c# webbrowser获取cookies

//取出Cookie，当登录后才能取
[DllImport("wininet.dll", CharSet = CharSet.Auto, SetLastError = true)]
static extern bool InternetGetCookieEx(string pchURL, string pchCookieName, StringBuilder pchCookieData, ref System.UInt32 pcchCookieData, int dwFlags, IntPtr lpReserved);
private static string GetCookies(string url)
{
uint datasize = 1024;
StringBuilder cookieData = new StringBuilder((int)datasize);
if (!InternetGetCookieEx(url, null, cookieData, ref datasize, 0x2000, IntPtr.Zero))
{
if (datasize < 0)
return null;

cookieData = new StringBuilder((int)datasize);
if (!InternetGetCookieEx(url, null, cookieData, ref datasize, 0x00002000, IntPtr.Zero))
return null;
}
return cookieData.ToString();
}