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  • javascript: execute a bunch of asynchronous method with one callback

    - by Samuel Michelot
    I need to execute a bunch of asynchronous methods (client SQLite database), and call only one final callback. Of course, the ugly way is: execAll : function(callBack) { asynch1(function() { asynch2(function() { ... asynchN(function() { callBack(); }) }) }); } But I know there are better ways to do it. Intuitively I would detect when all call back has been called with a counter to call the final callback. I think this is a common design-pattern, so if someone could point me in the right direction... Thanks in advance !

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  • Risking the exception anti-pattern.. with some modifications

    - by Sridhar Iyer
    Lets say that I have a library which runs 24x7 on certain machines. Even if the code is rock solid, a hardware fault can sooner or later trigger an exception. I would like to have some sort of failsafe in position for events like this. One approach would be to write wrapper functions that encapsulate each api a: returnCode=DEFAULT; try { returnCode=libraryAPI1(); } catch(...) { returnCode=BAD; } return returnCode; The caller of the library then restarts the whole thread, reinitializes the module if the returnCode is bad. Things CAN go horribly wrong. E.g. if the try block(or libraryAPI1()) had: func1(); char *x=malloc(1000); func2(); if func2() throws an exception, x will never be freed. On a similar vein, file corruption is a possible outcome. Could you please tell me what other things can possibly go wrong in this scenario?

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  • Writing user stories for internal technical tasks

    - by John Nolan
    I am attempting to manage my projects a little better so I am looking at attempting to apply some of (eventually all) the features of scrum. Looking at user stories specifically the high level format seems to be: As a User I can Feature Description or Artifact is Doing Something How would I write "Upgrade the Database"? Is it simply Upgrade the Database? I think I am being thrown off as there is no specific actor/customer and that the customer is the IT department.

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  • creational pattern for instances depending on multiple subclass instances

    - by markusw
    I have a problem, for that I was not able to identify a suitable design pattern. I want to create instances depending on a given type that has been passed to a factory method. What I am doing until now is the following: T create(SuperType x) { if (x instanceof SubType1) { // do some stuff and return a new SubType extends T } else if (x instanceof SubType2) { // do some stuff and return a new SubType extends T } else if ... } else { throw new UnSupportedOperationException("nothing defined for " + x); } } It seems not to be best pratice for me. Has anybody an idea how to solve this in a better way?

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  • Which is the better C# class design for dealing with read+write versus readonly

    - by DanM
    I'm contemplating two different class designs for handling a situation where some repositories are read-only while others are read-write. (I don't foresee any need to a write-only repository.) Class Design 1 -- provide all functionality in a base class, then expose applicable functionality publicly in sub classes public abstract class RepositoryBase { protected virtual void SelectBase() { // implementation... } protected virtual void InsertBase() { // implementation... } protected virtual void UpdateBase() { // implementation... } protected virtual void DeleteBase() { // implementation... } } public class ReadOnlyRepository : RepositoryBase { public void Select() { SelectBase(); } } public class ReadWriteRepository : RepositoryBase { public void Select() { SelectBase(); } public void Insert() { InsertBase(); } public void Update() { UpdateBase(); } public void Delete() { DeleteBase(); } } Class Design 2 - read-write class inherits from read-only class public class ReadOnlyRepository { public void Select() { // implementation... } } public class ReadWriteRepository : ReadOnlyRepository { public void Insert() { // implementation... } public void Update() { // implementation... } public void Delete() { // implementation... } } Is one of these designs clearly stronger than the other? If so, which one and why? P.S. If this sounds like a homework question, it's not, but feel free to use it as one if you want :)

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  • Generalized plugable caching pattern?

    - by BCS
    Given that it's one of the hard things in computer science, does anyone know of a way to set up a plugable caching strategy? What I'm thinking of would allow me to write a program with minimal thought as to what needs to be cached (e.i. use some sort of boiler-plate, low/no cost pattern that compiles away to nothing anywhere I might want caching) and then when things are further along and I know where I need caching I can add it in without making invasive code changes. As an idea to the kind of solution I'm looking for; I'm working with the D programing language (but halfway sane C++ would be fine) and I like template.

