Loading DLLs at runtime in C

Question

I am trying to figure out how you could go about importing and using a  dll at runtime inside a C  application  Using Assembly LoadFile   I have managed to get my program to load the dll  this part is definitely working as I am able to get the name of the class with ToString     however I am unable to use the  Output  method from inside my console application  I am compiling the  dll then moving it into my console s project  Is there an extra step between CreateInstance and then being able to use the methods   This is the class in my DLL   namespace DLL       using System       public class Class1               public void Output string s                        Console WriteLine s                       and here is the application I want to load the DLL  namespace ConsoleApplication1       using System      using System Reflection       class Program               static void Main string   args                        var DLL   Assembly LoadFile   C  visual studio 2012 Projects ConsoleApplication1 ConsoleApplication1 DLL dll                 foreach Type type in DLL GetExportedTypes                                  var c   Activator CreateInstance type                   c Output   Hello                               Console ReadLine

User · Answer

It s not so difficult    You can inspect the available functions of the loaded object  and if you find the one you re looking for by name  then snoop its expected parms  if any  If it s the call you re trying to find  then call it using the MethodInfo object s Invoke method   Another option is to simply build your external objects to an interface  and cast the loaded object to that interface  If successful  call the function natively    This is pretty simple stuff

User · Answer

Right now  you re creating an instance of every type defined in the assembly   You only need to create a single instance of Class1 in order to call the method   class Program       static void Main string   args                var DLL   Assembly LoadFile   C  visual studio 2012 Projects ConsoleApplication1 ConsoleApplication1 DLL dll             var theType   DLL GetType  DLL Class1            var c   Activator CreateInstance theType           var method   theType GetMethod  Output            method Invoke c  new object     Hello              Console ReadLine

User · Answer

You need to create an instance of the type that expose the Output method   static void Main string   args                var DLL   Assembly LoadFile   C  visual studio 2012 Projects ConsoleApplication1 ConsoleApplication1 DLL dll             var class1Type   DLL GetType  DLL Class1               Now you can use reflection or dynamic to call the method  I will show you the dynamic way          dynamic c   Activator CreateInstance class1Type           c Output   Hello             Console ReadLine

User · Answer

foreach  var f in Directory GetFiles  quot   quot    quot   dll quot                Assembly LoadFrom f    That loads all the DLLs present in your executable s folder  In my case I was trying to use Reflection to find all subclasses of a class  even in other DLLs  This worked  but I m not sure if it s the best way to do it  EDIT  I timed it  and it only seems to load them the first time  Stopwatch stopwatch   new Stopwatch    for  int i   0  i  lt  4  i          stopwatch Restart        foreach  var f in Directory GetFiles  quot   quot    quot   dll quot            Assembly LoadFrom f       stopwatch Stop        Console WriteLine stopwatch ElapsedMilliseconds      Output  34 0 0 0 So one could potentially run that code before any Reflection searches just in case

User · Answer

Members must be resolvable at compile time to be called directly from C   Otherwise you must use reflection or dynamic objects   Reflection  namespace ConsoleApplication1       using System      using System Reflection       class Program               static void Main string   args                        var DLL   Assembly LoadFile   C  visual studio 2012 Projects ConsoleApplication1 ConsoleApplication1 DLL dll                 foreach Type type in DLL GetExportedTypes                                  var c   Activator CreateInstance type                   type InvokeMember  Output   BindingFlags InvokeMethod  null  c  new object      Hello                                Console ReadLine                        Dynamic   NET 4 0   namespace ConsoleApplication1       using System      using System Reflection       class Program               static void Main string   args                        var DLL   Assembly LoadFile   C  visual studio 2012 Projects ConsoleApplication1 ConsoleApplication1 DLL dll                 foreach Type type in DLL GetExportedTypes                                  dynamic c   Activator CreateInstance type                   c Output   Hello                               Console ReadLine

User · Answer

Activator CreateInstance   returns an object  which doesn t have an Output method   It looks like you come from dynamic programming languages  C  is definetly not that  and what you are trying to do will be difficult   Since you are loading a specific dll from a specific location  maybe you just want to add it as a reference to your console application   If you absolutely want to load the assembly via Assembly Load  you will have to go via reflection to call any members on c  Something like type GetMethod  Output   Invoke c  null   should do it

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