Cocoa in a Nutshell

Working with Files

The Foundation framework provides access to data stored in files in several ways. All of the basic data classes have methods for initializing objects from the contents of files, and for writing the data represented by the object to a file. In addition to these convenience facilities, Foundation provides two classes that provide a much higher level of interaction with files and the filesystem: NSFileManager and NSFileHandle.

The File Manager

The NSFileManager class is an interface that applications use to access and manipulate files and directories in the filesystem; instances of NSFileManager provide a doorway to the filesystem for application developers. Several of NSFileManager’s methods call for a handler: argument. The handler is an object that should implement fileManager:willProcessPath: and fileManager:shouldProceedAfterError: methods. These callback methods allow for error handling and confidence testing with respect to the operation being performed. In Example 2-26, nil is passed to handler: for the sake of clarity.

Additionally, methods that deal with movement around in the filesystem and perform operations on files and directories typically return a BOOL value, to indicate an operation’s success or failure. Finally, methods that create new files or directories usually take a dictionary with file attributes as an argument. The attributes dictionary may take values to set the file’s owner, group owner, modification date, POSIX permissions; determine whether ...