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  • ASP.NET: aggregating validators in a user control

    - by orsogufo
    I am developing a web application where I would like to perform a set of validations on a certain field (an account name in the specific case). I need to check that the value is not empty, matches a certain pattern and is not already used. I tried to create a UserControl that aggregates a RequiredFieldValidator, a RegexValidator and a CustomValidator, then I created a ControlToValidate property like this: public partial class AccountNameValidator : System.Web.UI.UserControl { public string ControlToValidate { get { return ViewState["ControlToValidate"] as string; } set { ViewState["ControlToValidate"] = value; AccountNameRequiredFieldValidator.ControlToValidate = value; AccountNameRegexValidator.ControlToValidate = value; AccountNameUniqueValidator.ControlToValidate = value; } } } However, if I insert the control on a page and set ControlToValidate to some control ID, when the page loads I get an error that says Unable to find control id 'AccountName' referenced by the 'ControlToValidate' property of 'AccountNameRequiredFieldValidator', which makes me think that the controls inside my UserControl cannot resolve correctly the controls in the parent page. So, I have two questions: 1) Is it possible to have validator controls inside a UserControl validate a control in the parent page? 2) Is it correct and good practice to "aggregate" multiple validator controls in a UserControl? If not, what is the standard way to proceed?

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  • Detecting Asymptotes in a Graph

    - by nasufara
    I am creating a graphing calculator in Java as a project for my programming class. There are two main components to this calculator: the graph itself, which draws the line(s), and the equation evaluator, which takes in an equation as a String and... well, evaluates it. To create the line, I create a Path2D.Double instance, and loop through the points on the line. To do this, I calculate as many points as the graph is wide (e.g. if the graph itself is 500px wide, I calculate 500 points), and then scale it to the window of the graph. Now, this works perfectly for most any line. However, it does not when dealing with asymptotes. If, when calculating points, the graph encounters a domain error (such as 1/0), the graph closes the shape in the Path2D.Double instance and starts a new line, so that the line looks mathematically correct. Example: However, because of the way it scales, sometimes it is rendered correctly, sometimes it isn't. When it isn't, the actual asymptotic line is shown, because within those 500 points, it skipped over x = 2.0 in the equation 1 / (x-2), and only did x = 1.98 and x = 2.04, which are perfectly valid in that equation. Example: In that case, I increased the window on the left and right one unit each. My question is: Is there a way to deal with asymptotes using this method of scaling so that the resulting line looks mathematically correct? I myself have thought of implementing a binary search-esque method, where, if it finds that it calculates one point, and then the next point is wildly far away from the last point, it searches in between those points for a domain error. I had trouble figuring out how to make it work in practice, however. Thank you for any help you may give!

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  • GAE python database object design for simple list of values

    - by Joey
    I'm really new to database object design so please forgive any weirdness in my question. Basically, I am use Google AppEngine (Python) and contructing an object to track user info. One of these pieces of data is 40 Achievement scores. Do I make a list of ints in the User object for this? Or do I make a separate entity with my user id, the achievement index (0-39) and the score and then do a query to grab these 40 items every time I want to get the user data in total? The latter approach seems more object oriented to me, and certainly better if I extend it to have more than just scores for these 40 achievements. However, considering that I might not extend it, should I even consider just doing a simple list of 40 ints in my user data? I would then forgo doing a query, getting the sorted list of achievements, reading the score from each one just to process a response etc. Is doing this latter approach just such a common practice and hand-waved as not even worth batting an eyelash at in terms of thinking it might be more costly or complex processing wise?

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  • How to localize an app on Google App Engine?

