Agfdhyk

There are three builds in my .net core application.

Solution.Models.Customer:

public class Customer : ICustomer

{           

    public void Get()

    {

        Console.WriteLine("Message!");

    }

}

Solution.Interfaces.ICustomer:

public interface ICustomer

{

    void Get();

}

Solution.Creator.ContainerCreator:

public class ContainerCreator

{

    Assembly _assembly;



    public void Add(Assembly assembly)

    {

        _assembly = assembly;

    }



    public object CreateInstance(Type type)

    {

        object instance;



        var classesInfo = GetClassesInfo();

        //classes Info looks for a match in the assembly with the passed parameter.

        var result = classesInfo.Where(w => w.ClassType.FullName == type.FullName).FirstOrDefault();



        var objectType = result.ClassType;



        instance = Activator.CreateInstance(objectType);



        return instance;

    }

}

Then, when I create an object with the (ICustomer) type, it is successfully created, but if I cast to the (Customer) type, then an exception occurs - System.InvalidCastException.

var files = Directory.GetFiles(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location),

                "Solution.Models.dll",

                SearchOption.TopDirectoryOnly);



var asm = Assembly.LoadFile(files[0]);



ContainerCreator containerCreator = new ContainerCreator();



containerCreator.Add(asm);

// Success

Customer = (ICustomer)containerCreator.CreateInstance(typeof(Customer));

// System.InvalidCastException

//Customer = (Customer)containerCreator.CreateInstance(typeof(Customer));

What am I doing wrong and how can I defeat this exception?

Note:I think OP is trying to create some kind of Plugin stuff. If so, there are many custom libraries for that I suggest you can use already implemented stuff, rather than creating the wheel by yourself

This is a pretty common mistake when people first start to play with assemblies during run time. Been there done that :) The problem is that you are using Assembly.LoadFile to load your assembly into your app-domain. Without going further into detail, even if you load the same dll using Assembly.LoadFile, types defined in the assembly will be treated as differently. Let us say I have assembly A

../MyFolder/A.dll

     public class MyType;

     public class MyAnotherType;

     ....



 var aDll = Assembly.LoadFile("A.dll");

 var aDllAgain = Assembly.LoadFile("A.dll");

 var myTypeFromADll =aDll.GetType("MyType");

 var myTypeFromADllAgain = aDllAgain.GetType("MyType");



 //Yes this is of type MyType but since you used LoadFile

 //It is of type MyType from a_dll code base

 var instanceFromADll = Activator.CreateInstance(myTypeFromADll);



 //Yes this is of type MyType but since you used LoadFile

 //It is of type MyType from a_dll_again code base

 var instanceFromADllAgain = Activator.CreateInstance(myTypeFromADllAgain);

So you are getting an InvalidCastException because you are trying to cast an instance of type X into type Y.

The solution is simple. You should use Assemly.Load method, and somehow if you can not next is Assembly.LoadFrom. Unless you know absolutely what you are doing, stay away from Assembly.LoadFile.

Here is a very good and detailed explanation. Best practices