如何检查Cocoa和Objective-C中是否存在文件夹？

Returns a Boolean value that indicates whether a specified file exists.

- (BOOL)fileExistsAtPath:(NSString *)path isDirectory:(BOOL *)isDirectory

Parameters
path
The path of a file or directory. If path begins with a tilde (~), it must first be expanded with stringByExpandingTildeInPath, or this method will return NO.

isDirectory
Upon return, contains YES if path is a directory or if the final path element is a symbolic link that points to a directory, otherwise contains NO. If path doesn’t exist, the return value is undefined. Pass NULL if you do not need this information.

Return Value
YES if there is a file or directory at path, otherwise NO. If path specifies a symbolic link, this method traverses the link and returns YES or NO based on the existence of the file or directory at the link destination.

NSString *pathToFile = @"...";
BOOL isDir = NO;
BOOL isFile = [[NSFileManager defaultManager] fileExistsAtPath:pathToFile isDirectory:&isDir];

if(isFile)
{
    //it is a file, process it here how ever you like, check isDir to see if its a directory
}
else
{
    //not a file, this is an error, handle it!
}

NSFileManager*fm = [NSFileManager defaultManager];

NSURL* path = [[[fm URLsForDirectory:NSDocumentDirectory
                           inDomains:NSUserDomainMask] objectAtIndex:0]                          
                                 URLByAppendingPathComponent:@"photos"];

NSError *theError = nil;
if(![fm fileExistsAtPath:[path path]]){
    NSLog(@"dir doesn't exists");
}else
    NSLog(@"dir exists");