a 3rd party control which among other things performs loading of some data. I want my viewmodel to keep track of this load operation and adjust its own state accordingly. If it were up to me, I'd do the data loading far away from the view, but it is not. So, I seem to be in the situation where my viewmodel depends on my view. How do I best handle this? I feel rather dirty making the view publish events to the viewmodel but I don't see any other reasonable way to get this info into the viewmodel. A similar situation might crop up with standard controls, too - imagine if your viewmodel depends on the events coming from a MediaElement - how do you properly model this? Do you put the MediaElement into the viewmodel? That doesn't sound right. If publishing the events to the viewmodel is indeed the most reasonable way, is there some common pattern used for this? How do you do it?

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  • System.Timers.Timer leaking due to "direct delegate roots"

    - by alimbada
    Apologies for the rather verbose and long-winded post, but this problem's been perplexing me for a few weeks now so I'm posting as much information as I can in order to get this resolved quickly. We have a WPF UserControl which is being loaded by a 3rd party app. The 3rd party app is a presentation application which loads and unloads controls on a schedule defined by an XML file which is downloaded from a server. Our control, when it is loaded into the application makes a web request to a web service and uses the data from the response to display some information. We're using an MVVM architecture for the control. The entry point of the control is a method that is implementing an interface exposed by the main app and this is where the control's configuration is set up. This is also where I set the DataContext of our control to our MainViewModel. The MainViewModel has two other view models as properties and the main UserControl has two child controls. Depending on the data received from the web service, the main UserControl decides which child control to display, e.g. if there is a HTTP error or the data received is not valid, then display child control A, otherwise display child control B. As you'd expect, these two child controls bind two separate view models each of which is a property of MainViewModel. Now child control B (which is displayed when the data is valid) has a RefreshService property/field. RefreshService is an object that is responsible for updating the model in a number of ways and contains 4 System.Timers.Timers; a _modelRefreshTimer a _viewRefreshTimer a _pageSwitchTimer a _retryFeedRetrievalOnErrorTimer (this is only enabled when something goes wrong with retrieving data). I should mention at this point that there are two types of data; the first changes every minute, the second changes every few hours. The controls' configuration decides which type we are using/displaying. If data is of the first type then we update the model quite frequently (every 30 seconds) using the _modelRefreshTimer's events. If the data is of the second type then we update the model after a longer interval. However, the view still needs to be refreshed every 30 seconds as stale data needs to be removed from the view (hence the _viewRefreshTimer). The control also paginates the data so we can see more than we can fit on the display area. This works by breaking the data up into Lists and switching the CurrentPage (which is a List) property of the view model to the right List. This is done by handling the _pageSwitchTimer's Elapsed event. Now the problem My problem is that the control, when removed from the visual tree doesn't dispose of it's timers. This was first noticed when we started getting an unusually high number of requests on the web server end very soon after deploying this control and found that requests were being made at least once a second! We found that the timers were living on and not stopping hours after the control had been removed from view and that the more timers there were the more requests piled up at the web server. My first solution was to implement IDisposable for the RefreshService and do some clean up when the control's UnLoaded event was fired. Within the RefreshServices Dispose method I've set Enabled to false for all the timers, then used the Stop() method on all of them. I've then called Dispose() too and set them to null. None of this worked. After some reading around I found that event handlers may hold references to Timers and prevent them from being disposed and collected. After some more reading and researching I found that the best way around this was to use the Weak Event Pattern. Using this blog and this blog I've managed to work around the shortcomings in the Weak Event pattern. However, none of this solves the problem. Timers are still not being disabled or stopped (let alone disposed) and web requests are continuing to build up. Mem Profiler tells me that "This type has N instances that are directly rooted by a delegate. This can indicate the delegate has not been properly removed" (where N is the number of instances). As far as I can tell though, all listeners of the Elapsed event for the timers are being removed during the cleanup so I can't understand why the timers continue to run. Thanks for reading. Eagerly awaiting your suggestions/comments/solutions (if you got this far :-p)

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  • A PHP object server for business logic

    - by Matthieu
    I wonder if such a thing is possible or even exist : In the MVC pattern, I would like to have the Model part to be persistant in memory, instead of reloading my instances at each execution. So I want only the Controller and View part to be executed. Is there any solution of server that would provide PHP objects (just like a Mysql server provides data records), and that keeps these objects in memory ? A problem would be also : how to have a constructed query to get objects ? Maybe PHP Linq ?

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  • Zend Framework Custom Validation Class Error Message

    - by remlabm
    The validation fails as it should but does not return the error message. $form->addElement('text', 'phone_number', array( 'required' => true, 'validators' => array( array('NotEmpty', true, array('messages' => 'Enter a valid Phone Number')), array('regex', false, array('pattern' => '/\([0-9]{3}\)\s[0-9]{3}-[0-9]{4}/', 'messages' => 'Enter a valid Phone Number' )), 'CheckPhoneNumber'), ), )); Custom Class: class Custom_Validators_CheckPhoneNumber extends Zend_Validate_Abstract{ const IN_USE = 'inUse'; protected $_messageTemplates = array( self::IN_USE => "'%value%' is currently in use" ); public function isValid($value) { $this->_setValue($value); $user_check = Users::getActive(preg_replace("/[^0-9]/", "", $value)); if($user_check->id){ $this->_error(self::IN_USE); return false; } return true; } } Just fails does not give the "IN_USE" error.

