How Can I Dynamically Load and Use Methods from a DLL in C# Beyond Assembly.LoadFile()?

Dynamic DLL loading in C#

In C#, developers often need to dynamically load dynamic link libraries (DLLs), especially when using third-party libraries or runtime configurations. This article aims to address the frequently asked questions about the limitations of using the Assembly.LoadFile() method and provide a reflection- and dynamic-object-based solution.

Limitations of Assembly.LoadFile()

As mentioned in the question, using Assembly.LoadFile() successfully loads the DLL and allows information such as the class name to be retrieved. However, it may not be possible to directly call methods in a loaded DLL.

Reflection as a solution

To overcome this limitation, developers can use reflection, which enables dynamic invocation of methods and operation objects at runtime. To do this:

1. Get the Type object of the class: var type = DLL.GetExportedTypes().FirstOrDefault();

2. Create an instance of a class: var c = Activator.CreateInstance(type);

3. Use the InvokeMember() method to call the target method:

    type.InvokeMember("Output", BindingFlags.InvokeMethod, null, c, new object[] { "Hello" });

Dynamic Objects in .NET 4.0

For applications targeting .NET 4.0 or higher, the dynamic keyword can further simplify this process. Using this approach you can access members directly without type reflection:

dynamic c = Activator.CreateInstance(type);
c.Output("Hello");

Conclusion

To summarize, while Assembly.LoadFile() allows loading a DLL, reflection or dynamic objects are required to call methods in the loaded module. Depending on the application's requirements, both methods provide viable solutions for dynamically loading and using DLLs at runtime in C#.

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