How to use dll generated from VB code in VC++?

Karthik Agarwal

14y7k

Hi,

I have a dll file which has been generated from VB, now i want to use it in VC++ how can i do that? Can anyone tell me how can i do that? I want to call API's by passing parameters in VB code which returns a string, how can i achieve this?

Thanks & Regards,
Karthik

44 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes14y ago
Accepted answer
In general, Windows will automatically repaint a portion of a form that has been previously hidden or obscured.

You shouldn't therefore need to refresh the form manually unless repainting is taking too long or is not working correctly for some reason.
Sam Hobbs14y ago
Yes I think you suggested a timestamp. I think the only reason I did not is because most suggestions are never implemented.
Vulpes14y ago
Yes, though as I wasn't sure initially whether it was related to the first question or not, I didn't ask Karthik to start another thread.

I agree totally that all posts should be time-stamped (not just date-stamped) and I think I may have suggested this (or seconded somebody else who suggested it) in a previous thread.
Sam Hobbs14y ago
So are you saying that after discussing the initial question, the discussion continued with a totally different question?

Also, I will say again; I think it is best to get clarification first. That could save time for everyone.

Excuse me for the following, which is less relevant to this thread. I think it would help to have the time of every post shown for the post. In other words, it would help if the forum software were to show the time as well as the date of each post. Then I would have a better idea of when things happen. I often do not have a lot of time to look at the forums but if I know when is a good time to look then I would be able to schedule my time better. Also, I intended to look at this thread closer but I am not sure how to refer to previous posts if I were to comment on the previous discussions. A timestamp would help with that too. So now I have adequate justification for requesting that threads have the time for each post shown as was done in the past.
Karthik Agarwal14y ago
No Vulpes I am done with it, there was something wrong with my code hence i sorted it out on accepted the answer as well.

And if it comes to what Sam is saying, i am not sure in what way he looks into my posts. Me and Vulpes are in sync we both understood what we are doing and what we have ended up with.

I said him many a number of times i am ready to take up your suggestions provided it comes at the earliest. Sam referring to your previous comment about my reply to some post not sure what was that post. When i have time and felt like looking into the posts, if i feel like i can do something regarding that post i did as much as i can. Which isn't wrong i hope!
Vulpes14y ago
Karthik,

I can't think of any reason why reloading an XML file should affect matters unless the menu is being partly populated with values from that file.

Sam,

When questions in these forums are not completely clear (and, let's face it, not many are), I often look at previous threads to fill in the gaps.

My opening post, which was 4 lines long, started with the line:

"Regarding calling a VB.NET dll from C++/CLI, check out this earlier thread where I provided a simple example:"

If the assumptions in that line were incorrect, then Karthik would no doubt have corrected me but did not.

We've already established that (after some initial problems with namespaces) the VB.NET dll can be called from his C++/CLI Windows Forms application.

We're now trying to solve a problem with hiding or disabling Karthik's menu whilst it is being populated with values from the Excel sheet. If you have any suggestions in that regard, then I'm sure Karthik would welcome them.
Sam Hobbs14y ago
Vulpes, I really think it is more efficient for everyone to first clarify the problem; it was not clear in the beginning. For example, I would have first asked if this is VB .Net; I would not have assumed it. I also would have clarified if this is an unmanged or managed C++ program.

It seems highly unlikely that a VB .Net class library cannot be called by a managed C++ program. I cannot help though because the two of you again are wandering around in the dark. I think it would be beneficial for both you to learn how to clarify what the problem is; be more methodical about it.

