计算缓存文件大小

//某个文件的大小

- (long long) fileSizeAtPath:(NSString*) filePath{

    NSFileManager* fileManager = [NSFileManager defaultManager];

    if ([fileManager fileExistsAtPath:filePath]){

        return [[fileManager attributesOfItemAtPath:filePath error:nil] fileSize];

    }

    return 0;

}

//遍历文件夹获得文件夹大小，返回多少M

- (float ) folderSizeAtPath:(NSString*) filePath{

    NSFileManager* manager = [NSFileManager defaultManager];

    if (![manager fileExistsAtPath:filePath]) return 0;

    NSEnumerator *childFilesEnumerator = [[manager subpathsAtPath:filePath] objectEnumerator];

    NSString* fileName;

    long long folderSize = 0;

    while ((fileName = [childFilesEnumerator nextObject]) != nil){

        NSString* fileAbsolutePath = [filePath stringByAppendingPathComponent:fileName];

        folderSize += [self fileSizeAtPath:fileAbsolutePath];

    }

    return folderSize/(1024.0*1024.0);

}