NSFileManager相关

枚举相同格式的文件：
You can achieve this pretty easily with the help of NSPredicate, like so:

NSString *bundleRoot = [[NSBundle mainBundle] bundlePath];
NSFileManager *fm = [NSFileManager defaultManager];
NSArray *dirContents = [fm contentsOfDirectoryAtPath:bundleRoot error:nil];
NSPredicate *fltr = [NSPredicate predicateWithFormat:@"self ENDSWITH '.jpg'"];
NSArray *onlyJPGs = [dirContents filteredArrayUsingPredicate:fltr];

Checking for file existence:

+(BOOL)fileExistsAtAbsolutePath:(NSString*)filename {
    BOOL isDirectory;
    BOOL fileExistsAtPath = [[NSFileManager defaultManager] fileExistsAtPath:filename isDirectory:&isDirectory];

    return fileExistsAtPath && !isDirectory;
}

Checking for directory existence:

+(BOOL)directoryExistsAtAbsolutePath:(NSString*)filename {
    BOOL isDirectory;
    BOOL fileExistsAtPath = [[NSFileManager defaultManager] fileExistsAtPath:filename isDirectory:&isDirectory];

    return fileExistsAtPath && isDirectory;
}