Modding Mac OS X

Building Bundles

In terms of display, naming is everything. The Finder is responsible for selecting the way a directory appears: as a normal folder, as a file, or as an application. A file’s name, particularly its underlying file extension (.app), tells the Finder which kind of presentation to use. Here’s a quick-and-dirty way to test this behavior out for yourself.

1. In the Finder, choose File → New Folder (Shift-⌘-N). Give the folder a simple name (e.g., Chuck), as shown in Figure 2-3.

   

   Figure 2-3. A normal Mac OS X folder.

2. Add a file to the folder, so that there’s at least one item inside.

3. Single-click on the folder’s name; the name will be highlighted in light blue. Hit the Right Arrow (or Down Arrow) key to move the cursor to the end of the folder’s name, and then add a .bundle extension to the folder (e.g., Chuck.bundle). Finder accepts the update and changes to use a generic file icon, as shown in Figure 2-4.

   

   Figure 2-4. A folder using a .bundle extension looks like a single document.

4. Select the folder and choose File → Open (or double-click the renamed icon). An alert appears, telling you that there’s no default application specified to open your “document”

At this point, you can still open the renamed folder by Control-clicking on the icon and choosing Show Package Contents from the ...