    - by Petri Pennanen
    What options are there for localizing an app on Google App Engine? How do you do it using Webapp, Django, web2py or [insert framework here]. 1. Readable URLs and entity key names Readable URLs are good for usability and search engine optimization (Stack Overflow is a good example on how to do it). On Google App Engine, key based queries are recommended for performance reasons. It follows that it is good practice to use the entity key name in the URL, so that the entity can be fetched from the datastore as quickly as possible. Currently I use the function below to create key names: import re import unicodedata def urlify(unicode_string): """Translates latin1 unicode strings to url friendly ASCII. Converts accented latin1 characters to their non-accented ASCII counterparts, converts to lowercase, converts spaces to hyphens and removes all characters that are not alphanumeric ASCII. Arguments unicode_string: Unicode encoded string. Returns String consisting of alphanumeric (ASCII) characters and hyphens. """ str = unicodedata.normalize('NFKD', unicode_string).encode('ASCII', 'ignore') str = re.sub('[^\w\s-]', '', str).strip().lower() return re.sub('[-\s]+', '-', str) This works fine for English and Swedish, however it will fail for non-western scripts and remove letters from some western ones (like Norwegian and Danish with their œ and ø). Can anyone suggest a method that works with more languages? 2. Translating templates Does Django internationalization and localization work on Google App Engine? Are there any extra steps that must be performed? Is it possible to use Django i18n and l10n for Django templates while using Webapp? The Jinja2 template language provides integration with Babel. How well does this work, in your experience? What options are avilable for your chosen template language? 3. Translated datastore content When serving content from (or storing it to) the datastore: Is there a better way than getting the *accept_language* parameter from the HTTP request and matching this with a language property that you have set with each entity?

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  • Reading component parameters and setting defaults

    - by donut
    I'm pulling my hair on this because it should be simple, but can't get it to do the right thing. What's the best practice way of doing the following I've created a custom component that extends <s:Label> so now the Label has additional properties color2 color3 value which can be called like this and are used in the skin. <s:CustomLabel text="Some text" color2="0x939202" color3="0x999999" value="4.5" /> If I don't supply these parameters, I'd like some defaults to be set. So far I've had some success, but it doesn't work 100% of the time, which leads me to think that I'm not following best practices when setting those defaults. I do it now like this: [Bindable] private var myColor2:uint = 0x000000; [Bindable] private var myColor3:uint = 0x000000; [Bindable] private var myValue:Number = 10.0; then in the init function, I do a variation of this to set the default myValue = hostComponent.value; myValue = (hostComponent.value) ? hostComponent.value : 4.5; Sometimes it works, sometimes it doesn't, depending on the type of variable I'm trying to set. I eventually decided to read them as Strings then convert them to the desired type, but it seems that this also works half the time.

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  • CQRS - The query side

    - by mattcodes
    A lot of the blogsphere articles related to CQRS (command query repsonsibility) seperation seem to imply that all screens/viewmodels are flat. e.g. Name, Age, Location Of Birth etc.. and thus the suggestion that implementation wise we stick them into fast read source etc.. single table per view mySQL etc.. and pull them out with something like primitive SqlDataReader, kick that nasty nhibernate ORM etc.. However, whilst I agree that domain models dont mapped well to most screens, many of the screens that I work with are more dimensional, and Im sure this is pretty common in LOB apps. So my question is how are people handling screen where by for example it displays a summary of customer details and then a list of their orders with a [more detail] link etc.... I thought about keeping with the straight forward SQL query to the Query Database breaking off the outer join so can build a suitable ViewModel to View but it seems like overkill? Alternatively (this is starting to feel yuck) in CustomerSummaryView table have a text/big (whatever the type is in your DB) column called Orders, and the columns for the Order summary screen grid are seperated by , and rows by |. Even with XML datatype it still feeel dirty. Any thoughts on an optimal practice?