Karthik, in response to your response to Hermant, do you try to answer questions around here? If not then you do not have experience with the problem of people asking questions without adequately searching. It happens multiple times everyday.
Karthik Agarwal14y ago
I tried using visible property Vulpes it works fine for the very first time but i couldn't understand why it's not working when i close and open again. Actually I will read an xml file into the windows form after loading the form, so when i load the form and read the xml file for the very first time it works pretty fine. When i close the xml file then load the same xml file again it isn't working fine. While closing and opening the xml windows form is not closed. It means when the form is closed and opened only the feature is working fine. Have you got idea why is it like this?
Karthik Agarwal14y ago
In fact that's a very complex form, may be i will retry using refresh as well after that i'll get back to u. if that works fine probably i am done.
Karthik Agarwal14y ago
I tried that as well which didn't work as expected. I think when the menu item is invisisble we will not be able to add the dropdown items to that. Only doubt i got was do i need to refresh the windows form if i have to see the change in enabling and disabling or invisible visible property.
Vulpes14y ago
Instead of disabling the menu why don't you hide it (set Visible property to false) until you're in a position where the user can safely click it?
Karthik Agarwal14y ago
Vulpes i just need your final thought on the last problem i have.
After reading that excel sheet through dll i need to populate menu items in VC++ windows form. If i read the excel sheet in background how is it possible to populate menu while loading windows form where that menu should also get loaded as well. I just need one column of excel sheet to be populated in menu. So i wrote an inspect function in VB which returns the whole list which i need to populate in menu. Even though i populate menu those menu items may cause exception if someone clicks that before i read the other part of the excel sheet. So i tried disabling the menu till i read then i tried enabling the windows which isn't working fine. I also tried disabling the menu and then finally after reading the whole excel file i tried adding menu items which can't be done when menu is in disabled state. What shall i do solve this problem. Do lead so that i will close stuff ASAP. For any further queries please post in return.
Karthik Agarwal14y ago
Yup got it i didn't call RunWorkerAsync() method should see how it works and how much time it takes to read and populate.
Vulpes14y ago
You need to call the RunWorkerAsync() method to start the background task.

The DoWork event will then be fired automatically and the appropriate arguments passed to the eventhandler (you don't need to do anything in that regard).

If you've done this and it's still not firing, then the chances are that the event has not been wired up to the handler.

If you've added the BackgroundWorker component via the VS designer, then you should have a line like this in your InitializeComponent() method:

backgroundWorker1->DoWork += gcnew DoWorkEventHandler(this, &Form1::backgroundWorker1_DoWork );

Otherwise, you'll need to add it manually - perhaps in Form1_Load.
Karthik Agarwal14y ago
I have created an backgroungworker and moved the function call of reading excel sheet into the event handler of DoWork . But DoWorkEvent of that isn't getting called. Will that event be called automatically or else do i need to call that manually from a specific place or what? If i need to call what are the parameters i should be passing to that? These questions are not answered in the link you provided.
Vulpes14y ago
I'd use a BackgroundWorker:

http://msdn.microsoft.com/en-us/library/system.componentmodel.backgroundworker.aspx

This will enable you to read the Excel sheet on a background thread as well as provide an easy way to communicate progress/completion to the UI thread.
Karthik Agarwal14y ago
What i did is i created an instance in only one place and kept them in a global variable so that i can use in all the places from my application as you said and it is working fine.

Now my problem is when i associate my dll with this application and try to read the excel sheet while loading windows form is taking around 15 secs which is not acceptable. So i am planning to read the excel sheet in the background after loading windows form. I will load the windows form first and then i will start reading the excel file. Is there any function where in i can call a function in the background or background process kind of stuff.
Vulpes14y ago
Here's a simple example of using global variables in C++/CLI.

Notice that we house these in a class called G and make them static.

They're then populated in class B but we can still access them from class A:

#include "stdafx.h"

using namespace System;
using namespace System::Collections::Generic;

ref class G // class to hold global variables
{
internal:
static List^ List;
static Dictionary^ Dict;
};

ref class A
{
public:

void MethodA()
{
if(G::List != nullptr)
{
for each (String^ s in G::List) Console::WriteLine(s);
}

if(G::Dict != nullptr)
{
for each(String^ key in G::Dict->Keys) Console::WriteLine("{0} : {1}", key, G::Dict[key]);
}
}
};

ref class B
{
public:

void MethodB()
{
// assign to global variables
G::List = gcnew List();
G::List->Add("Karthik");
G::List->Add("Vulpes");
G::Dict = gcnew Dictionary();
G::Dict->Add("First", "One");
G::Dict->Add("Second", "Two");
}
};

int main(array ^args)
{
B^ b = gcnew B();
b->MethodB();
A^ a = gcnew A();
a->MethodA();
Console::ReadKey();
return 0;
}
Karthik Agarwal14y ago
Never mind can you state an example which would do better. I am breaking my head to do this. If this is done i can leave home a bit relaxed.
Vulpes14y ago
I'd create global variables and assign the List and Dictionary instances to these. You'll then be able to access them throughout the application.
Karthik Agarwal14y ago
I have created an instance of the namespace of the dll and accessing the List and dictionary present in the dll, but i want to use the List and dictionary in multiple places (I mean multiple .h and .cpp files). If i create instance in multiple places it is clearing off the contents of the List and dictionary and hence can't use them in multiple places. Please tell me how can i use that in multiple places?

