Using XE Currency Restful API in AX - Using Basic Authentication method

static void XECurrencyConverionRestfulAPI(Args _args)
{
    System.Net.HttpWebRequest           webReq;
    System.Net.HttpWebResponse          webRes;
    CLRObject                           clrObj;
    System.IO.Stream                    stream;
    System.IO.StreamReader              streamRead;
    System.IO.StreamWriter              streamWrite;
    System.Net.ServicePoint             servicePt;
    System.Net.WebHeaderCollection      headers = new System.Net.WebHeaderCollection();
    str                                 userNamePassword, userNamePassword64, ret;
    System.Byte[]                       byte;
    System.Text.Encoding                encoding = System.Text.Encoding::get_UTF8();
 
    //This line gives the user control to run unmanaged and managed code
    new InteropPermission(InteropKind::ClrInterop).assert();
    // Create Object for adding headers
    headers = new System.Net.WebHeaderCollection();
    clrObj = System.Net.WebRequest::Create('https://xecdapi.xe.com/v1/currencies.xml');
    webReq = clrObj;
    //Set Method Type
    webReq.set_Method("GET");
    webReq.set_KeepAlive(true);
    // Set Content type
    webReq.set_ContentType("application/xml");
 
    try
    {
        userNamePassword = 'YOURUSERNAME:YOURPASSWORD';
        //64 bit encode user name and password
        byte = encoding.GetBytes(userNamePassword);
        userNamePassword64 = System.Convert::ToBase64String(byte);
        headers.Add("Authorization", 'Basic ' + userNamePassword64);
 
        //Add header to request
        webReq.set_Headers(headers);
        //Gets the response object
        webRes = webReq.GetResponse();
    }
    catch (Exception::CLRError)
    {
        //Access the last CLR Exception
        info(CLRInterop::getLastException().ToString());
     
        //See AifUtil::getClrErrorMessage for another alternative
        //how to parse the Exception object
    }
    //Get Stream
    stream = webRes.GetResponseStream();
    streamRead = new System.IO.StreamReader(stream);
    ret = streamRead.ReadToEnd();
    stream.Close();
    webRes.Close();
}

Unable to cast object of type 'Dynamics.Ax.Application.DictField' to type 'Dynamics.Ax.Application.SysDictField

I found some standard Microsoft code in AX which was working fine in x++ however, when the code executed in IL (Aif Interface), it would throw an error

"Unable to cast object of type 'Dynamics.Ax.Application.DictField' to type 'Dynamics.Ax.Application.SysDictField"

I found that the variable was declared as SysDictField but the object was instantiated as new DictField() - this works fine in x++ but would fail in IL based on OOP principles. 

The solution was to change the following line of code from new dictField(...) to new sysDictField(...)

SysDictField        dictField;

dictField   = new dictField(_variable.RefTableId,_variable.RefFieldId);

should be:

dictField   = new SysDictField(_variable.RefTableId,_variable.RefFieldId);