How to access a class in a namespace which is in different project?

Karthik Agarwal

15y3.1k

Hi,

I have three projects under another project of which each contains one namespace. Now among them i need to call a class which is under a namespace in visual studio 2008. Please don't ask me to add the dependencies to the main project so that i can access the namespace and all the classes in that just like local namespace which i can't do due to some restrictions. Tell me something like derived class concept so that i can access that class.

The LanguageTable class which i want to call is as follows:

#pragma once

#include "resource.h"

#using
#using
#using
#using
#using

using namespace System;
using namespace System::Xml;
using namespace System::ComponentModel;
using namespace System::Drawing;
using namespace System::Windows::Forms;
using namespace System::IO;
using namespace System::Collections::Generic;
using namespace System::Runtime::InteropServices;

#define GFX_LANGUAGE_MAX 20

namespace gfx_viewer_win32
{

public ref class LanguageTable
{
public:
    static Dictionary^> ^ language_string_table;
    static array ^language_string_id;
    static StreamReader^ LanguageReader;
    static String ^ copy_of_language_path;
    static String ^ copy_of_clicked_language;
    static String ^ max_dec_string;
    static String ^ max_hex_string;
    static bool load_OK_btn = false;

     LanguageTable(void)
    {
        language_string_id = gcnew array(0);
    }
     ~LanguageTable(void)
    {
        if(LanguageReader)
        {
           delete LanguageReader;
        }
        delete language_string_id;
        delete language_string_table;
    }
};
}

The place from where i want to call LanguageTable class is as follows:

// Code_generator.h

#pragma once

#using
using namespace System;
using namespace System::Drawing;
using namespace System::Drawing::Imaging;
using namespace System::Text;
using namespace System::Xml;
using namespace System::Collections;
using namespace System::Collections::Generic;
using namespace System::IO;
using namespace System::Globalization;
using namespace System::Windows;
using namespace System::Windows::Media;
using namespace System::Windows::Media::Imaging;
using namespace gfx_coder_prj_parser;

namespace Code_generator
{
public ref class CCodeGenerator : CCodeParserMultiLayer
    {
     public:
       String ^ codegen_path;
       int l_compressed_images_present;
       CCodeGenerator(void)
       {
       }
       ~CCodeGenerator(void)
       {
       }
//============I want to call LanguageTable class from here==========
    };
}

15 Replies

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

Vulpes15y ago
Accepted answer
If they've been combined into a single project, then there should be no problem accessing the class from elsewhere in the project:

// Code_generator.h

#pragma once

#include "gfx_viewer_win32.h" // if it's in a separate file

#using

using namespace System;
using namespace System::Drawing;
using namespace System::Drawing::Imaging;
using namespace System::Text;
using namespace System::Xml;
using namespace System::Collections;
using namespace System::Collections::Generic;
using namespace System::IO;
using namespace System::Globalization;
using namespace System::Windows;
using namespace System::Windows::Media;
using namespace System::Windows::Media::Imaging;
using namespace gfx_coder_prj_parser;
using namespace gfx_viewer_win32; // import namespace to current file

namespace Code_generator
{
public ref class CCodeGenerator : CCodeParserMultiLayer
{
public:
String ^ codegen_path;
int l_compressed_images_present;
CCodeGenerator(void)
{
}
~CCodeGenerator(void)
{
}

void SomeMethod(void)
{
LanguageTable ^ languageTable = gcnew LanguageTable();
// do something with languageTable
}
};
}
Vulpes15y ago
Good thinking, Karthik :)
Karthik Agarwal15y ago
finally got an idea to do. Now what i will do is that i will copy LanguageTable class in gfx_coder_kepler which is already dependent on gfx_viewer_win32 and then i will inherit the same in the place gfx_viewer_win32 where i was using it previously. That solves my problem.
Vulpes15y ago
As a general rule, classes which have dependencies on each other need to be in the same project. You can then use forward declarations to deal with the problem of classes being used before they've been defined.

One thing you could do is to move all mutually dependent classes out into a fourth project and you could then add a reference to this fourth project to the other projects which need it. This, of course, would no longer be circular.

However, if you only have two such classes, then a better idea IMO would be to move one of them out of its present project and into the other. Mutual project references will then no longer be needed.
Karthik Agarwal15y ago
Ya the fact is that i have three project's under one solution. Anyway is there any other solution which you could give rather removing the reference from LanguageTable to Codegenerator.h which i already have and will not be able to modify as i have some things inherited from codegenerator.h to LanguageTable
Vulpes15y ago
So, you do in fact still have three projects under one solution :)

The project which contains Code_generator.h needs a reference to the project which contains the LanguageTable class. However, the latter doesn't need a reference to the former - if you've added one, you need to remove it first to avoid the circular dependency.
Karthik Agarwal15y ago
Finally you got me. I added mutual references to each project. If this is the case how should i use the LanguageTable class without causing circular dependency problem.
Vulpes15y ago
If you've combined three projects into a single project under the one solution, then you no longer need to add any project references as there's just one project now.

The circular dependency probably arose when you had three separate projects because you'd added mutual references to two or all three of the projects.

You'll just need to include the file which contains the LanguageTable class in Code_generator.h so that the class is defined before it's used.

All the 'using namespace' directive does is to avoid the need to fully qualify the LanguageTable class with its namespace every time you use it.
Karthik Agarwal15y ago
Sorry to trouble you too much Vulpes, but that's not an error message which we get it in the error window. When i try to add project dependencies through project menu and then properties -> then add new reference to in the dialog box that appears -> then projects tab again -> list down all the projects in the current solution. If i select gfx_viewer_win32 its showing a message box which says "Could not add a project reference to the project with identifier {5CCE9750-0DB9-4514-83E4-C85040CA57E8} because it would cause a circular dependency"

what i want to know exactly is: even though i have added three projects under a single project but each namespace should be able to find other namespace right, what should i do for that.?

What exactly i should do when i want to make the one project known to another project?
Vulpes15y ago
Well, it wasn't apparent to me from the code you posted that there would be a circular dependency though a way can usually be found to resolve these.

Can you post the actual error message, so we can try to figure out what needs to be done.
Karthik Agarwal15y ago
Just you couldn't get me i guess. If i am not wrong i can never right the following line

using namespace gfx_viewer_win32;

in the code untill and unless and unless i have project dependencies right? I already told you that i can't add it in project dependencies as it is allowing me to do that due to circular dependencies problem. Hence i can't use your solution i think.
Karthik Agarwal15y ago
Hi Vulpes,

Probably after reading your reply again i got to know that you misinterpreted my question. I said that three of my projects are combined i.e added under single main project. Even though those three are different projects now they got combined under single main project na. Then how come i will not be able to access it in anyway. You must rethink on this i guess.
Vulpes15y ago
I don't see how you can derive from a managed class in a different project unless you have the metadata and IL for that class and the only way to get that is to add a reference to its project file.

However, if you have a link which says differently, I'd be happy to look at it.
Karthik Agarwal15y ago
But i heard it like it can be done through deriving that class which i want to call by using main() function. Are you sure about that i can do that?
Vulpes15y ago
Well, I'm sorry but you can't access, or inherit from, a class in a different project unless you add a reference to that project to your current project.

If, for some reason, you can't do that then I'd just copy and paste the source code for the LanguageTable class into your current project and include any additional files it needs in that.