To retrieve a IEnuemerable of all types in the current or another Assembly that implement a specific Interface / Abstract class and so on, you can use the snippets below.

Methods

C# Version

Assembly myAssembly = Assembly.LoadFrom(@"C:\Codesnippets.Fesslersoft.de\Fesslersoft.dll");
            
//Gets all referenced Types of the current Assembly that implement a specific interface
IEnumerable<Type> currentAssemblytypes = AppDomain.CurrentDomain.GetAssemblies().SelectMany(x => x.GetTypes()).Where(y => typeof(MyInterfaceName).IsAssignableFrom(y) && !y.IsInterface);
            
//Gets all referenced Types of an assembly that implement a specific interface
IEnumerable<Type> otherAssemblyTypes = myAssembly.GetTypes().Where(y => typeof(MyAbractClassName).IsAssignableFrom(y) && !y.IsInterface);

//You can also change IsInterface to IsAbstract if you are checking for types that implement an Abstract Class.
IEnumerable<Type> otherAssemblyTypesAbstract = myAssembly.GetTypes().Where(y => typeof(MyAbractClassName).IsAssignableFrom(y) && !y.IsAbstract);

VB.NET Version

Dim myAssembly As Assembly = Assembly.LoadFrom("C:\Codesnippets.Fesslersoft.de\Fesslersoft.dll")

'Gets all referenced Types of the current Assembly that implement a specific interface
Dim currentAssemblytypes As IEnumerable(Of Type) = AppDomain.CurrentDomain.GetAssemblies().SelectMany(Function(x) x.GetTypes()).Where(Function(y) GetType(MyInterfaceName).IsAssignableFrom(y) AndAlso Not y.IsInterface)

'Gets all referenced Types of an assembly that implement a specific interface
Dim otherAssemblyTypes As IEnumerable(Of Type) = myAssembly.GetTypes().Where(Function(y) GetType(MyAbractClassName).IsAssignableFrom(y) AndAlso Not y.IsInterface)

'You can also change IsInterface to IsAbstract if you are checking for types that implement an Abstract Class.
 Dim otherAssemblyTypesAbstract As IEnumerable(Of Type) = myAssembly.GetTypes().Where(Function(y) GetType(MyAbractClassName).IsAssignableFrom(y) AndAlso Not y.IsAbstract)

Compatibility: .NET 2.0 .NET 3.0 .NET 3.5 .NET 4.0 .NET 4.5

Do you have an alternate or better method for this task?
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Related links:

• Assembly Class
• AppDomain.GetAssemblies Method
• Assembly.GetTypes Method
• Type.IsInterface Property
• Type.IsAbstract Property