SetKeyChainStorage.cs

private void SetKeyChainStorage(string theUserID)
{
	var rec = new SecRecord (SecKind.GenericPassword){
		Generic = NSData.FromString ("active_user_id") //this is the KEY
	};

	SecStatusCode res;
	var match = SecKeyChain.QueryAsRecord (rec, out res);
	if (res == SecStatusCode.Success) {
		//found the key, so just update the value
		var updateTheID = new SecRecord (SecKind.InternetPassword) {
			ValueData = theUserID,
			Generic = NSData.FromString ("active_user_id")
		};

		var err = SecKeyChain.Update(match, updateTheID);

		if (err != SecStatusCode.Success) {
			Console.WriteLine (err.ToString());
		}
	}
	else
		//didnt find the key so create it, and set the value
	{
		var setTheID = new SecRecord (SecKind.GenericPassword) {
			ValueData = theUserID,
			Generic = NSData.FromString ("active_user_id")
		};

		var err = SecKeyChain.Add (setTheID);

		if (err != SecStatusCode.Success) {
			Console.WriteLine ("problem setting theuserID");
		}
	}
}