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  • Favoriting system on Appengine

    - by Mateusz Cieslak
    Hi, I have the following model structure class Authors(db.Model) : nickname = db.StringProperty(required=True) fullname = db.StringProperty(required=True) class Articles(db.Model) : title = db.StringProperty(required=True) body = db.StringProperty(required=True) author = db.ReferenceProperty(Authors, required=True) class Favorites(db.Model) : who = db.ReferenceProperty(Authors, required=True) what = db.ReferenceProperty(Articles, required=True) I'd like to display 10 last articles according to this pattern: article.title, article.body, article.author(nickname), info if this article has been already favorited by the signed in user. I have added a function which I use to get the authors of these articles using only one query (it is described here) But I don't know what to do with the favorites (I'd like to know which of the displayed articles have been favorited by me using less than 10 queries (I want to display 10 articles)). Is it possible?

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  • UNIX-style RegExp Replace running extremely slowly under windows. Help?

    - by John Sullivan
    I'm trying to run a unix regEXP on every log file in a 1.12 GB directory, then replace the matched pattern with ''. Test run on a 4 meg file is took about 10 minutes, but worked. Obviously something is murdering performance by several orders of magnitude. Find: ^(?!.*155[0-2][0-9]{4}\s.*).*$ -- NOTE: match any line NOT starting 152[0-2]NNNN where in is a number 0-9. Replace with: ''. Is there some justifiable reason for my regExp to take this long to replace matching text, or is the program I am using (this is windows / a program called "grepWin") most likely poorly optimized? Thanks.

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  • Recurrance Calendar Issue in Lotus Notes

    - by Preeti
    Hi all, I am creating a Daily Reccurrance pattern in calendar items. But there is a issue as before clicking "save and Send Invitations" button, but in the Document Properties field i am able to view the RepeatForUnit and based on its value i am identifying the Reccurrance type like (D: for daily, W: for Weekly, M: for montlhy etc). But, After clicking on the "save and Send Invitations" button, the Recurrance is getting saved but after that, i am unable to get the RepeatForUnit field in Document Properties. Kindly help me, how to identify the Reccurrance type and the related fields. Note: I am using Domino.dll using C#. Regards, Preeti

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  • Type patterns in Haskell

    - by finnsson
    I'm trying to compile a simple example of generic classes / type patterns (see http://www.haskell.org/ghc/docs/latest/html/users_guide/generic-classes.html) in Haskell but it won't compile. Any ideas about what's wrong with the code would be helpful. According to the documentation there should be a module Generics with the data types Unit, :*:, and :+: but ghc (6.12.1) complaints about Not in scope: data constructor 'Unit' etc. It seems like there's a package instant-generics with the data types :*:, :+: and U but when I import that module (instead of Generics) I get the error Illegal type pattern in the generic bindings {myPrint _ = ""} The complete source code is import Generics.Instant class MyPrint a where myPrint :: a -> String myPrint {| U |} _ = "" myPrint {| a :*: b |} (x :*: y) = "" (show x) ++ ":*:" ++ (show y) myPrint {| a :+: b |} _ = "" data Foo = Foo String instance MyPrint a => MyPrint a main = myPrint $ Foo "hi" and I compile it using ghc --make Foo.hs -fglasgow-exts -XGenerics -XUndecidableInstances P.S. The module Generics export no data types, only the functions: canDoGenerics mkGenericRhs mkTyConGenericBinds validGenericInstanceType validGenericMethodType

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  • Java source code generation frameworks

    - by Superfilin
    I have a set of Java 5 source files with old-style Doclet tags, comments and annotations. And based on that I would like to write a generator for another set of Java classes. What is the best way to do that? And are there any good standalone libraries for code analysis/generation in Java? Any shared exprience in this field is appreciated. So, far I have found these: JaxME's Java Source Reflection - seems good, but it does not seem to support annotations. Also it had no release since 2006. Annogen - uses JDK's Doclet generator, which has some bugs under 1.5 JDK. Also it had no releases for a long time. Javaparser - seems good as well and pretty recent, but only supports Visitor pattern for a single class i.e. no query mechanism like in the 2 above packages.

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  • Dynamically loading JavaScript synchronously

    - by spoon16
    I'm using the module pattern, one of the things I want to do is dynamically include an external JavaScript file, execute the file, and then use the functions/variables in the file in the return { } of my module. I can't figure out how to do this easily. Are there any standard ways of performing a pseudo synchronous external script load? function myModule() { var tag = document.createElement("script"); tag.type = "text/javascript"; tag.src = "http://some/script.js"; document.getElementsByTagName('head')[0].appendChild(tag); //something should go here to ensure file is loaded before return is executed return { external: externalVariable } }

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  • Zend Framework - Database Table Singleton

    - by Sonny
    I have found myself doing this in my code to 'cache' the work done when instantiating my Zend_Db_Table models: if (Zend_Registry::isRegistered('x_table')) { $x_table = Zend_Registry::get('x_table'); } else { $x_table = new Default_Model_DbTable_X; Zend_Registry::set('x_table', $x_table); } It bothered me that this method isn't very DRY and it dawned on me today that a singleton pattern would probably be a better way to do this. Problem is, I've never written a singleton class. When I did some web searches, I found some offhand comments about Zend_Db_Table singletons, but no real examples. I already have meta-data caching configured. How do I make my Zend_Db_Table models singletons? Are there pitfalls or downsides?

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