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  • Singleton Pattern combine with a Decorator

    - by Mike
    Attached is a classic Decorator pattern. My question is how would you modify the below code so that you can wrap zero or one of each topping on to the Pizza Right now I can have a Pepporini - Sausage -- Pepporini -- Pizza class driving the total cost up to $10, charging twice for Pepporini. I don't think I want to use the Chain of Responsibility pattern as order does not matter and not all toppings are used? Thank you namespace PizzaDecorator { public interface IPizza { double CalculateCost(); } public class Pizza: IPizza { public Pizza() { } public double CalculateCost() { return 8.00; } } public abstract class Topping : IPizza { protected IPizza _pizzaItem; public Topping(IPizza pizzaItem) { this._pizzaItem = pizzaItem; } public abstract double CalculateCost(); } public class Pepporini : Topping { public Pepporini(IPizza pizzaItem) : base(pizzaItem) { } public override double CalculateCost() { return this._pizzaItem.CalculateCost() + 0.50; } } public class Sausage : Topping { public Sausage(IPizza pizzaItem) : base(pizzaItem) { } public override double CalculateCost() { return this._pizzaItem.CalculateCost() + 1.00; } } public class Onions : Topping { public Onions(IPizza pizzaItem) : base(pizzaItem) { } public override double CalculateCost() { return this._pizzaItem.CalculateCost() + .25; } } }

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  • UINavigation Bar while moving view for writing in a textfield

    - by ObiWanKeNerd
    i'm using this code to move the view when i'm about to type on a textfield, otherwise the keyboard may cover the textfield if it's in the lower side of the screen. I would like to know if there is a way to maintain the UINavigation Bar in it's place, because with this code the bar will move with all the view outside the screen, becoming untouchable until i end editing the textfield (closing the keyboard). CGFloat animatedDistance; static const CGFloat KEYBOARD_ANIMATION_DURATION = 0.3; static const CGFloat MINIMUM_SCROLL_FRACTION = 0.2; static const CGFloat MAXIMUM_SCROLL_FRACTION = 0.8; static const CGFloat PORTRAIT_KEYBOARD_HEIGHT = 216; static const CGFloat LANDSCAPE_KEYBOARD_HEIGHT = 162; - (void)textFieldDidBeginEditing:(UITextField *)textField { CGRect textFieldRect = [self.view.window convertRect:textField.bounds fromView:textField]; CGRect viewRect = [self.view.window convertRect:self.view.bounds fromView:self.view]; CGFloat midline = textFieldRect.origin.y + 0.5 * textFieldRect.size.height; CGFloat numerator = midline - viewRect.origin.y - MINIMUM_SCROLL_FRACTION * viewRect.size.height; CGFloat denominator = (MAXIMUM_SCROLL_FRACTION - MINIMUM_SCROLL_FRACTION) * viewRect.size.height; CGFloat heightFraction = numerator / denominator; if (heightFraction < 0.0) { heightFraction = 0.0; } else if (heightFraction > 1.0) { heightFraction = 1.0; } UIInterfaceOrientation orientation = [[UIApplication sharedApplication] statusBarOrientation]; if (orientation == UIInterfaceOrientationPortrait || orientation == UIInterfaceOrientationPortraitUpsideDown) { animatedDistance = floor(PORTRAIT_KEYBOARD_HEIGHT * heightFraction); } else { animatedDistance = floor(LANDSCAPE_KEYBOARD_HEIGHT * heightFraction); } CGRect viewFrame = self.view.frame; viewFrame.origin.y -= animatedDistance; [UIView beginAnimations:nil context:NULL]; [UIView setAnimationBeginsFromCurrentState:YES]; [UIView setAnimationDuration:KEYBOARD_ANIMATION_DURATION]; [self.view setFrame:viewFrame]; [UIView commitAnimations]; } - (void)textFieldDidEndEditing:(UITextField *)textField { CGRect viewFrame = self.view.frame; viewFrame.origin.y += animatedDistance; [UIView beginAnimations:nil context:NULL]; [UIView setAnimationBeginsFromCurrentState:YES]; [UIView setAnimationDuration:KEYBOARD_ANIMATION_DURATION]; [self.view setFrame:viewFrame]; [UIView commitAnimations]; } Thanks in advance!

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  • Writing a simple incrementing counter in rails

    - by Trip
    For every Card, I would like to attach a special number to them that increments by one. I assume I can do this all in the controller. def create @card = Card.new(params[:card]) @card.SpecNum = @card.SpecNum ++ ... end Or. I can be blatantly retarded. And maybe the best bet is to add an auto-incremement table to mysql. The problem is the number has to start at a specific number, 1020. Any ideas?

