September 30 2009

Rereading Info.plist

by Brian Dunagan

Apple has a nice mechanism for storing important app bundle information outside of the application executable: Info.plist. All the applications in /Applications have one; just right-click on any app, select "Show Package Contents", then click on "Contents". The file elegantly houses many facts (version, name, copyright) about your app. And Apple has a straight-forward API to get at that data: [[NSBundle mainBundle] infoDictionary]. The call returns an NSDictionary filled with key-value pairs from the Info.plist file. This workflow allows me to easily add my own key-value pairs to the file and quickly access them in code.

Recently, I wanted to read the key-value pair dynamically. That way, the user could change the value at any time, and within a minute, the app would use the new value. This proved harder. As it turns out, Apple optimized the infoDictionary query, so that it caches the contents at startup and returns that cached version through the application lifetime. If the user modified the key-value pair, that change wouldn't show up until the next startup. Instead of using that builtin method, I had to read the Info.plist file directly. See the code below.

// [[NSBundle mainBundle] infoDictionary] is cached at app startup, so we need to read the file directly for latest data.
NSString *infoPlistFilePath = [NSString stringWithFormat:@"%@/Contents/Info.plist", [[NSBundle mainBundle] bundlePath]];
NSString *infoDictionary = [NSDictionary dictionaryWithContentsOfFile:infoPlistFilePath];
NSString *value = [infoDictionary valueForKey:@"InfoPlistKey"];

UPDATE: This is a lesson in design. While the code does function as described, I now agree that no user should be subjected to this workflow. Check out my longer explanation about the feature's design.