In one of my recent projects, the need to encode QR codes on the device came up. I tried a few different methods and wasn't really satisfied with any of them. The method detailed here is the one I chose based on ease of use and the quick set up time. The core library is written in c and the base version can be found here: http://fukuchi.org/works/qrencode/index.html.en (download the entire project below).

I am using a modified version with a few helper methods written in objective-c. Then my usage is as follows:

{% highlight objc %} UIImage *image = [self quickResponseImageForString:@"http://danielbeard.wordpress.com" withDimension:182];

//set the image
[imageView setImage: image];

{% endhighlight %}

And the result: Image

Here is the full project with an example: Download Project