Note: If i can't use in multiple places the dll will be of no use right. Probably there should be a way to do that but i am not aware of it

I am working on Visual studio 2008 (.Net Framework 3.5)
Vulpes14y ago
Well, there's no escaping from the fact that Excel interop is very slow as each call to the Excel object model involves considerable overhead.

What's usually suggested for improving performance is to first load the contents of the spreadsheet (or the part you're interested in) into a two dimensional array which can be done much more quickly than obtaining the contents of each cell individually.

You can then do your manipulations on the elements of the array.

There's a Microsoft support article here with some sample code:

http://support.microsoft.com/kb/302094/en-us
Karthik Agarwal14y ago
Excel sheet
Karthik Agarwal14y ago
dll project
Karthik Agarwal14y ago
I have one more problem, the problem now is that there is huge amount of delay which has been involved in reading the excel sheet in VB. I feel there's nothing wrong with the way i am reading but i am not sure whether that's an optimized way or not. It is taking around 30 seconds to read which is unacceptable. Please find the attachment for the code which i wrote along with the excel sheet, please suggest an optimized way or correct me if i am wrong.

1. Language_Feature the dll (place where i am reading excel sheet and generating dll)
2. Language_Test is the test application
3. Language is the excel sheet
Karthik Agarwal14y ago
I have seen this before when i tried to google about how to do this but i thought it was about reading charts and left it like that. As you said i will read it and try to implement and will post in return if i get any doubts.
Vulpes14y ago
You're in luck :)

I've found a good article about automating Excel using C++/CLI:

http://www.codeproject.com/KB/office/automate_excel.aspx

I'd read it through then have a go at translating your VB.NET code directly to C++/CLI.

I'll try and help if you get struck.
Karthik Agarwal14y ago
everything is working pretty fine now. But i have no idea how to do that in VC++? So need some support to implement in VC++ bcoz that would make things simple for if the way to do is not complex. I need to know the easiest procedure to read excel sheet in VC++? I neither know ODBC or data table to implement that in VC++!
Vulpes14y ago
I mean that there's no reason in principle why you can't do it in C++/CLI in exactly the same way as you're doing it now in VB.NET, whether that be via Office Interop and the Office PIAs or by creating an ODBC connection and reading the Excel spreadsheet into a DataTable.

However, unless it's just a few lines of code, I see no point in translating it. I'd stick to using the VB.NET dll if that's working OK now.
Karthik Agarwal14y ago
Anyways next time i am not gonna give same name as i already faced a problem.

If you say it that way how can i proceed implementing it? That i doesn't have much time for doing that? Should that be read as database or ODBC something of that kind, anyways i will look into that option if it's same way as VB is, otherwise i am not even gonna try that which will make things complex for me.

Anyways what's your suggestion?
Vulpes14y ago
Let's face it, it's not a good idea to give programming entities the same name so I don't think it's unreasonable to give the class a different name to the namespace in the VB.NET project.

I think you probably could rewrite the VB.NET Office Interop code in C++/CLI though your hair might be somewhat diminished by the end of it :)
Karthik Agarwal14y ago
May be but the problem exits in VB.

Do you mean to say that rewriting or converting the same VB code in VC++ will do the job?
Vulpes14y ago
Hmm, it looks like ambiguity problems arise if a namespace contains a class of the same name, though I can get it to work in C# by always qualifying the class name with the namespace:

using System;
using Language;

namespace Language
{
public class Language
{
public void MyMethod()
{
Console.WriteLine("Hello");
}
}
}

class Program
{
static void Main()
{
Language.Language lang = new Language.Language(); // compiles OK
lang.MyMethod();
Console.ReadKey();
}
}

I don't think I've ever tried to access the Office PIAs from C++/CLI.

In fact, even though I predominantly use C#, I always used to use VB.NET for Office Interop because (until version 4.0 came along) it was a pain to do it from C#.

The Office PIAs were largely written for the VBA programmer which is why they're such a good fit for VB.NET.

However, it shouldn't be too bad to access them from C++/CLI because you do have support for optional and indexed properties which was lacking until recently from C#.

Nevertheless, now you've got it going using the VB.NET dll, I wouldn't bother rewriting it - there's little point in rewriting anything in .NET which (as long as you stick to the CLS) is language-agnostic.
Karthik Agarwal14y ago
Vulpes actually i was doing everything right but the problem was i gave the project name and class name Language_Feature which is same hence it was not accepting it that now i changed the class name as Language_Features and immediately it is working fine. This is that visual studio doesn't accept the project name and class name to be same. It seems like even you haven't noticed it. I knew that i kept the same name but i have not expected this kind of thing in visual studio. What difference it makes for it if both the names are same?

