I just submitted iDjembe 2.0 to the app store. I decided to change the version number to 2.0 because I did a major rewrite of the audio player code.

For the first version, I just wanted to make something quick that hopefully would cash in on the app craze and make some money. This time I’m serious about making it good.

The major new feature is Virtual Drum Circle, which lets you connect to other players on the local network and broadcast your beats to them.

The major under the hood change is that it now uses OpenAL instead of the simple audio player (which pretty much sucked). I tried several sound APIs including Audio Queue and AVAudioPlayer, but I found that OpenAL is the most straightforward and gives the best performance.

Unfortunately Apple’s iPhone developer documentation doesn’t cover OpenAL, although there are several code samples that use it. I found the best information to be at Ben Britten’s blog and the official OpenAL site.

After some experimentation, I determined the best strategy is to use a pool of OpenAL sources and prepare a buffer for each sound. Instead of using a single source for each sound, when I need to play a sound, I get the next available source, and add the desired sound buffer to it. As a result, it can now play more than one sound at a time and can play the same one repeatedly without a click.

My iPhone development signing certificate expired yesterday. Thankfully I found that creating a new certificate is quick and painless. Luckily I still have my Certificate Signing Request (CSR).

All you really have to do is upload the CSR. If you don’t have it, you’ll have to create a new one by following the instructions in the certificates tab in ADC’s iPhone center.

After uploading the CSR, you’ll have to approve it by clicking the ‘approve’ button in the certificates tab. In a few minutes, the certificate is ready to download.

Thanks to Craig Hockenberry for pointing out that iPhone developer & distribution certificates are beginning to expire. I checked my keychain and found that my developer certificate expires tomorrow and my distribution certificate expires on the 25th. I’m not sure if I still have my original certificate signing request (CSR), so I’ll probably have more work to do.

For any other iPhone developers reading this, open Keychain Access, do a search for ‘iPhone’ and note the expiration dates. Don’t be caught by surprise.

One of the changes I’m making in the next version of ICanHasCheezburger is improved multi-touch handling. In the current version, I’m only handling left & right swipes to switch to the previous or next images. For the update, I’d like to handle the same gestures as the photo app:

• Pinch to zoom in & out
• When zoomed in, drag the image to see different portions
• When zoomed or moved, double-tap to return to the standard zoom
• Swipe left & right to move to the next image – but NOT when zoomed in
• Single tap to toggle toolbar & menu bar

In many cases you can use a UIScrollView, which implements most of those behaviors. For ICHC, I decided to subclass UIImageView to handle touch gestures.
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Since the F**KING NDA makes it difficult to find iPhone programming tips & sample code, I thought I’d share this little tidbit.

Sometimes the easiest way to display a help or information screen is a UIWebView. It’s very easy to display the contents of an HTML file stored in the application’s resource bundle.

    NSData *info = [NSData dataWithContentsOfFile: [[NSBundle mainBundle] pathForResource:@"info" ofType:@"html"]];
    [webView loadData:info MIMEType:@"text/html" textEncodingName:@"utf8" baseURL:nil];

However, if you have any external links, they will open in the same web view, which you probably don’t want. I found a very nice work-around to have any clicked URLs open in Safari. You’ll need to specify a delegate for your web view that implements the webView:shouldStartLoadWithRequest:navigationType method. The code is very simple.

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType
{
    if (navigationType == UIWebViewNavigationTypeLinkClicked) {
        [[UIApplication sharedApplication] openURL: [request URL]];
        return NO;
    }
    return YES;
}

Kudos to Craig Hockenberry for defying Apple’s F***ING NDA and releasing the source code for an iPhone game, Lights Out, as inspiration for aspiring iPhone developers.

TouchCode is a set of iPhone open source projects that fill in some features that are missing from Cocoa Touch. The most useful part is TouchXML, which is a drop-in replacement for Cocoa’s NSXML* classes.

I was able to get the unmodified ObjectiveFlickr code working by simply doing a global search & replace of NSXMLDocument with CXMLDocument, NSXMLNode with CXMLNode, and NSXMLElement with CXMLElement. The result is less ugly than using NSXMLParser.

For the Official LOLCats application I need to handle RSS feeds, which I found to be exceptionally ugly with NSXMLParser. With TouchXML it’s easy. I can get an array of items with something like this:


NSError *err = nil;
CXMLDocument *doc = [[CXMLDocument alloc]
initWithContentsOfURL: [NSURL URLWithString: @"http://feeds.feedburner.com/myfeed"]
options:0 error: &err];

NSArray *nodes = [doc nodesForXPath: @"//item" error: nil];