iOS计算文件或者文件夹大小

需要计算文件夹大小，网上看到过一些代码，但是不完全正确，因为没考虑文件夹下面包含文件夹的情况，所以需要递归计算下。

//单个文件的大小
- (long long) fileSizeAtPath:(NSString*) filePath{
    NSFileManager* manager = [NSFileManager defaultManager];
    if ([manager fileExistsAtPath:filePath]){
        return [[manager attributesOfItemAtPath:filePath error:nil] fileSize];
    }
    return 0;
}
//遍历文件夹获得文件夹大小，返回字节
- (long long ) folderSizeAtPath:(NSString*) folderPath{
    NSFileManager* manager = [NSFileManager defaultManager];
    if (![manager fileExistsAtPath:folderPath])
        return 0;
    NSString* fileName = [folderPath copy];
    long long folderSize = 0;
   
    BOOL isdir;
    [manager fileExistsAtPath:fileName isDirectory:&isdir];
    if (isdir != YES) {
        return [self fileSizeAtPath:fileName];
    }
    else
    {
        NSArray * items = [manager contentsOfDirectoryAtPath:fileName error:nil];
        for (int i =0; i<items.count; i++) {
            BOOL subisdir;
            NSString* fileAbsolutePath = [fileName stringByAppendingPathComponent:items[i]];

            [manager fileExistsAtPath:fileAbsolutePath isDirectory:&subisdir];
            if (subisdir==YES) {
                folderSize += [self folderSizeAtPath:fileAbsolutePath]; //文件夹就递归计算
            }
            else
            {
                folderSize += [self fileSizeAtPath:fileAbsolutePath];//文件直接计算
            }
        }
    }
    return folderSize; //folderSize/(1024*1024)递归时候会运算两次出错，所以返回字节。在外面再计算
}