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  • DDD and Client/Server apps

    - by Christophe Herreman
    I was wondering if any of you had successfully implemented DDD in a Client/Server app and would like to share some experiences. We are currently working on a smart client in Flex and a backend in Java. On the server we have a service layer exposed to the client that offers CRUD operations amongst some other service methods. I understand that in DDD these services should be repositories and services should be used to handle use cases that do not fit inside a repository. Right now, we mimic these services on the client behind an interface and inject implementations (Webservices, RMI, etc) via an IoC container. So some questions arise: should the server expose repositories to the client or do we need to have some sort of a facade (that is able to handle security for instance) should the client implement repositories (and DDD in general?) knowing that in the client, most of the logic is view related and real business logic lives on the server. All communication with the server happens asynchronously and we have a single threaded programming model on the client. how about mapping client to server objects and vice versa? We tried DTO's but reverted back to exposing the state of our objects and mapping directly to them. I know this is considered bad practice, but it saves us an incredible amount of time) In general I think a new generation of applications is coming with the growth of Flex, Silverlight, JavaFX and I'm curious how DDD fits into this.

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  • Newbie database index question

    - by RenderIn
    I have a table with multiple indexes, several of which duplicate the same columns: Index 1 columns: X, B, C, D Index 2 columns: Y, B, C, D Index 3 columns: Z, B, C, D I'm not very knowledgeable on indexing in practice, so I'm wondering if somebody can explain why X, Y and Z were paired with these same columns. B is an effective date. C is a semi-unique key ID for this table for a specific effective date B. D is a sequence that identifies the priority of this record for the identifier C. Why not just create 6 indexes, one for each X, Y, Z, B, C, D? I want to add an index to another column T, but in some contexts I'll only be querying on T alone while in others I will also be specifying the B, C and D columns... so should I create just one index like above or should I create one for T and one for (T, B, C, D)? I've not had as much luck as expected when googling for comprehensive coverage of indexing. Any resources where I can get a through explanation and lots of examples of B-tree indexing?

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  • How can I write classes that don't rely on "global" variables?

    - by Joel
    When I took my first programming course in university, we were taught that global variables were evil & should be avoided at all cost (since you can quickly develop confusing and unmaintainable code). The following year, we were taught object oriented programming, and how to create modular code using classes. I find that whenever I work with OOP, I use my classes' private variables as global variables, i.e., they can be (and are) read and modified by any function within the class. This isn't really sitting right with me, as it seems to introduce the same problems global variables had in languages like C. So I guess my question is, how do I stop writing classes with "global" variables? Would it make more sense to pretend I'm writing in a functional language? By this I mean having all functions take parameters & return values instead of directly modifying class variables. If I need to set any fields, I can just take the output of the function and assign it instead of having the function do it directly. This seems like it might make more maintainable code, at least for larger classes. What's common practice? Thanks!

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  • PCA extended face recognition

    - by cMinor
    The state of the art says that we can use PCA to perform face recognition. like this, this or this I am working with a project that involves training a classifier to detect a person who is wearing glasess or hats or even a mustache. The purpose of doing this is to detect when a person that has robbed a bank, store, or have commeted some sort of crime(s) (we have their image in a database), enters a certain place ( historically we know these guys have robbed, so we should take care to avoid problems). We came first to have a distributed database with all images of criminals, then I thought to have a layer of them clasifying these criminals using accesories like hats, mustache or anything that hides their face etc... Then, to apply that knowledge to detect when a particular or a suspect person enters a comercial place. ( In practice when someone is going to rob not all the times they are using an accesorie...) What do you think about this idea of doing PCA to first detect principal components of the face and then the components of an accesory. I was thinking that maybe a probabilistic approach is better so we can compute the probability the criminal is the person that entered a place and call the respective authorities.

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  • Converting an input text value to a decimal number

    - by vitto
    Hi, I'm trying to work with decimal data in my PHP and MySql practice and I'm not sure about how can I do for an acceptable level af accuracy. I've wrote a simple function which recives my input text value and converts it to a decimal number ready to be stored in the database. <?php function unit ($value, $decimal_point = 2) { return number_format (str_replace (",", ".", strip_tags (trim ($value))), $decimal_point); } ?> I've resolved something like AbdlBsF5%?nl with some jQuery code for replace and some regex to keep only numbers, dots and commas. In some country, people uses the comma , to send decimal numbers, so a number like 72.08 is wrote like 72,08. I'd like avoid to forcing people to change their usual chars and I've decided to use a jQuery to keep this too. Now every web developer knows the last validation must be handled by the dynamic page for security reasons. So my answer is should I use something like unit (); function to store data or shoul I also check if users inserts invalid chars like letters or something else? If I try this and send letters, the query works without save the invalid data, I think this isn't bad, but I could easily be wrong because I'm a rookie. What kind of method should I use if I want a number like 99999.99 for my query?

