iphone – how to check if the file is a directory , audio , video or image?

Sample Code :

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSArray *directory = [[NSFileManager defaultManager] directoryContentsAtPath: documentsDirectory];
BOOL isDirectory;
for (NSString *item in directory){
    BOOL fileExistsAtPath = [[NSFileManager defaultManager] fileExistsAtPath:item isDirectory:&isDirectory];
    if (fileExistsAtPath) {
       if (isDirectory)
       {
           //It's a Directory.
       }
    }
    if ([[item pathExtension] isEqualToString:@"png"]) {
       //This is Image File with .png Extension
    }
}

You can also use Uniform Type Identifiers as explained by Bavarious here.

Sample Code :

NSString *file = @"…"; // path to some file
CFStringRef fileExtension = (CFStringRef) [file pathExtension];
CFStringRef fileUTI = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, fileExtension, NULL);

if (UTTypeConformsTo(fileUTI, kUTTypeImage)) NSLog(@"It's an image");
else if (UTTypeConformsTo(fileUTI, kUTTypeMovie)) NSLog(@"It's a movie");
else if (UTTypeConformsTo(fileUTI, kUTTypeText)) NSLog(@"It's text");

CFRelease(fileUTI);