Tag: c#

Posted on

Generics in Java and C#

Today I was writing some interceptors in Java, and I wanted to be able to filter the input based on whether it implemented a given interface or otherwise. Class<?> exposes a very handy isAssignableFrom method for this, but it doesn’t look very nice, so I tried to go for something a bit neater, like: 

   1: Feature.<TargetFeature>isImplementedBy(interceptedInstance);

Neat, and much more readable. I didn’t quite make it there, but got close enough for my purposes, and had some (very little) deeper knowledge of generics inflicted upon me for my sins.

Continue reading “Generics in Java and C#”

Posted on

Behaviour driven development on user interfaces with Automation peer

Testing user interfaces is usually a pain in the butt. No matter how cool your UI is, it will often boil down to a brain-cell killing process clicking the same buttons over and over again. Thanks to the Geek Gods of .Net though, there are ways to automate this, and it’s not even that tough to do.

In this post, we’re going to use Automation peers to expose a button to a unit test, and have the test start the application, click the button, and confirm that the button does what it’s meant to do. We’re going to use MbUnit to write the test, and NBehave to make the tests nice and clear.

Continue reading “Behaviour driven development on user interfaces with Automation peer”

Posted on

Is this thing on?

Download sample code here (New window)

There’s been a project knocking around the back of my head for a while. I keep putting it off, doing some work on it now and again but never really settling down to really do it. This long weekend turned out to be one of those occasions; I’ve just finished playing Fallout 3 (Awesome game, the ending left a slightly bitter taste in my mouth though) and ended up with nothing to do. Visual Studio to the rescue…

Now what?

If you ever worked on an application that requires Internet connectivity, you will have had to handle situations where the connection may be unavailable for certain periods of time. Sometimes you can get by that by trapping an exception; I know I have, though I still find that particular solution to be somewhat inelegant. What I wanted was some way to monitor the state of the connection and keep track of it. This way, if you need to send a message for example, you can have your application decide whether it should try to send it right away, or whether it should stash it away till the connection becomes available. This post is about how to determine whether a connection is up or down, and notify the application when the state changes. Continue reading “Is this thing on?”

Posted on

Dynamic proxies using Castle

The sample code can be downloaded here

This week I found myself with some time on my hands, so I knocked up a simple object pool. It’s fairly standard stuff… you call Fetch to get something out of the pool, and Return to put it back. Fairly standard.

The problem

The call to Return felt a bit annoying. If we forget to call that, we end up leaking resources as we create more and more objects, or get an exception thrown at us. Not good. I wanted something like the using (whatever) syntax, which I think is the most awsome thing ever.

To do that, we’d have to ensure that all the items in the pool implement IDisposable, have a reference back to the pool, and call Return in their dispose method. This isn’t really feasible; for starters, it would tightly couple everything with the pool, which is, like, all sorts of bad. A far better approach is, in my opinion, to wrap the object being pooled to add whatever behaviour I need. Not necessarily a great idea if you don’t know what’s going to be pooled beforehand. Continue reading “Dynamic proxies using Castle”

Posted on

Yet another carousel control

Download the control here

I meant to write something about MEF after my holiday, but I’ve been sidetracked
for a while. One of the things that happened to divert my notoriously unstable attention was a quite excellent five day Blend course by Brennon Williams. My preferred method of writing XAML has been, so far, in a text editor, but Herr Williams was quite persuasive in demonstrating that Blend is, in fact, far, far better for the job.

As part of the course, we wrote a small application. I ended up hacking together a 3d carousel user control for this, which I felt was pretty cool, so I set about rewriting it as a custom control for future use. No, I did
not use Blend. Yes, I did notice it’s a damn sight harder to do it in pure code than it was in Blend.

Warning: This post contains some math. Continue reading “Yet another carousel control”

Posted on

A File Organizer

If you’re anything like me, you probably have a few thousand documents and files lurking around a small forest of New Folder(n) on your desktop. If you’re anything like me at all, you probably also lack the time, interest, inclination and attention span needed to track them down, go through them, and organize them. Now, it so happened that some time ago, a friend of mine had complained of being in a similar situation; worse in fact, since more than one person uses her PC, leaving the whole thing in a mush.

It so happened that I didn’t have much to do in the weekend (note to self: get a life. Naaah…), and had been wanting to brush up a bit on WPF for quite some time, so I sat myself down and started coding. The result is this organizer. Continue reading “A File Organizer”

Posted on

Validating attribute usage with PostSharp Aspects

This post expands on my previous article on PostSharp. If you haven’t already, read it here.

Most of January has flown by with just one post, effectively shooting down my resolution to blog more often. In my defence, I have to state that I’ve just moved on to newer pastures, with all the re-settling in that involves.

Apart from that, I also spent a few hours twiddling with the Jasema sources, so I do have something to post about at least. 🙂

The .net attribute architecture supports an Attribute Usage definition, which is itself an attribute that can be applied to attributes. AttributeUsageAttribute determines whether said attribute can be applied to fields, methods, classes, assemblies, or any combination thereof. This allows you to identify, at compilation time, whether the attributes you have specified are used correctly, which is great.

There are situations, however, where you might want to enforce some more detailed constraints on an attribute; for example, you might want to make sure that it is only used by classes that implement a given interface, or check what parameters have been defined for it.

It is possible to implement this as a runtime check within the attribute itself, however this is not always a very elegant solution. If you check the constraints every time the attribute is invoked in some way, you’re incurring a performance hit, however slight. If one considers that PostSharp aspects may be called every time data changes in a given field, or every time a method (or even any method in an assembly is called), this may add up to quite a bit, depending on what sort of checking you’re doing.

By making this sort of check at run time, you’re also depriving yourself of compile time checking. Even if you have unit tests in place to make sure you catch incorrect behaviour. it can still take time to run the suite; wouldn’t it be a lot nicer if the compiler could be instructed to raise an error when an attribute is given the wrong parameters, or is used with the wrong sort of class?

While PostSharp aspects don’t allow you to give such instructions to the compiler, they do allow you to do something that’s so similar that the difference, to someone like me, is purely academic (so, flame me). These aspects define an OnCompileValidate method, which can be overridden in your custom aspects. Continue reading “Validating attribute usage with PostSharp Aspects”

Posted on

Writing a Custom Appender for log4net

On most of my projects, I use log4net (a habit I carried over from Java really) to maintain traces and logs. I find it preferable to using the trace mechanism, and it certainly beats Console.Write as a technique. One of the best things about it is that you can configure appenders to write to pretty much anything. The appenders that come bundled with log4net cover most of the stuff you’d actually want to log to – the event logs, console, a database, file system, and so on. However, sometimes you may need something a little more specific.

In my case, I needed to have one of my projects log issues directly into the issue tracking system we use here. Said tracking system exposes a web service to do just that, so I set about writing an appender that would consume this service. I’m not going to go into the details of how to connect to this specific system, but hopefully this short post will illustrate how incredibly easy it is to write a custom appender. Continue reading “Writing a Custom Appender for log4net”

Posted on

LuaInterface

While having a beer with an old friend yesterday, we started discussing the use of scripting languages in applications. Having seen a number of .net applications with embedded Lua scripting engines, I suggested that he look at LuaInterface, with the disclaimer that I hadn’t used it much myself.

Having nothing better to do this afternoon, I decided to download the whole thing again (the last version I’d downloaded had languishing in my download folder for about 10 months, and was probably out of date, if I could find it in the first place) and have a go at it. Attached are the results of my messing around. It’s by no means a best practice guide – or even a good practice guide, for that matter – but it looks like it’s working. Continue reading “LuaInterface”