Object reference not set to an instance of an object

Question

I'm getting a NullReferenceException in this block of code when I try to set the value for responseStatusCode (4th line down). I've declared strings this way many times before and I'm confused as to why it's throwing an error here. Any suggestions? Thanks!

Here's the block of code that's throwing the exception.

private bool voidLabelAndProcessResults(string shipper, string sc, string msn)

{

XmlDocument doc = ConnectShipUPS.VoidRequest(shipper, sc, msn);

string responseStatusCode = doc.SelectSingleNode("VOIDRESPONSE/RESPONSESTATUSCODE").Value;

return responseStatusCode == "0";

}

Brandon Lewis · Answer

What does the _processXMLRequest(XmlDocument doc) return? Since your returning whatever that method is returning we may have to dig a little deeper into the methodarchy. It looks like your XPathNavigator is assigning to the document correctly. However something may be going wrong when the _processXMLRequest() method is being called.

Jayson · Answer

I think you are right Brandon. Here's the code for the VoidRequest method if that helps at all. Thanks. #region VoidRequest /// /// Sends a Void request to be processed by ConnectShip /// /// shipper (code for the warehouse the item was shipped from) /// sc (label type) /// msn (code returned from UPS about the label) /// XmlDocument results public static XmlDocument VoidRequest( string shipper string sc string msn) { try { XmlDocument doc = new XmlDocument (); doc.LoadXml( RawXML .VoidRequest); XPathNavigator xn = doc.CreateNavigator(); xn.SelectSingleNode( /VOIDREQUEST/LOGIN/LOGINID ).SetValue( TEST ); xn.SelectSingleNode( /VOIDREQUEST/LOGIN/PASSWORD ).SetValue( TEST ); xn.SelectSingleNode( /VOIDREQUEST/SHIPPER ).SetValue(shipper); xn.SelectSingleNode( /VOIDREQUEST/SC ).SetValue(sc) ; xn.SelectSingleNode( /VOIDREQUEST/MSNLIST/MSN ).SetValue(msn); return _processXMLRequest(doc); } catch ( Exception ex) { throw (ex); } } #endregion

Brandon Lewis · Answer

Actually you need not create a new instance of an XmlDocument class so long as the method you are using to assign to the XmlDocument instance is returning a value the type of XmlDocument. This line: XmlDocument doc = ConnectShipUPS .VoidRequest(shipper sc msn); Will work fine so long as the VoidRequest(shipper sc msn); method is returning an instance of an XmlDocument. The instance of XmlDocument doc will simply be the result of calling the VoidRequest method. However if the VoidRequest method isnt returning the proper value then that will be where the problem lays = ) Check to see if the file is being properly assigned to the XmlDocument instance before it is being returned from the method. An invalid file path to the xml document will cause a null reference exception. What makes me think that the VoidRequest method is returning a null is because he isnt getting an InvalidCastException which would indicate that whatever is being returned from that method cannot be cast to type XmlDocument. Of course I could be wrong... but thinking logically the way he was trying to do it should work so long as the VoidRequest method is working correctly. Example: public static class ConnectShipUps { //Doing it without parameters for simplicity //Return type of XmlDocument public static XmlDocument VoidRequest() { XmlDocument myDoc = new XmlDocument (); //Make sure the file path is valid. myDoc.Load(filepath.xml); //Return the XmlDocument object. return myDoc; } } private bool voidLabelAndProcessResults( string shipper string sc string msn) { XmlDocument doc = ConnectShipUps .VoidRequest(); }

Ryan Alford · Answer

You must create an instance of the XmlDocument before you use it. Try this: private bool voidLabelAndProcessResults( string shipper string sc string msn) { XmlDocument doc = new XmlDocument (); doc = ConnectShipUPS .VoidRequest(shipper sc msn); string responseStatusCode = doc.SelectSingleNode( VOIDRESPONSE/RESPONSESTATUSCODE ).Value; return responseStatusCode == 0 ; }

Brandon Lewis · Answer

Is the XmlDocument doc being set to a value? It looks like it is but this line: XmlDocument doc = ConnectShipUPS .VoidRequest(shipper sc msn); may not be returning anything to give doc a value so when you try to access one of its members it throws a NullReferenceException. I would make sure that doc is being given a value and if not move into the ConnectShipUPS class and see whats going on and why no value or a null value is being returned.