Dynamic loading DLLs in C #

Remember a long time ago someone asked me to solve such a thing, one of his C dynamic link libraries has a static variable that automatically increases each time the method is invoked, and he wants to restore the dynamic library dynamically and reload it at a particular time, in order to recover the initial value of the static variable. (This dynamic library cannot be changed)

C # Inside to use dynamic library, need to use DllImport, but this is the global thing, not like the dynamic Load/unload assembly use of the AppDomain method.

This is the thought of Api:loadlibrary, GetProcAddress, and FreeLibrary methods.

[DllImport("kernel32",EntryPoint="LoadLibrary",SetLastError=true)]
　static extern IntPtr LoadLibrary(string lpLibName);
　[DllImport("kernel32",EntryPoint="GetProcAddress",SetLastError=true)]
　static extern IntPtr GetProcAddress(IntPtr hModule, string lpProcName);
　[DllImport("kernel32",EntryPoint="FreeLibrary",SetLastError=true)]
　static extern bool FreeLibrary(IntPtr hModule);


and then call

IntPtr hModule = IntPtr.Zero;
　IntPtr pfn = IntPtr.Zero;
　// Load the library and get a pointer to the function　
　hModule = LoadLibrary("ADll.dll");
　pfn = GetProcAddress(hModule, "GetValue");

Then the trouble, know the entry address of this function, how do I call this function, I have not known how to solve this in C #, and finally wrote a section of IL code.

.assembly extern mscorlib {}
.assembly Wrapper {}
.class public Wrapper
{
　　.method public static int32 SomeMethod(native int pfn)
　　{
　　　　.maxstack 2
　　　　.locals (int32 V_0)
　　　　ldarg.0 // Push pfn onto the execution stack
　　　　calli unmanaged stdcall int32()
　　　　stloc.0
　　　　ldloc.0
　　　　ret
　　}
}


Compile this. Il file into a DLL

And then the code goes on to write

// Make call to function pointer
　int i = Wrapper.SomeMethod(pfn);
　MessageBox.Show(this, i.ToString());
　FreeLibrary(hModule);


The problem is solved.