Programming iOS 6, 3rd Edition

Basic File Operations

Let’s say we intend to create folder MyFolder inside the Documents directory. Assume that we have an NSFileManager instance fm and an NSURL docsurl pointing at the Documents directory, as shown in the previous section. We can then generate a reference to MyFolder; we can then ask our NSFileManager instance to create the folder if it doesn’t exist already:

NSURL* myfolder = [docsurl URLByAppendingPathComponent:@"MyFolder"];
NSError* err = nil;
BOOL ok =
    [fm createDirectoryAtURL:myfolder
        withIntermediateDirectories:YES attributes:nil error:nil];
// ... error-checking omitted

To learn what files and folders exist within a directory, you can ask for an array of the directory’s contents:

NSError* err = nil;
NSArray* arr =
    [fm contentsOfDirectoryAtURL:docsurl
        includingPropertiesForKeys:nil options:0 error:&err];
// ... error-checking omitted
NSLog(@"%@", [arr valueForKey:@"lastPathComponent"]);
/*
MyFolder
*/

The array resulting from contentsOfDirectoryAtURL:... lists full URLs of the directory’s immediate contents; it is shallow. For a deep array, which might be very big, you can enumerate the directory, so that you are handed only one file reference at a time:

NSDirectoryEnumerator* dir =
    [fm enumeratorAtURL:docsurl
        includingPropertiesForKeys:nil options:0 errorHandler:nil];
for (NSURL* f in dir)
    if ([[f pathExtension] isEqualToString: @"txt"])
        NSLog(@"%@", [f lastPathComponent]);
/*
file1.txt
file2.txt
*/

A directory enumerator also permits you to decline to dive into ...