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  • Is it ok to dynamic cast "this" as a return value?

    - by Panayiotis Karabassis
    This is more of a design question. I have a template class, and I want to add extra methods to it depending on the template type. To practice the DRY principle, I have come up with this pattern (definitions intentionally omitted): template <class T> class BaseVector: public boost::array<T, 3> { protected: BaseVector<T>(const T x, const T y, const T z); public: bool operator == (const Vector<T> &other) const; Vector<T> operator + (const Vector<T> &other) const; Vector<T> operator - (const Vector<T> &other) const; Vector<T> &operator += (const Vector<T> &other) { (*this)[0] += other[0]; (*this)[1] += other[1]; (*this)[2] += other[2]; return *dynamic_cast<Vector<T> * const>(this); } } template <class T> class Vector : public BaseVector<T> { public: Vector<T>(const T x, const T y, const T z) : BaseVector<T>(x, y, z) { } }; template <> class Vector<double> : public BaseVector<double> { public: Vector<double>(const double x, const double y, const double z); Vector<double>(const Vector<int> &other); double norm() const; }; I intend BaseVector to be nothing more than an implementation detail. This works, but I am concerned about operator+=. My question is: is the dynamic cast of the this pointer a code smell? Is there a better way to achieve what I am trying to do (avoid code duplication, and unnecessary casts in the user code)? Or am I safe since, the BaseVector constructor is private?

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  • How to create new account using servlets

    - by Alvin
    I want to know how can I create new account using servlets in post method? I'm currently following MVC design pattern, and I want to know if I pass the required data to register new account from JSP page, then how can I get that data in post method? As request.getParameter() method returning me null. How can I know that post method is calling to create new account? How can I pass all the relevant user information from servlets to model class for registering data to the database table?

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  • Writing an image to ResponseBase.OutputStream does not work anymore with ASP.NET MVC2 RC2

    - by labilbe
    The following code worked nice on ASP.NET MVC1 public class ImageResult : ActionResult { public Image Image { get; set; } public override void ExecuteResult(ControllerContext context) { if (Image == null) { return; } HttpResponseBase response = context.HttpContext.Response; response.ContentType = "image/png"; Image.Save(response.OutputStream, ImageFormat.Png); } } I spent some time searching answers but I didn't find anyone. The error thrown is OutputStream is not available when a custom TextWriter is used.

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  • Problem implementing Interceptor pattern

    - by ph0enix
    I'm attempting to develop an Interceptor framework (in C#) where I can simply implement some interfaces, and through the use of some static initialization, register all my Interceptors with a common Dispatcher to be invoked at a later time. The problem lies in the fact that my Interceptor implementations are never actually referenced by my application so the static constructors never get called, and as a result, the Interceptors are never registered. If possible, I would like to keep all references to my Interceptor libraries out of my application, as this is my way of (hopefully) enforcing loose coupling across different modules. Hopefully this makes some sense. Let me know if there's anything I can clarify... Does anyone have any ideas, or perhaps a better way to go about implementing my Interceptor pattern? Update: I came across Spring.NET. I've heard of it before, but never really looked into it. It sounds like it has a lot of great features that would be very useful for what I'm trying to do. Does anyone have any experience with Spring.NET? TIA, Jeremy

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  • OutputStream with ByteArrayOutputStream not writing

    - by Yonatan
    Hey again Internet ! So i'm trying to write out an object to a ByteArray, but for some reason it's not writting anything, which i see by the fact that the return value is 0, and that by the fact that reading it results in an exception. BAoutput = new ByteArrayOutputStream(); Oout = new ObjectOutputStream(BAoutput); Oout.writeObject(receiver); where receiver is an object i get through a parameter. and the exceptions are always the same: at java.io.ObjectInputStream$BlockDataInputStream.peekByte(Unknown Source) at java.io.ObjectInputStream.readObject0(Unknown Source) at java.io.ObjectInputStream.readObject(Unknown Source) Any ideas?

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  • What design pattern shall I use in this question?

