Dynamically invoke a method in DLL

Question

I have a DLL containing some methods (show, hide and validate). Here is an example of one of the methods hide(Panel paneldynamic, String id, List<EventActions> eventList). All methods contains the same parameters.

Now I have referenced the my DLL on my main form, how can I dynamically invoke one of the methods at runtime?

Answer 1

You'll need to use reflection. First, load the assembly (note that this assumes you've imported System.Reflection):

Assembly a = Assembly.LoadFile(pathToTheDll);

Get the type containing the method by fully-qualified name:

Type t = a.GetType("Some.Class");

Now, get the method:

MethodInfo m = t.GetMethod("hide"); // For example

Then, all you have to do is invoke it:

m.Invoke(null, new object[] { /* parameters go here */ });

The first argument to Invoke is the instance. If your class is static, use null, otherwise, you'll need to supply an instance of the type created using Assembly.CreateInstance.

Answer 2

Insert your methods as delegates into a dictionary

public enum MethodType
{
    None,
    Show,
    Hide,
    Validate
}

var methods = new Dictionary<MethodType, Action<Panel, String, List<EventActions>>();
methods.Add(MethodType.Show, show);
methods.Add(MethodType.Hide, hide);
methods.Add(MethodType.Validate, validate);

Then you can invoke one of them with

MethodType methodToInvoke = MethodType.Hide;
methods[methodToInvoke](paneldynamic, id, eventList);

---

If you intend to dynamically load the DLL, this is another story. You will need at least three assemblies (three projects): one main assembly (exe), one contract assembly (dll) and one plug-in assembly (dll). The main and the plug-in assembly both have to reference the contract assembly. The contract assembly contains an interface

public interface IPlugIn
{
    void Show(Panel paneldynamic, String id, List<EventActions> eventList);
    void Hide(Panel paneldynamic, String id, List<EventActions> eventList);
    void Validate(Panel paneldynamic, String id, List<EventActions> eventList);
}

The plug-in assembly contains a class implementing the interface

public class PlugIn : IPlugIn
{
    // TODO: implement IPlugIn
}

In the main assembly you can load the plug-in like this

IPlugIn LoadPlugInFromFile(string fileName)
{
    Assembly asm = Assembly.LoadFrom(fileName);
    Type type = asm.GetType("PlugIn");
    IPlugIn plugIn = (IPlugIn)Activator.CreateInstance(type);
    return plugIn;
}

Invoke like this

IPlugIn plugIn = LoadPlugInFromFile("C:\PlugIns\MyPlugIn.dll");
plugIn.Show(paneldynamic, id, eventList);