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• Messaging pattern question

  - by Al Bundy

  Process A is calculating values for objects a1, a2, a3 etc. and is sending results to the middleware queue (RabbitMQ). Consumers read the queue and process these results further. Periodically process A has to send a snapshot of these values, so consumers could do some other calculations. Values for these objects might change independently. The queue might look like this a1, a1, a2, a1, a2, a2, a3... Consumers process each item in the queue. The snapshot has to contain all objects and consumers will process this message for all objects in one go. So the requirement is to have a queue like this: a1, a1, a3, a2, a2, [snapshot, a1, a2, a3], a3, a1 ... The problem is that these items are of different types: one type for objects like a1, a2 and other for a snapshot. This means that they should be processed in a diferent queues, but in that case there is a race condition: consumers might process objects before processing a snapshot. Is there any pattern to solve this (quite common) problem? We are using RabbitMQ for message queueing.

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• CSS Negative margins for positioning.

  - by Kyle Sevenoaks

  Is it ok to use negative margins for positioning? I have a lot in my current site and feel like it's not such a stable way to position things. I usually suggest to use them too. For example I have a checkout page with three divs on top of each other <div class="A"> header </div> <div class="B"> content </div> <div class="C"> footer </div> (A, B and C), which are meant to sit on top of each other, to appear attached. I did this using: .B { margin-top: -20px; } On div B, to meet the bottom of div A. Is this good practice or shall I re-code using top and left?

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• What to do of exceptions when implementing java.lang.Iterator

  - by Vincent Robert

  The java.lang.Iterator interface has 3 methods: hasNext, next and remove. In order to implement a read-only iterator, you have to provide an implementation for 2 of those: hasNext and next. My problem is that these methods does not declare any exceptions. So if my code inside the iteration process declares exceptions, I must enclose my iteration code inside a try/catch block. My current policy has been to rethrow the exception enclosed in a RuntimeException. But this has issues because the checked exceptions are lost and the client code no longer can catch those exceptions explicitly. How can I work around this limitation in the Iterator class? Here is a sample code for clarity: class MyIterator implements Iterator { @Override public boolean hasNext() { try { return implementation.testForNext(); } catch ( SomethingBadException e ) { throw new RuntimeException(e); } } @Override public boolean next() { try { return implementation.getNext(); } catch ( SomethingBadException e ) { throw new RuntimeException(e); } } ... }

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• Why are mutable structs evil?

  - by divo

  Following the discussions here on SO I already read several times the remark that mutable structs are evil (like in the answer to this question). What's the actual problem with mutability and structs?

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• What is the best approach to binding commands in a ViewModel to elements in the View?

  - by Micah

  Anyone who has tried to implement RoutedCommands in WPF using M-V-VM has undoubtedly run into issues. Commands (non-UI commands that is) should be implemented in the ViewModel. For instance if I needed to save a CustomerViewModel then I would implement that as a command directly on my CustomerViewModel. However if I wanted to pop up a window to show the users addresses I would implement a ShowCustomerAddress command directly in the view since this a UI specific function. How do I define the command bindings in the viewmodel, and use them in the view?

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• How to exit an if clause

  - by Roman Stolper

  What sorts of methods exist for prematurely exiting an if clause? There are times when I'm writing code and want to put a break statement inside of an if clause, only to remember that those can only be used for loops. Lets take the following code as an example: if some_condition: ... if condition_a: # do something # and then exit the outer if block ... if condition_b: # do something # and then exit the outer if block # more code here I can think of one way to do this: assuming the exit cases happen within nested if statements, wrap the remaining code in a big else block. Example: if some_condition: ... if condition_a: # do something # and then exit the outer if block else: ... if condition_b: # do something # and then exit the outer if block else: # more code here The problem with this is that more exit locations mean more nesting/indented code. Alternatively, I could write my code to have the if clauses be as small as possible and not require any exits. Does anyone know of a good/better way to exit an if clause? If there are any associated else-if and else clauses, I figure that exiting would skip over them.

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• Extending Throwable in Java

  - by polygenelubricants

  Java lets you create an entirely new subtype of Throwable, e.g: public class FlyingPig extends Throwable { ... } Now, very rarely, I may do something like this: throw new FlyingPig("Oink!"); and of course elsewhere: try { ... } catch (FlyingPig porky) { ... } My questions are: Is this a bad idea? And if so, why? What could've been done to prevent this subtyping if it is a bad idea? Since it's not preventable (as far as I know), what catastrophies could result? If this isn't such a bad idea, why not? How can you make something useful out of the fact that you can extends Throwable?

