Use instance fields and properties from .NET DLL in C++ app

This article provides an introduction to cross-technology handling of static fields and properties.
Javonet allows you to reference and use modules or packages written in (Java/Kotlin/Groovy/Clojure, C#/VB.NET, Ruby, Perl, Python, JavaScript/TypeScript) like they were created in your technology. If have not yet created your first project check Javonet overview and quick start guides for your technology.

With Javonet you can interact with instance field and properties from .NET DLL like they were available in C++ but invocation must be performed through Javonet SDK API.

Javonet allows you to pass any C++ value type as argument to method from .NET DLL. For reference type arguments (instances of other classes) you can create such instance with Javonet and pass the Invocation Context variable referencing that object as argument of method invocation.

Custom .NET DLL with instance fields and properties

With Javonet it is possible to reference any custom .NET DLL and interact with public instance fields and properties declared on types defined within that module almost the same as with any other C++ library.

Snippet below represents the sample code from .NET DLL which contains class with fields:

namespace TestClass
{
	public class TestClass
	{
		public TestClass() { }

        public int PublicValue { get; set; }
        private int PrivateValue { get; }
        public static int StaticValue = 3;
        
        public TestClass(int publicValue, int privateValue)
        {
        	PublicValue = publicValue;
        	PrivateValue = privateValue;
        }
	}
}
public int PublicValue { get; set; }
private int PrivateValue { get; }
public static int StaticValue = 3;

public TestClass(int publicValue, int privateValue)
{
	PublicValue = publicValue;
	PrivateValue = privateValue;
}

It is possible to get one of the declared instance fields from .NET DLL using following C++ code.

#include "Javonet.h"
#include <iostream>
#include <vector>

using namespace JavonetNS::Cpp::Sdk;

std::string resourcesDirectory = ".";

int main(int argc, char* argv[]) {

    // use Activate only once in your app
    Javonet::Activate("your-license-key");
    
    // create called runtime context
    auto calledRuntime = Javonet::InMemory()->Netcore();
    
    // set up variables
    auto libraryPath = resourcesDirectory + "/TestClass.dll";
    auto className = "TestClass.TestClass";
    
    // load custom library
    calledRuntime->LoadLibrary(libraryPath);
    
    // get type from the runtime
    auto calledRuntimeType = calledRuntime->GetType(className)->Execute();
    
    // create type's instance
    auto instance = calledRuntimeType->CreateInstance({ 18,19 })->Execute();
    
    // get instance's field
    auto response = instance->GetInstanceField("PublicValue")->Execute();
    
    // get value from response
    auto result = std::any_cast<int>(response->GetValue());
    
    // write result to console
    std::cout << result << std::endl;
}namespace TestClass
{
	public class TestClass
	{
		public TestClass() { }

        public int PublicValue { get; set; }
        private int PrivateValue { get; }
        public static int StaticValue = 3;
        
        public TestClass(int publicValue, int privateValue)
        {
        	PublicValue = publicValue;
        	PrivateValue = privateValue;
        }
	}
}
// use Activate only once in your app
Javonet::Activate("your-license-key");

// create called runtime context
auto calledRuntime = Javonet::InMemory()->Netcore();

// set up variables
auto libraryPath = resourcesDirectory + "/TestClass.dll";
auto className = "TestClass.TestClass";

// load custom library
calledRuntime->LoadLibrary(libraryPath);

// get type from the runtime
auto calledRuntimeType = calledRuntime->GetType(className)->Execute();

// create type's instance
auto instance = calledRuntimeType->CreateInstance({ 18,19 })->Execute();

// get instance's field
auto response = instance->GetInstanceField("PublicValue")->Execute();

// get value from response
auto result = std::any_cast<int>(response->GetValue());

// write result to console
std::cout << result << std::endl;

This uses in memory runtime bridging to load the .NET DLL, and next retrieves reference to specific type and gets the instance field. Result of the invocation is returned as regular C++ value and can be used for further processing. It is possible to set one of the declared instance fields from .NET DLL using following C++ code.

