Can I load a .NET assembly at runtime and instantiate a type knowing only the name?

c# assemblies

Is it possible to instantiate an object at runtime if I only have the DLL name and the class name, without adding a reference to the assembly in the project? The class implements a interface, so once I instantiate the class, I will then cast it to the interface.

Assembly name:

library.dll

Type name:

Company.Project.Classname

EDIT: I dont have the absolute path of the DLL, so Assembly.LoadFile won't work. The DLL might be in the application root, system32, or even loaded in the GAC.

Solution 1:

Yes. You need to use Assembly.LoadFrom to load the assembly into memory, then you can use Activator.CreateInstance to create an instance of your preferred type. You'll need to look the type up first using reflection. Here is a simple example:

Assembly assembly = Assembly.LoadFrom("MyNice.dll");

Type type = assembly.GetType("MyType");

object instanceOfMyType = Activator.CreateInstance(type);

Update

When you have the assembly file name and the type name, you can use Activator.CreateInstance(assemblyName, typeName) to ask the .NET type resolution to resolve that into a type. You could wrap that with a try/catch so that if it fails, you can perform a search of directories where you may specifically store additional assemblies that otherwise might not be searched. This would use the preceding method at that point.

Solution 2:

Consider the limitations of the different Load* methods. From the MSDN docs...

LoadFile does not load files into the LoadFrom context, and does not resolve dependencies using the load path, as the LoadFrom method does.

More information on Load Contexts can be found in the LoadFrom docs.

Solution 3:

Activator.CreateInstance ought to work.

IFace object = (IFace)Activator.CreateInstance( "AssemblyName",
                                                "TypeName" )
                               .Unwrap();

Note: The type name must be the fully qualified type.

Example:

var aray = (IList)Activator.CreateInstance("mscorlib","System.Collections.ArrayList").Unwrap();
aray.Add(10);

foreach (object obj in aray)
{
    Console.WriteLine(obj);
}

Solution 4:

I found this question and some answers very useful, however I did have path problems, so this answer would cover loading library by finding bin directory path.

First solution:

string assemblyName = "library.dll";
string assemblyPath = HttpContext.Current.Server.MapPath("~/bin/" + assemblyName);
Assembly assembly = Assembly.LoadFrom(assemblyPath);
Type T = assembly.GetType("Company.Project.Classname");
Company.Project.Classname instance = (Company.Project.Classname) Activator.CreateInstance(T);

Second solution

string assemblyName = "library.dll";
string assemblyPath = HttpContext.Current.Server.MapPath("~/bin/" + assemblyName);
Assembly assembly = Assembly.LoadFile(assemblyPath);
(Company.Project.Classname) instance = (Company.Project.Classname) assembly.CreateInstance("Company.Project.Classname");

You can use same principle for interfaces (you would be creating a class but casting to interface), such as:

(Company.Project.Interfacename) instance = (Company.Project.Interfacename) assembly.CreateInstance("Company.Project.Classname");

This example is for web application but similar could be used for Desktop application, only path is resolved in different way, for example

Path.GetDirectoryName(Application.ExecutablePath)

Solution 5:

It's Easy.

Example from MSDN:

public static void Main()
{
    // Use the file name to load the assembly into the current
    // application domain.
    Assembly a = Assembly.Load("example");
    // Get the type to use.
    Type myType = a.GetType("Example");
    // Get the method to call.
    MethodInfo myMethod = myType.GetMethod("MethodA");
    // Create an instance.
    object obj = Activator.CreateInstance(myType);
    // Execute the method.
    myMethod.Invoke(obj, null);
}

Here's a reference link

https://msdn.microsoft.com/en-us/library/25y1ya39.aspx