中文GBK 編碼 转换为 UTF-8编码，或者判断有中文text的字节长度

NSStringEncoding enc = CFStringConvertEncodingToNSStringEncoding(kCFStringEncodingGB_18030_2000);
        
        NSString* nameStr = [detailTextView.text stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
        
        
        NSData* nameData = [nameStr dataUsingEncoding:enc];
        NSUInteger nameLength = [nameData length];

NSString *newString = [[NSString alloc] initWithData:dataString encoding:enc];    有中文string 转为国际编码string，或者说 NSString 符合GBk编码