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  • How to display a subview loaded from a separate NIB file

    - by Marcus Netter
    I'm developing a Cocoa desktop application that uses a source list in the style of iTunes: different elements in the source list cause the main content area to display different views. The content area is entirely filled with a (vertical) NSSplitView; on the left is an NSOutlineView source list. When the user selects an item on the left, the relevant view appears on the right side of the splitter. I can make it work well enough by putting everything in one NIB file and putting a borderless NSTabView to the right of the splitter; to switch views, I just have to change the selected tab. But putting all the views in one NIB is bad practice, so I'm trying to move each of the subviews into their own NIB files. I have a pretty good idea of most of this process — I've created an NSViewController subclass for each of these views (EntityDetailViewController, GroupDetailViewController, and so on), set the File's Owner of each new NIB to the relevant controller class, set the view connection in each NIB, and reworked the bindings. What I don't know is how to actually change which subview is being shown on screen. I've tried using the default generic NSView on the right side and sending it addSubview: messages; I've tried connecting to it as the first subview and calling NSView *newSubview = /* get subview from the new subview controller */ [[subview superview] replaceSubview:subview with:newSubview]; [self setSubview:newSubview]; But everything just leaves the space blank. How do I display a subview loaded from a separate NIB?

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  • Retrieve COM ProgID from exe without registering it

    - by mangelo
    Background: I would like to extract the COM data from a VB6 application so I can register it correctly (according to Microsoft best practice) the application. I am using WiX 3.0 and heat.exe will not extract the data (known issue with heat) and I do not have ready access to the associated TLB file. The VB6 application does not have compatibility turned on so it regenerates the COM GUIDs every build (They want to have the application be able to run side by side with an older version.) I created a C# application that will collect the TypeLib, interface and CoClass information from the VB6 application without registering it and create a wxs file for candle to use. My company has several other older applications like this and I would like to make it a more generic solution. The Issues: 1.Is there a way to collect the 'true' ProgID (programmer intended one) from the application with out the project or TLB file and without registering it? 2.Is there a way to find out the intended Threading Model from a DLL without registering it? (I intend that it can handle all COM active items, might as well be complete) Thank you.

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  • Direct invocation vs indirect invocation in C

    - by Mohit Deshpande
    I am new to C and I was reading about how pointers "point" to the address of another variable. So I have tried indirect invocation and direct invocation and received the same results (as any C/C++ developer could have predicted). This is what I did: int cost; int *cost_ptr; int main() { cost_ptr = &cost; //assign pointer to cost cost = 100; //intialize cost with a value printf("\nDirect Access: %d", cost); cost = 0; //reset the value *cost_ptr = 100; printf("\nIndirect Access: %d", *cost_ptr); //some code here return 0; //1 } So I am wondering if indirect invocation with pointers has any advantages over direct invocation or vice-versa. Some advantages/disadvantages could include speed, amount of memory consumed performing the operation (most likely the same but I just wanted to put that out there), safeness (like dangling pointers) , good programming practice, etc. 1Funny thing, I am using the GNU C Compiler (gcc) and it still compiles without the return statement and everything is as expected. Maybe because the C++ compiler will automatically insert the return statement if you forget.

