无法从Xamarin iOS SecKeychain检索GUID

using System;
using System.Runtime.InteropServices;
using MonoTouch.Security;

public static string RetrieveGUIDFromKeychain()
{
    IntPtr query = IntPtr.Zero;
    IntPtr result = IntPtr.Zero;
    string guid = null;

    try
    {
        // 创建查询字典
        query = SecKeychainUtil.CreateQueryDictionary("MyGUID", SecKind.GenericPassword);

        // 在密钥链中搜索匹配的项
        SecStatusCode status = SecKeychain.Search(query, out result);

        if (status == SecStatusCode.Success && result != IntPtr.Zero)
        {
            // 从结果中提取GUID
            SecKeychainItem item = new SecKeychainItem(result);
            guid = item.GetAttribute(SecAttributeKey.Account);
        }
    }
    finally
    {
        // 释放资源
        if (query != IntPtr.Zero)
            Marshal.FreeHGlobal(query);

        if (result != IntPtr.Zero)
            CFRelease(result);
    }

    return guid;
}

string guid = RetrieveGUIDFromKeychain();
Console.WriteLine("Retrieved GUID: " + guid);