Testing file existence using NSURL

Solution 1:

NSURL does have this method:

- (BOOL)checkResourceIsReachableAndReturnError:(NSError **)error

Which "Returns whether the resource pointed to by a file URL can be reached."

NSURL *theURL = [NSURL fileURLWithPath:@"/Users/elisevanlooij/nonexistingfile.php" 
               isDirectory:NO];
NSError *err;
if ([theURL checkResourceIsReachableAndReturnError:&err] == NO)
    [[NSAlert alertWithError:err] runModal];

Solution 2:

On iOS I couldn't find any other way...

NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"file.type"];
if ([[NSFileManager defaultManager] fileExistsAtPath:[storeURL path]]) {...}

Solution 3:

Here is the Swift 2 answer:

var error:NSError?
let folderExists = theURL.checkResourceIsReachableAndReturnError(&error)

Solution 4:

Determining if a given file (or file-reference) URL refers to a file-system object that exists is inherently costly for remote resources, the 10.6 only (no iPhoneOS) api's for this CFURLResourceIsReachable() and [NSURL checkResourceIsReachableAndReturnError:] are both synchronous, even if you would be using them, for a lot of files you would still be looking at a significant delay overhead.

What you should do is implement your own asynchronous checking routine with caching that separately creates a list of valid resources.

Otherwise the notes for CFURLResourceIsReachable in the header state :

An example would be periodic maintenance of UI state that depends on the existence of a particular document. When performing an operation such as opening a file, it is more efficient to simply try the operation and handle failures than to check first for reachability.