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  • jQuery eval of ajax inline script not throwing errors

    - by Josh
    http://stackoverflow.com/questions/606794/debugging-ajax-code-with-firebug This question is quite similar, though old and without real answers. I'm currently putting together an app that has scripts that get loaded in with an ajax request. An example: var main = _main.get(); main.load( someurl ); Where someurl is a page that contains an inline script element: <script type="text/javascript"> $(document).ready( function(){ var activities = new activities(); activities.init(); }); </script> jQuery will do a line by line eval of js that lives in inline script tags. The problem is, I get no errors or any information whatsoever in firebug when something goes awry. Does anyone have a good solution for this? Or a better practice for loading pages which contain javascript functionality? Edit: A little progress... so at the top of the page that is being loaded in via ajax, I have another script that was being included like this: <script type="text/javascript" src="javascript/pages/activities.js"></script> When I moved the inline $(document).ready() code in the page to the end of this included file, instead, syntax errors were now properly getting thrown. As an aside, I threw a console.log() into the inline script tag, and it was being logged just fine. I also tried removing the $(document).ready() altogether, and also switching it out for a $(window).load() event. No difference. May have something to do with the inline scripts dependency on the included activities.js, I guess. :: shakes head :: javascript can be a nightmare.

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  • An implementation of Sharir's or Aurenhammer's deterministic algorithm for calculating the intersect

    - by RGrey
    The problem of finding the intersection/union of 'N' discs/circles on a flat plane was first proposed by M. I. Shamos in his 1978 thesis: Shamos, M. I. “Computational Geometry” Ph.D. thesis, Yale Univ., New Haven, CT 1978. Since then, in 1985, Micha Sharir presented an O(n log2n) time and O(n) space deterministic algorithm for the disc intersection/union problem (based on modified Voronoi diagrams): Sharir, M. Intersection and closest-pair problems for a set of planar discs. SIAM .J Comput. 14 (1985), pp. 448-468. In 1988, Franz Aurenhammer presented a more efficient O(n log n) time and O(n) space algorithm for circle intersection/union using power diagrams (generalizations of Voronoi diagrams): Aurenhammer, F. Improved algorithms for discs and balls using power diagrams. Journal of Algorithms 9 (1985), pp. 151-161. Earlier in 1983, Paul G. Spirakis also presented an O(n^2) time deterministic algorithm, and an O(n) probabilistic algorithm: Spirakis, P.G. Very Fast Algorithms for the Area of the Union of Many Circles. Rep. 98, Dept. Comput. Sci., Courant Institute, New York University, 1983. I've been searching for any implementations of the algorithms above, focusing on computational geometry packages, and I haven't found anything yet. As neither appear trivial to put into practice, it would be really neat if someone could point me in the right direction!

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  • Duck type testing with C# 4 for dynamic objects.

    - by Tracker1
    I'm wanting to have a simple duck typing example in C# using dynamic objects. It would seem to me, that a dynamic object should have HasValue/HasProperty/HasMethod methods with a single string parameter for the name of the value, property, or method you are looking for before trying to run against it. I'm trying to avoid try/catch blocks, and deeper reflection if possible. It just seems to be a common practice for duck typing in dynamic languages (JS, Ruby, Python etc.) that is to test for a property/method before trying to use it, then falling back to a default, or throwing a controlled exception. The example below is basically what I want to accomplish. If the methods described above don't exist, does anyone have premade extension methods for dynamic that will do this? Example: In JavaScript I can test for a method on an object fairly easily. //JavaScript function quack(duck) { if (duck && typeof duck.quack === "function") { return duck.quack(); } return null; //nothing to return, not a duck } How would I do the same in C#? //C# 4 dynamic Quack(dynamic duck) { //how do I test that the duck is not null, //and has a quack method? //if it doesn't quack, return null }

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  • VS2008 adding SQL Server Database (SQL Server 2008 Mgmt Studio) not working