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• Ideal way to cancel an executing AsnycTask

  - by Samuh

  I am running remote audio-file-fetching and audio file playback operations in a background thread using AsnycTask. A Cancellable progress bar is shown for the time the fetch operation runs. I want to cancel/abort the AsnycTask run when the user cancels(decides against) the operation. What is the ideal way to handle such a case? Thanks.

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• How to Manage CSS Explosion

  - by Jason

  I have been heavily relying on CSS for a website that I am working on (currently, everything is done as property values within each tag on the website and I'm trying to get away from that to make updates significantly easier). The problem I am running into, is I'm starting to get a bit of "CSS explosion" going on. It is becoming difficult for me to decide how to best organize and abstract data within the CSS file. For example: I am using a large number of div tags within the website (previously it was completely tables based). So I'm starting to get a lot of CSS that looks like this... div.title { background-color: Blue; color: White; text-align: center; } div.footer { /* Stuff Here */ } div.body { /* Stuff Here */ } etc. It's not too bad yet, but since I am learning here, I was wondering if recommendations could be made on how best to organize the various parts of a CSS file. What I don't want to get to is where I have a separate CSS attribute for every single thing on my website (which I have seen happen), and I always want the CSS file to be fairly intuitive. (P.S. I do realize this is a very generic, high-level question. My ultimate goal is to make it easy to use the CSS files and demonstrate their power to increase the speed of web development so other individuals that may work on this site in the future will also get into the practice of using them rather than hard-coding values everywhere.)

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• Worst gross technical knowledge gap you've seen?

  - by Bob Albright

  What's the worst technical misunderstanding you've ever seen? Worst abuse of a good system due to lack of knowledge?

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• Format for storing contacts in a database

  - by Gart

  I'm thinking of the best way to store personal contacts in a database for a business application. The traditional and straightforward approach would be to create a table with columns for each element, i.e. Name, Telephone Number, Job title, Address, etc... However, there are known industry standards for this kind of data, like for example vCard, or hCard, or vCard-RDF/XML or even Windows Contacts XML Schema. Utilizing an standard format would offer some benefits, like inter-operablilty with other systems. But how can I decide which method to use? The requirements are mainly to store the data. Search and ordering queries are highly unlikely but possible. The volume of the data is 100,000 records at maximum. My database engine supports native XML columns. I have been thinking to use some XML-based format to store the personal contacts. Then it will be possible to utilize XML indexes on this data, if searching and ordering is needed. Is this a good approach? Which contacts format and schema would you recommend for this?

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• Time/resource allocation on a Stylish vs. Functional user interface

  - by jasonk

  When developing applications how much focus/time do you place on an application’s style vs. functionality. Battleship gray apps drive me insane. On the other hand maximizing a business application’s "style" can tax time and financial resources. Applications need to be appealing to resell or meet basic customer expectations, but defining a healthy medium can be difficult. What would you say are reasonable "standards" for allocating develop time/resources should be dedicated to stylizing a business application?

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• How do you handle very old browsers on your site?

  - by Alex

  Hi. We have a non-profit web site that got about 5 million hits in May. Of those, about 5,700 were from IE 5.x or lower; about 4,000 were from folks with Netscape 4.x or lower. We know that the current site's layout works for newer browsers and we're testing it on IE6 as well (along with Chrome, Opera, Safari, and Firefox). How do you handle the folks with the older browsers? Because of jQuery libraries and such, the pages might not function correctly on those old browsers. Is there an easy way to show a text-only version on browsers that can't handle the CSS and jQuery goodies? How do large sites handle this sort of thing? I've used the @embed to hide the stylesheet from Netscape 4.x, but not sure beyond that.

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• Annoying things accepted as standard practice

  - by Aram Havarneanu

  What things that are considered standard practice, you think have no inherent value and annoy you? For example, in C++, Java, C# and similar OOP languages, I find prefixing class fields like m_var or _var completely useless and hard on the eyes.

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• Is "34KB" or "34 KB" more correct?

  - by jitendra

  When I am displaying a file size to a user, is "34KB" or "34 KB" more correct?

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• logic of button to be disabled or not in mvc

  - by rod

  Hi All, Here's an excerpt from a book I'm reading about application design with MVC: Ideally, the view is so simple and logic-free as to need virtually no testing. Users (and developers before users) can reasonably test the view by simply looking at the pixels on the screen. Anything else beyond pure graphical rendering should ideally be taken out of the view and placed in the controller and model. This includes, for example, the logic that determines whether a certain button should be enabled or grayed out at some point. what does the bold statement mean to you? what would this look like? thanks, rod.