Also tell me how tough is it to read excel sheet in VC++?

Anyways after a bit of hard work and your support i have learned a very good lesson for the day.
Vulpes14y ago
Don't add the extra namespace to the VB class library project:

Public Class Language_Feature

Public Function Read(ByVal path)

//does something

End Function

End Class

You should then be able to access the above class from the C++/CLI project as follows:

#include "stdafx.h"

using namespace System;
using namespace Language_Feature; // root namespace of VB.NET dll

public:
static Language_Feature ^ obj; // should not now need any further qualification

//constructor
{
obj = gcnew Language_Feature();
}
Karthik Agarwal14y ago
The only reason why i have to move to VB is to read an excel sheet otherwise i would have continued with VC++. People say and even i feel it's easier to read or write to excel sheet. I am not sure how that can be done in VC++ hence i created a dll using VB and using the same in VC++ with which i succeeded.

Vulpes is it that tough to read excel sheet in VC++. I find the same references mirosoft.excel and office in VC++ as well then can i use them in the i do in VB itself ot it's bit different or difficult what's your take on this?

I would love to do it VC++ if it's not too tough which solves many of my problems and the complexity as well.
Karthik Agarwal14y ago
I just want to access the functions in that dll. I am able to do that in the way i said in the previous post but it isn't fine the way i am accessing the functions using two namespace's. If i wont write one more namespace as i said previously or change the root namespace to Language i am not able to access the functions in the dll. So how can i do that using single namespace either the Language namespace or project name which is Language_Feature namespace which will avoid confusion.
Vulpes14y ago
If you've called the VB.NET project, Language_Feature, then there's probably a 'root' namespace of that name. If you've then created another namespace called "Language", then that will be a 'nested' namespace of the root and it would explain the behaviour you're seeing.

You can check this by examining the VB.NET project's properties under the Application tab.

One reason why I dislike developing in VB.NET is because too much is hidden away for my liking :(
Karthik Agarwal14y ago
As you said in the older post i did as follows:

// classlibrary1.vb

Namespace Language

Public Class Language_Feature

Public Function Read(ByVal path)

//does something

End Function

End Class

End Namespace

#include "stdafx.h"

using namespace System;
using namespace Language_Feature;// Even thought the namespace is Language It says it doesn't have any namespace of that kind but where as when i type Language_Feature then the IDE says it's fine how is this happening i don't understand.
public:
static Language_Feature::Language::Language_Feature ^ obj;//this is working fine but it isn't the way it should be
//constructor
{
obj = gcnew Language_Feature::Language::Language_Feature();//this is working fine but it isn't the way it should be
}
Vulpes14y ago
Regarding add a reference to the VB.NET dll, I don't think I can explain it any more clearly than I did the last time. What specific problem are you having?

Incidentally, the VB.NET dll must be precompiled - you can't just add the source code as a separate project because Visual Studio doesn't support multi-language solutions.

The code to 'new up' the VB.NET class, call the appropriate method and pass it a string can be placed anywhere in the application - it doesn't have to be in the main() method.
Karthik Agarwal14y ago
Vulpes i am working on windows form application in vc++, where i will browse for the excel file path from vc++ application and pass the same to the VB dll which will read the whole excel sheet for which i already have a specific API written in VB dll. In this case there won't be any main() in windows form application right how to proceed and also i want little more clarity on the way how to add reference to the VB dll from vc++
Vulpes14y ago
Regarding calling a VB.NET dll from C++/CLI, check out this earlier thread where I provided a simple example:

http://www.c-sharpcorner.com/Forums/Thread/140137/way-to-use-an-exe-which-is-generated-using-vb-in-vc.aspx

Sorry, I didn't really follow the second part of the question. If you mean that you want to pass parameters to a VB.NET method which then returns a string, you can do that in just the same way as if the method had been written in C++/CLI.
Karthik Agarwal14y ago
Hi Lakshmi,

If google would have solved my problem i would not have asked it here. Anyways thanks for googling. I need in detail explanation so only i came up here. I have already seen these which couldn't solve my problem.

Thanks & Regards,
Karthik
Hemant Kumar14y ago
Refer this links
http://www.developerfusion.com/article/1973/calling-a-c-dll-from-visual-basic/

http://www.codeproject.com/KB/COM/vb_from_vc.aspx