    - by Kahn
    I'm trying to practice using the ASP.Net MVC at home, but I ran into an impossible problem. I cannot open a connection to SQL Server 2008, I get this error: "Connections to SQL Server files (*.mdf) require SQL Server Express 2005 to function properly. ..." I've googled around for numerous responses, none of them either working or addressing this issue. I'm running Vista 32bit, my SQL Server 2008 Mgmt Studio is also 32bit, I have SP1 installed both on VS2008 Professional, as well as the SQL Server. I changed the machine.config connectionStrings from ./SQLExpress to my SQL Server 2008 name. Now if I connect manually through web.config, in an asp:datasource or code-behind, everything works fine. But for some reason trying to add a DB Connection directly like this always gets the error. This is pretty fatal, since I can't rightly do much unless I can use LINQ to SQL with my MVC test project, and this is the only way I know how. Worked fine in school and work, but not at home. Installing SQL Server Express 2005, as some have suggested, is not an option. Obviously it HAS to work with SQL Server 2008. Thanks in advance.

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  • "Undefined symbols" linker error with simple template class

    - by intregus
    Been away from C++ for a few years and am getting a linker error from the following code: Gene.h #ifndef GENE_H_INCLUDED #define GENE_H_INCLUDED template <typename T> class Gene { public: T getValue(); void setValue(T value); void setRange(T min, T max); private: T value; T minValue; T maxValue; }; #endif // GENE_H_INCLUDED Gene.cpp #include "Gene.h" template <typename T> T Gene<T>::getValue() { return this->value; } template <typename T> void Gene<T>::setValue(T value) { if(value >= this->minValue && value <= this->minValue) { this->value = value; } } template <typename T> void Gene<T>::setRange(T min, T max) { this->minValue = min; this->maxValue = max; } Using Code::Blocks and GCC if it matters to anyone. Also, clearly porting some GA stuff to C++ for fun and practice.

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  • Embedding a CMS in an MVC Web App

    - by Mr Snuffle
    I'm working on a website for searching for businesses, then displaying a listing page. We've been toying with the idea of letting the clients manage their listing page using an external CMS. I'm not sure how often this is done, or if it's even best practice. Ideally, we want to be able to setup a listing on our website, then give the clients access to an external CRM when they can manage their listing page. We then want to embed this custom page within our website, possibly using an iframe (which will come along with it's own set of complications). We'd like this integration to be as seamless as possible. I'd personally prefer it if we could directly inject the HTML into our own page and bypass an iframe all together, but I don't know of any CMS hosting services that provide the interface for such a thing. We've experimented a little with Squarespace, and we can get a fairly clean version of someone's page which would be well suited for an iframe. I'm wondering if anyone else has looked and integrating an external hosting CMS into a website (in this case, we're using ASP.NET MVC). We'd also want to automate the creation of accounts on this external CMS, so when a user signed up we could just point them to the website with some login details. I have no idea if anyone offers a service like this, but any recommendations would be greatly appreciated. We could host a service ourself too, but the aim is to have an external system that clients can use to manage their pages. Cheers, James

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  • Dashcode code translation

    - by Alex Mcp
    Hi, a quick, probably easy question whose answer is probably "best practice" I'm following a tutorial for a custom-template mobile Safari webapp, and to change views around this code is used: function btnSave_ClickHandler(event) { var views = document.getElementById('stackLayout'); var front = document.getElementById('mainScreen'); if (views && views.object && front) { views.object.setCurrentView(front, true); } } My question is just about the if conditional statement. What is this triplet saying, and why do each of those things need to be verified before the view can be changed? Does views.object just test to see if the views variable responds to the object method? Why is this important? EDIT - This is/was the main point of this question, and it regards not Javascript as a language and how if loops work, but rather WHY these 3 things specifically need to be checked: Under what scenarios might views and front not exist? I don't typically write my code so redundantly. If the name of my MySQL table isn't changing, I'll just say UPDATE 'mytable' WHERE... instead of the much more verbose (and in my view, redundant) $mytable = "TheSQLTableName"; if ($mytable == an actual table && $mytable exists && entries can be updated){ UPDATE $mytable; } Whereas if the table's name (or in the JS example, the view's names) ARE NOT "hard coded" but are instead a user input or otherwise mutable, I might right my code as the DashCode example has it. So tell me, can these values "go wrong" anyhow? Thanks!

