InvalidCastException When using ActiveX in C# project

Question

Dear all trader and API Gurus,

Thank you in advance.

Background:

Visual Studio 2010, C# Language, ActiveX OCX API as reference of project.
Successively to use the method provided by API like reqAccountUpdate and use the event to receive information about account update.

Issue:

Now I would like to require data about one specific financial instrument like a forex pair: AUD.USD .

a. Step 1: Inherit the interface of class IContract from TWSLib my Code is here as a picture and the constructor is specific for AUD.USD: a busy cat http://i.minus.com/iyG7RLuSGxiEl.jpg

As you can see that I have change the private object _combolLegs to private TWSLib.IComboLeg _comboLegs

b. Step 2: I also inherit the IComboleg and IUpdateComp to ComboLeg and UpdateComp and I do not assign any value to them since they are not related to the the AUD.USD forex trading.

c. Now I create a instance of contract and try to assign all information forex contract required for and submit my query. a busy cat http://i.minus.com/iXvgbSsp4MbYz.jpg

d. it is a runtime error. Please check the picture here: a busy cat http://i.minus.com/ifFxdfnyvfKF9.jpg

It seems like the contract instance I created could not be accepted by the api as formal IContract instance. Any idea from any .NET gurus?:)

Thanks lot in advance again,

Humble learner.

Wenhao

Edit

about the detail of IContract all I got sofar

a busy cat http://i.minus.com/iAoY8rCvbC22z.jpg

since Contract Inherits from IContract, wouldn't you just want to create an Instance of Contract you are passing IContract type to the method also it may help if you paste a copy of the IContract Interface so that we can see how it was defined. — MethodMan
– MethodMan, Commented Dec 12, 2011 at 16:07

MethodMan · Accepted Answer · 2011-12-12 16:30:57Z

1

//Try changing the way that you implement the Interface / Clase where you have 
// -- var auduse = new Contract();

//depending on boxing and unboxing from this point try to reverse it and do the following
IContract iaudUse = new Contract();
//then you would use iaudUse. what ever method in the Interface that you are wanting to use.

answered Dec 12, 2011 at 16:30

MethodMan

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4 Comments

MethodMan Over a year ago

your code / example is a bit messy you can't expect us to know what it is that your Interface / Class does if you are cutting and pasting bits and pieces also what exactly are you trying to do or accomplish.. the screen shots are nice but it's a bit messy in terms of arrangement and what you are asking us to help you with.. can you paste the full Class and the full Interface Declaration ...?

Wenhao.SHE Over a year ago

I totally do not understand which part is messy. Short words: 1. I inherit the API class 2. I use one method to submit a requestion where the method need one argument to be instance of IContract. 3. issue is casing or unboxing thing. THat is all

MethodMan Over a year ago

I am trying to follow your code but I am sure that your code is larger than the example that you pasted.. screen shots of the properties are ok but code wise don't do a lot of good since you have the code we don't only trying to help.. I apologize for my misuse in word messy.. I just can't follow what you're trying to do I need to see entry point or main method call some where

Wenhao.SHE Over a year ago

Thank you for your reply. May you give me your email address then I could share my code. It is really not long including 5 cs file and three of them are simplest inheritance class file. May i? thanks lot.!

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