from a C# method, how to call and run a DLL, where the DLL name comes from a String variable?

Question

I am new to C#.NET. I am writing a method where I need to call and run a DLL file, where the DLL file name comes from a String variable-

String[] spl;

String DLLfile = spl[0];

How do I import this DLL and call a function from the DLL to get the return value? I tried the the following way..

String DLLfile = "MyDLL.dll";

[DllImport(DLLfile, CallingConvention = CallingConvention.StdCall)]

But it did not worked, as The string should be in 'const string' type and 'const string' does not support variables. Please help me with detail procedure. Thanks.

Answer 1

For native DLLs you can create the following static class:

internal static class NativeWinAPI
{
    [DllImport("kernel32.dll")]
    internal static extern IntPtr LoadLibrary(string dllToLoad);

    [DllImport("kernel32.dll")]
    internal static extern bool FreeLibrary(IntPtr hModule);

    [DllImport("kernel32.dll")]
    internal static extern IntPtr GetProcAddress(IntPtr hModule,
        string procedureName);
}

And then use it as follows:

// DLLFileName is, say, "MyLibrary.dll"
IntPtr hLibrary = NativeWinAPI.LoadLibrary(DLLFileName);

if (hLibrary != IntPtr.Zero) // DLL is loaded successfully
{
    // FunctionName is, say, "MyFunctionName"
    IntPtr pointerToFunction = NativeWinAPI.GetProcAddress(hLibrary, FunctionName);

    if (pointerToFunction != IntPtr.Zero)
    {
        MyFunctionDelegate function = (MyFunctionDelegate)Marshal.GetDelegateForFunctionPointer(
            pointerToFunction, typeof(MyFunctionDelegate));
        function(123);
    }

    NativeWinAPI.FreeLibrary(hLibrary);
}

Where MyFunctionDelegate is a delegate. E.g.:

delegate void MyFunctionDelegate(int i);

Answer 2

You can use LoadAssembly method , and CreateInstance method in order to invoke method

        Assembly a = Assembly.Load("example");
        // Get the type to use.
        Type myType = a.GetType("Example");
        // Get the method to call.
        MethodInfo myMethod = myType.GetMethod("MethodA");
        // Create an instance. 
        object obj = Activator.CreateInstance(myType);
        // Execute the method.
        myMethod.Invoke(obj, null);