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  • In Ruby, how to implement global behaviour?

    - by Gordon McAllister
    Hi all, I want to implement the concept of a Workspace. This is a global concept - all other code will interact with one instance of this Workspace. The Workspace will be responsible for maintaining the current system state (i.e. interacting with the system model, persisting the system state etc) So what's the best design strategy for my Workspace, bearing in mind this will have to be testable (using RSpec now, but happy to look at alternatives). Having read thru some open source projects out there and I've seen 3 strategies. None of which I can identify as "the best practice". They are: Include the singleton class. But how testable is this? Will the global state of Workspace change between tests? Implemented all behaviour as class methods. Again how do you test this? Implemented all behaviour as module methods. Not sure about this one at all! Which is best? Or is there another way? Thanks, Gordon

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  • Running another process without GUI freezing

    - by Adam
    I'm having trouble getting my GUI to appear and not freeze while running (and waiting for) an outside process. In this case, drivers.exe is a very simply program where the user simply clicks "OK". So whenever I click OK, it exits. I am trying to simply make my status strip count numbers up (really fast) as drivers.exe is executing. But in practice, my GUI never appears at all until drivers.exe exits. private void run_drivers() { Console.WriteLine("Start Driver"); int driver_timeout_in_minutes = 20; System.Diagnostics.Process driverproc = System.Diagnostics.Process.Start(Application.StartupPath + "\\" + "drivers.exe"); driverproc.WaitForExit(driver_timeout_in_minutes * 1000 * 60); //uses milliseconds, we must convert } private void Form1_Load(object sender, EventArgs e) { ThreadStart worker = new ThreadStart(run_drivers); Console.WriteLine("Main - Creating worker thread"); toolStripStatusLabel1.Text = "hi"; Thread t = new Thread(worker); t.IsBackground = true; t.Start(); Console.WriteLine("Main - Have requested the start of worker thread"); int i = 0; while (t.IsAlive) { i++; toolStripStatusLabel1.Text = i.ToString(); } Console.WriteLine("Dead"); }

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  • When does invoking a member function on a null instance result in undefined behavior?

    - by GMan
    This question arose in the comments of a now-deleted answer to this other question. Our question was asked in the comments by STingRaySC as: Where exactly do we invoke UB? Is it calling a member function through an invalid pointer? Or is it calling a member function that accesses member data through an invalid pointer? With the answer deleted I figured we might as well make it it's own question. Consider the following code: #include <iostream> struct foo { void bar(void) { std::cout << "gman was here" << std::endl; } void baz(void) { x = 5; } int x; }; int main(void) { foo* f = 0; f->bar(); // (a) f->baz(); // (b) } We expect (b) to crash, because there is no corresponding member x for the null pointer. In practice, (a) doesn't crash because the this pointer is never used. Because (b) dereferences the this pointer (this->x = 5;), and this is null, the program enters undefined behavior. Does (a) result in undefined behavior? What about if both functions are static?

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  • How to use bll, dal and model?

    - by bruno
    Dear all, In my company I must use a Bll, Dal and model layer for creating applications with a database. I've learned at school that every databasetable should be an object in my model. so I create the whole model of my database. Also I've learned that for every table (or model object) there should be a DAO created into the DAL. So I do this to. Now i'm stuck with the BLL classes. I can write a BLLclass for each DAO/ModelObject or I can write a BLLclass that combine some (logic) DAO's... Or i can write just one Bllclass that will manage everything. (this last one I'm sure it aint the best way..) What is the best practice to handle this Bll 'problem'? And a second question. If a bll is in need of tablecontent from an other table where it aint responsible for, whats the best way to get the content? Go ask on the responsible BLL or go directly to the DAO? I'm struggling with these questions the last 2 months, and i don't know what is the best way to handle it.

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