I thought I should broaden my C# knowledge a bit and you know how it is: To learn new stuff you need a real project to work on or else you will lose the fire sooner than later. So I came up with a good project that is actually useful to me: Porting Roxen’s “Application Launcher” to C#. There’s nothing wrong with the original one, written in Pike, except that it uses GTK 1 which is quite hideous (in an aesthetic meaning) compared to the newer GTK 2. And I also though it would be cool to create a panel applet (in the notification area of Gnome so you could put the Application Launcher in the background).
BTW: For those of you not knowing what the heck Roxen’s Application Launcher (AL here after) is here’s a brief explanation: Files in Roxen CMS is stored in a CVS file system which means that you don’t deal with files the way you normally do. To manage files you use a web browser interface (which is a darn good one I might add) but sometimes you actually want to edit files in your standard desktop application. And it is here the AL comes to play. You can download a file through the browser interface so that the file is opened in the AL. AL will then open the file in the desktop application you have associated with the file’s content-type. When you make your changes and saves them the AL will directly upload the changes to the server. So in short I could have said: The Application Launcher is a means to edit files on a remote Roxen server with a preferred desktop application.
I must say I’ve learned a lot from this project!
First off: If you download a file for editing and the AL is already started you don’t want to start a new instance of AL (this is something I have never ever thought about before – in general terms, not just concerning AL) but when you do think about it you find that it’s not a piece of cake to solve. I solved it the way it is solved in the original AL. The first instance of AL that is started also starts a “socket server” that listens for incoming traffic on a given port on the local IP. When a new instance is started it first checks if it can connect to said port and if it can it sends the arguments through the socket to the first instance which then handles the request. The second instance is simply terminated when it has send the data though the socket.
So there I had to do some socket programming. Great fun
Secondly: Stuff happens in the background of AL – data send through the socket remember – which means that nothing happens when you try to update the Graphical User Interface. (NOTE! This is the first more advanced desktop application I’ve done.) After “Google-ing” around a bit I came to know that this was a real newbie problem The thing is that the GUI can only be updated through the same thread that started it so when using background threads – implicitly that’s what I’m doing although handled by the asynchronous callback infrastructure of C# – you need to make sure the GUI is updated through the main thread. This is the most simple way so solve it:
That’s not too difficult when you know it
Thirdly: The AL is sending data back and forth through the HTTP protocol which means we have to use some sort of HTTP client. C# has a couple of ways to do this but unfortunately they came up short, or I couldn’t use them anyway. I didn’t manage to figure out exactly why I always caught an exception saying something like: A protocol violation occurred!. I’m far from the only one who have fought with this and it has something to do with the headers sent from the remote server. You can invoke “unsafe header parsing” but that was to much of a hassle so I created my own little HTTP client.
One big annoying thing with C# is that is seems almost impossible to turn data from streams into strings without having to use any one of the
System.Text.Encoding.* classes/objects which in my case meant that images and files in binary form got seriously fucked up. I manged to solve this my never turning the data into a string but keeping it as a
System.Text.Encoding.* all the way from request to response to saving to disk. It was rather irritating but at the same time nice when solved (and I learned a whole bunch about
Finally: Of course I learned a great deal more about C# but this blog post is starting to get pretty excessive so I will round it off by saying that MonoDevelop is starting to become pretty darn good! I just upgraded to the latest version of Ubuntu and that also meant that I got the latest MonoDevelop and I must say it’s more stable than ever (although it occasionally crashes) and a whole bunch of new features are in place. One I havn’t used before – although it might have existed before – is the “Deployment” stuff. It creates a package with configure and make files for optimal compilation. Really smooth!
Source and screens
I will finish off by adding the source files and a few screen shots:
Roxen Application Launcher 17:31, Sat 17 October 2009 :: 96.7 kB
Screen shot 1: Just a standard view
Screen shot 2: The panel applet in action
Screen shot 3: The Application Launcher in Swedish
Screen shot 4: Adding support for a new content type