    - by iyad al aqel
    To be frank, this is a homework question, so I'll tell you my opinion. Can you let me know my mistakes rather than giving me the solution? This is the question : Assume a restaurant that only offers the following two types of meals: (a) a full meal and (b)an economic meal. The full meal consists of the following food items and is served in the following order: 1. Appetizer 2. Drink 3. Main dish 4. Dessert Meanwhile the economic meal consists of the following food items and is served in the following order: 1. Drink 2. Main dish Identify the most appropriate design pattern that can be used to allow a customer to only order using one of the two types of meals provided and that the meal components must be served in the given order. I'm confused between the Factory and the Iterator and using them both together. Using the factory Pattern we can create the two meals full and economic and provide the user with with a base object class that will decide upon. But how can we enforce the ordering of the elements, I thought of using the iterator along that will iterate through the the composite of the two created factories sort of speak. What do you think?

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  • Getting error in MVC Proj while writing Lambda Expression

    - by Shrewd Demon
    hi, i am creating a sample movie (MVC) application. I was getting fine with Viewing and Creating a new record, but when i wrote the code to get the details of a particular record i met with the following error: Unable to cast objec`t of type 'System.Data.Objects.ObjectQuery`1[MovieApp.Models.Movie]' to type 'MovieApp.Model`s.Movie'. here is the code i wrote for getting the details public ActionResult Details(int id) { var moviedetail = (Movie)_entities.MovieSet.Where(mvid => mvid.Id == id); return View(moviedetail); } can any body tell me whats going wrong and where ?? thank you.

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  • wcf trying to set up tracing to debug, not writing to log file

    - by joey j
    here's my web.config, running a WCF service in an application on IIS7, but nothing is being written to the specified file. permission on the file has been granted for everyone. </listeners> I can add a service reference just fine. I then try to call the service from a windows app and, after a few minutes, get an error on the machine running the windows app "Client is unable to finish the security negotiation within the configured timeout (00:00:00). The current negotiation leg is 1 (00:00:00)." but absolutely nothing is written to the trace log file specified in config. Is there something else I need to do to enable tracing? thanks for your help EDIT: "sources" section now matches the section recommended here: http://msdn.microsoft.com/en-us/library/aa702726.aspx I've added the "diagnostics and the event viewer shows: "Message Logging has been turned on. Sensitive information may be logged in the clear, even if it was encrypted on the wire: for example, message bodies. Process Name: w3wp Process ID: 1784 " but the log file is still empty

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  • MSTest/NUnit Writing BDD style "Given, When, Then" tests

    - by Charlie
    I have been using MSpec to write my unit tests and really prefer the BDD style, I think it's a lot more readable. I'm now using Silverlight which MSpec doesn't support so I'm having to use MSTest but would still like to maintain a BDD style so am trying to work out a way to do this. Just to explain what I'm trying to acheive, here's how I'd write an MSpec test [Subject(typeof(Calculator))] public class when_I_add_two_numbers : with_calculator { Establish context = () => this.Calculator = new Calculator(); Because I_add_2_and_4 = () => this.Calculator.Add(2).Add(4); It should_display_6 = () => this.Calculator.Result.ShouldEqual(6); } public class with_calculator { protected static Calculator; } So with MSTest I would try to write the test like this (although you can see it won't work because I've put in 2 TestInitialize attributes, but you get what I'm trying to do..) [TestClass] public class when_I_add_two_numbers : with_calculator { [TestInitialize] public void GivenIHaveACalculator() { this.Calculator = new Calculator(); } [TestInitialize] public void WhenIAdd2And4() { this.Calculator.Add(2).Add(4); } [TestMethod] public void ThenItShouldDisplay6() { this.Calculator.Result.ShouldEqual(6); } } public class with_calculator { protected Calculator Calculator {get;set;} } Can anyone come up with some more elegant suggestions to write tests in this way with MSTest? Thanks

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  • What is the most EVIL code you have ever seen in a production enterprise environment?

    - by Registered User
    What is the most evil or dangerous code fragment you have ever seen in a production environment at a company? I've never encountered production code that I would consider to be deliberately malicious and evil, so I'm quite curious to see what others have found. The most dangerous code I have ever seen was a stored procedure two linked-servers away from our core production database server. The stored procedure accepted any NVARCHAR(8000) parameter and executed the parameter on the target production server via an double-jump sp_executeSQL command. That is to say, the sp_executeSQL command executed another sp_executeSQL command in order to jump two linked servers. Oh, and the linked server account had sysadmin rights on the target production server.

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  • Parent child class relationship design pattern

    - by Jeremy
    I have a class which has a list of child items. Is there a design pattern I can copy that I can apply to these classes so that I can access the parent instance from the child, and it enforces rules such as not being able to add the child to multiple parents, etc?

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