Tag Archives: cocoa

Dealing with .csv files in Cocoa – writing an importer

Mac users who need to deal with large amounts of data might justifiably feel like they got the short end of the stick as far as Microsoft Office is concerned. The Mac version of Excel doesn’t support Visual Basic and isn’t multithreaded, meaning that:

a) as soon as you get above a couple of tens of thousands of rows, any formula more complicated than summing a column freezes the UI for a couple of minutes while it crunches the numbers, and

b) any data analysis you want to do which involves iteration results in formulae consisting of ten lines of densely nested brackets, which are nearly impossible to read or debug.

Like any bad programmer, I implicitly believe that my language of choice is the perfect tool for any job, and hence when recently confronted with a very large stack of data I needed to analyse I decided it would be easiest to Object Oriented the hell out of it with a small custom C application.

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NSDocument saving quirks

Let’s say you have a document-based application which worked fine under Leopard/Snow Leopard.  Each document is backed by an XML store, and hence the saving method works by exporting the contents of a number of NSTextViews into one string of XML, which is saved to disk.  You’ve been happily overriding

- (BOOL)saveToURL:(NSURL *)url ofType:(NSString *)typeName forSaveOperation:(NSSaveOperationType)saveOperation error:(NSError **)outError

as being a sensible point to insert your custom document-saving code – in my case, I send the NSString which holds all of the document’s data to a basic XML exporter, which does clever stuff like removing all of the illegal characters, etc.  You then use NSString’s writeToURL: atomically:encoding:error method to do the actual write.  This works fine pre-Lion.

Everything goes swimmingly until you upgrade to Lion/Mountain Lion and try to save the document in place (i.e. save rather than save as:).  Your application pops up a warning sheet saying “This document’s file has been changed by another application since you opened or saved it.

Every.  Single.  Time.

Workaround: give your application a file wrapper so that you can add some metadata, and you can trick your application into realising that the file hasn’t been altered after all. You can do this by overriding NSDocument’s fileWrapperOfType: method rather than saveToURL. This is from an application for writing questions and answers to an XML file which is then used as the data source for a quiz application, hence the funny QuestionExporter/setQuizDocument object and setter:

- (NSFileWrapper *)fileWrapperOfType:(NSString *)typeName error:(NSError *__autoreleasing *)outError {
    QuestionExporter *exporter = [[QuestionExporter alloc]init];
    [exporter setQuizDocument:self];
    NSString *xmlString = [exporter exportQuestionsToString];
    NSFileWrapper *wrapper = [[NSFileWrapper alloc]initRegularFileWithContents:[xmlString dataUsingEncoding:NSUTF8StringEncoding]];
    return wrapper;
}

Hello world!

Those (few) of us who got our start in graphics coding in OS X have probably noticed a few wrinkles in the process:

  • Apple’s OpenGL/GLSL implementation is always a year or two out of date
  • OpenGL tutorials on the internet are always 5 years out of date, and actually written for DirectX anyway
  • Books on the subject cost £50 for a hard-to-search collection of stuff you already knew which is inevitably dependant on some library or other (which they don’t explain) to do all of the magic
  • GLSL is, as Shamus Young so rightly pointed out, folk knowledge
  • As soon as you want to interact with OpenGL, you have to leave your cosy Cocoa haven and delve into straight C – which is moon language to those of us raised on NSExtremelyVerboseFunctionNameWithAttributes:

Hence I’ve made this site to put up some of the more obscure – or so obvious nobody has ever bothered to put up a working implementation for us newbies to pore over – code which took me hours of googling to figure out.  It’s so much easier to learm by breaking a working implementation than to mess about with something originally written in a different language which might not even work in the first place.

In the process, I’m going to build one of those procedural environment things.  This was going to be a simple 2D Artificial Stupidity project, but the graphics sort of took over.

There will be bugs.  There will definitely be memory leaks.  Much of this stuff will be apocryphal, or at least wildly inaccurate.  Your video card will probably crash at some point, and I’m definitely not going to buy you a new one.

Enjoy!