can anyone tell me the working principle of external assebly in c#.net?

What do you mean by external assembly?? if you mean a dll, it just a methodology to keep some related functions in assembly to be reusable by many different applications.

External assemblies come in two flavors. Referenced (required at startup), and dynamically loaded at some point when the program wants to use some feature within the external assembly. Dynamically loading and managing assemblies is not automatic. You have to write code to manage these external assemblies.

If this isn't very clear, then search on Google for "C# Plugin", and you will find ample information on the subject. (over 6mil refs)

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