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• Pattern for managing reference count and object life

  - by Gopalakrishnan Subramani

  We have a serial port which is connected to hundreds of physical devices on the same wire. We have protocols like Modbus and Hart to handle the request and response between the application and devices. The question is related to managing the reference count of the channel. When no device is using the channel, the channel should be closed. public class SerialPortChannel { int refCount = 0; public void AddReference() { refCount++; } public void ReleaseReference() { refCount--; if (refCount <= 0) this.ReleasePort(); //This close the serial port } } For each device connected, we create a object for the device like device = new Device(); device.Attach(channel); //this calls channel.AddReference() When the device disconnect, device.Detach(channel); //this calls channel.ReleaseReference() I am not convinced by the reference count model. Are there any better way to handle this problem in .NET World?

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• Asp.Net MVC2 TekPub Starter Site methodology question

  - by Pino

  Ok I've just ran into this and I was only supposed to be checking my emails however I've ended up watching this (and not far off subscribing to TekPub). http://tekpub.com/production/starter Now these app is a great starting point, but it raises one issue for me and the development process I've been shown to follow (rightly or wrongly). There is no conversion from the LinqToSql object when passing data to the view. Are there any negitives to this? The main one I can see is with validation, does this cause issues when using MVC's built in validation as this is somthing we use extensivly. Because we are using the built in objects generated by LinqToSql how would one go about adding validation, like [Required(ErrorMessage="Name is Required")] public string Name {get;set;} Interested to understand the benifits of this methodology and any negitives that, should we take it on, experiance through the development process.

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• Email as a view.

  - by Hal

  I've been in some discussion recently about where email (notifications, etc...) should be sent in an ASP.NET MVC application. My nemesis grin argues that it only makes sense that the email should be sent from the controller. I argue that an email is simply an alternate or augmented view through a different channel. Much like I would download a file as the payload of an ActionResult, the email is simply delivered through a different protocol. I've worked an extension method that allows me to do the following: <% Html.RenderEmail(model.FromAddress, model.ToAddress, model.Subject); %> which I actually include within my the view that is displayed on the screen. The beauty is that, based on convention, if I call RenderEmail from a parent view named MyView.ascx, I attempt to render the contents of a view named MyViewEmail.ascx, unless it is not found, in which case I simply email a copy of parent view. It certainly does make it testable (I still have an ISMTPService injected for testing), I wondered if anyone had any thoughts on whether or not this breaks from good practice. In use it has been extremely handy when we needed to easily send an email or modify the contents of the emailed results vs the browser rendered results. Thanks, Hal

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• How to restrain one's self from the overwhelming urge to rewrite everything?

  - by Scott Saad

  Setup Have you ever had the experience of going into a piece of code to make a seemingly simple change and then realizing that you've just stepped into a wasteland that deserves some serious attention? This usually gets followed up with an official FREAK OUT moment, where the overwhelming feeling of rewriting everything in sight starts to creep up. It's important to note that this bad code does not necessarily come from others as it may indeed be something we've written or contributed to in the past. Problem It's obvious that there is some serious code rot, horrible architecture, etc. that needs to be dealt with. The real problem, as it relates to this question, is that it's not the right time to rewrite the code. There could be many reasons for this: Currently in the middle of a release cycle, therefore any changes should be minimal. It's 2:00 AM in the morning, and the brain is starting to shut down. It could have seemingly adverse affects on the schedule. The rabbit hole could go much deeper than our eyes are able to see at this time. etc... Question So how should we balance the duty of continuously improving the code, while also being a responsible developer? How do we refrain from contributing to the broken window theory, while also being aware of actions and the potential recklessness they may cause? Update Great answers! For the most part, there seems to be two schools of thought: Don't resist the urge as it's a good one to have. Don't give in to the temptation as it will burn you to the ground. It would be interesting to know if more people feel any balance exists.

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• Is a "factory" method the right pattern?

  - by jdt141

  Hey all - So I'm working to improve an existing implementation. I have a number of polymorphic classes that are all composed into a higher level container class. The problem I'm dealing with at the moment is that the higher level container class, well, sucks. It looks something like this, which I really don't have a problem with (as the polymorphic classes in the container should be public). My real issue is the constructor... /* * class1 and class 2 derive from the same superclass */ class Container { public: boost::shared_ptr<ComposedClass1> class1; boost::shared_ptr<ComposedClass2> class2; private: ... } /* * Constructor - builds the objects that we need in this container. */ Container::Container(some params) { class1.reset(new ComposedClass1(...)); class2.reset(new ComposedClass2(...)); } What I really need is to make this container class more re-usable. By hard-coding up the member objects and instantiating them, it basically isn't and can only be used once. A factory is one way to build what I need (potentially by supplying a list of objects and their specific types to be created?) Other ways to get around this problem? Seems like someone should have solved it before... Thanks!