#include "Javonet.h"
#include <iostream>
#include <vector>

using namespace JavonetNS::Cpp::Sdk;

std::string resourcesDirectory = ".";

int main(int argc, char* argv[]) {

    // use Activate only once in your app
    Javonet::Activate("your-license-key");
    
    // create called runtime context
    auto calledRuntime = Javonet::InMemory()->Netcore();
    
    // set up variables
    auto libraryPath = resourcesDirectory + "/TestClass.dll";
    auto className = "TestClass.TestClass";
    
    // load custom library
    calledRuntime->LoadLibrary(libraryPath);
    
    // get type from the runtime
    auto calledRuntimeType = calledRuntime->GetType(className)->Execute();
    
    // create type's instance
    auto instance = calledRuntimeType->CreateInstance({ 18,19 })->Execute();
    
    // set instance's field
    instance->SetInstanceField("PublicValue", 44)->Execute();
    
    // get instance's field
    auto response = instance->GetInstanceField("PublicValue")->Execute();
    
    // get value from response
    auto result = std::any_cast<int>(response->GetValue());
    
    // write result to console
    std::cout << result << std::endl;
}namespace TestClass
{
	public class TestClass
	{
		public TestClass() { }

        public int PublicValue { get; set; }
        private int PrivateValue { get; }
        public static int StaticValue = 3;
        
        public TestClass(int publicValue, int privateValue)
        {
        	PublicValue = publicValue;
        	PrivateValue = privateValue;
        }
	}
}
// use Activate only once in your app
Javonet::Activate("your-license-key");

// create called runtime context
auto calledRuntime = Javonet::InMemory()->Netcore();

// set up variables
auto libraryPath = resourcesDirectory + "/TestClass.dll";
auto className = "TestClass.TestClass";

// load custom library
calledRuntime->LoadLibrary(libraryPath);

// get type from the runtime
auto calledRuntimeType = calledRuntime->GetType(className)->Execute();

// create type's instance
auto instance = calledRuntimeType->CreateInstance({ 18,19 })->Execute();

// set instance's field
instance->SetInstanceField("PublicValue", 44)->Execute();

// get instance's field
auto response = instance->GetInstanceField("PublicValue")->Execute();

// get value from response
auto result = std::any_cast<int>(response->GetValue());

// write result to console
std::cout << result << std::endl;

This uses in memory runtime bridging to load the .NET DLL, and next retrieves reference to specific type, then sets and gets the instance field. Result of the invocation is returned as regular C++ value and can be used for further processing.

Framework instance fields and properties

The same steps are required to get types and fields from framework .NET DLL:

#include "Javonet.h"
#include <iostream>
#include <vector>

using namespace JavonetNS::Cpp::Sdk;

std::string resourcesDirectory = ".";

int main(int argc, char* argv[]) {

    // use Activate only once in your app
    Javonet::Activate("your-license-key");
    
    // create called runtime context
    auto calledRuntime = Javonet::InMemory()->Netcore();
    
    // get type from the runtime
    auto calledRuntimeType = calledRuntime->GetType("System.DateTime")->Execute();
    
    // create type's instance
    auto instance = calledRuntimeType->CreateInstance({ 2022, 5, 9 })->Execute();
    
    // invoke instance's method
    auto response = instance->GetInstanceField("Year")->Execute();
    
    // get value from response
    auto result = std::any_cast<int>(response->GetValue());
    
    // write result to console
    std::cout << result << std::endl;
}namespace TestClass
{
	public class TestClass
	{
		public TestClass() { }

        // empty
	}
}
// use Activate only once in your app
Javonet::Activate("your-license-key");

// create called runtime context
auto calledRuntime = Javonet::InMemory()->Netcore();

// get type from the runtime
auto calledRuntimeType = calledRuntime->GetType("System.DateTime")->Execute();

// create type's instance
auto instance = calledRuntimeType->CreateInstance({ 2022, 5, 9 })->Execute();

// invoke instance's method
auto response = instance->GetInstanceField("Year")->Execute();

// get value from response
auto result = std::any_cast<int>(response->GetValue());

// write result to console
std::cout << result << std::endl;

The same operation can be performed remotely by just changing the new Runtime Context invocation from in memory to tcp that will create and interact with your .NET DLL objects on any remote node, container or service that hosts Javonet Code Gateway. This way you can preserve the same logic in your application and instantly switch between monolithic and microservices architecture without the need to implement the integration layer based on web services or other remote invocation methods.

Read more about use cases and software architecture scenarios where Javonet runtime bridging technology can support your development process.

Use instance fields and properties from .NET DLL in C++ app

Custom .NET DLL with instance fields and properties

Framework instance fields and properties

Additional references