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• Best practice regarding returning from using blocks

  - by abatishchev

  Which way is better practice: return a value from a method inside an using statement or declare a variable before, set it inside and return it after? public int Foo() { using(..) { return bar; } } or public int Foo() { var b = null; using(..) { b = bar; } return b; }

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• Using DTOs and BOs

  - by ryanzec

  One area of question for me about DTOs/BOs is about when to pass/return the DTOs and when to pass/return the BOs. My gut reaction tells me to always map NHibernate to the DTOs, not BOs, and always pass/return the DTOs. Then whenever I needed to perform business logic, I would convert my DTO into a BO. The way I would do this is that my BO would have a have a constructor that takes a parameter that is the type of my interface (that defines the required fields/properties) that both my DTO and BO implement as the only argument. Then I would be able to create my BO by passing it the DTO in the constructor (since both with implement the same interface, they both with have the same properties) and then be able to perform my business logic with that BO. I would then also have a way to convert a BO to a DTO. However, I have also seen where people seem to only work with BOs and only work with DTOs in the background where to the user, it looks like there are no DTOs. What benefits/downfalls are there with this architecture vs always using BO's? Should I always being passing/returning either DTOs or BOs or mix and match (seems like mixing and matching could get confusing)?

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• ASP.NET MVC null ViewResult

  - by David Neale

  How should one deal with an MVC controller returning a null ViewResult? As an example I am creating a simple edit view: public ActionResult Edit(int id) { var person = (from p in context.SWLiftShare_Persons where p.id == id select p).SingleOrDefault(); if (person != null) { return View(person); } else return View(); } I guess in reality there's no point in checking for a null result in the controller because the view picks out properties from the model: <h2>Edit - <%= Html.Encode(Model.Name) %></h2> <%= Html.ValidationSummary("Edit was unsuccessful. Please correct the errors and try again.") %> <% using (Html.BeginForm()) {%> <fieldset> <legend>Fields</legend> <p> <label for="id">id: <%= Html.Encode(Model.id) %></label> </p> <p> <label for="CollarNumber">CollarNumber:</label> <%= Html.TextBox("CollarNumber", Model.CollarNumber)%> <%= Html.ValidationMessage("CollarNumber", "*") %> </p> <p> <label for="Name">Name:</label> <%= Html.TextBox("Name", Model.Name)%> <%= Html.ValidationMessage("Name", "*") %> </p> <p> <label for="EmailAddress">EmailAddress:</label> <%= Html.TextBox("EmailAddress", Model.EmailAddress, new { style = "width:300px" })%> <%= Html.ValidationMessage("EmailAddress", "*") %> </p> <p> <input type="submit" value="Save" /> </p> </fieldset> <% } %> I could just wrap everything in a <% if(Model != null) { //render edit markup... etc. but that seems rather unelegant. Is there a better way to deal with this?

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• Best practice - When to evaluate conditionals of function execution

  - by Tesserex

  If I have a function called from a few places, and it requires some condition to be met for anything it does to execute, where should that condition be checked? In my case, it's for drawing - if the mouse button is held down, then execute the drawing logic (this is being done in the mouse movement handler for when you drag.) Option one says put it in the function so that it's guaranteed to be checked. Abstracted, if you will. public function Foo() { DoThing(); } private function DoThing() { if (!condition) return; // do stuff } The problem I have with this is that when reading the code of Foo, which may be far away from DoThing, it looks like a bug. The first thought is that the condition isn't being checked. Option two, then, is to check before calling. public function Foo() { if (condition) DoThing(); } This reads better, but now you have to worry about checking from everywhere you call it. Option three is to rename the function to be more descriptive. public function Foo() { DoThingOnlyIfCondition(); } private function DoThingOnlyIfCondition() { if (!condition) return; // do stuff } Is this the "correct" solution? Or is this going a bit too far? I feel like if everything were like this function names would start to duplicate their code. About this being subjective: of course it is, and there may not be a right answer, but I think it's still perfectly at home here. Getting advice from better programmers than I is the second best way to learn. Subjective questions are exactly the kind of thing Google can't answer.

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