Invoke Constructor method of any class that extends an Interface without having to specifically cast each class

[Jost Pedro]

Hi guys, I have a class that extends an IMenuProvider interface and belongs to a plug-in project. In the UI project(other project) I've developed a menuService class that finds plug-ins that implement a IMenuProvider interface and execute the constructor method by using the invoke method. Here's the code.

...

 Type[] types = assembly.GetTypes();
            foreach (Type type in types)
            {
                if (type.GetInterface("IMenuProvider") != null)
                {
                    if (!ht.ContainsKey(type.FullName))
                    {
                        //get construct info.
                        ConstructorInfo cinfo = type.GetConstructor(System.Type.EmptyTypes);
                        
                        //invoke constructor 
                        IMenuProvider imp = (IMenuProvider)cinfo.Invoke(null);  **
                        ht.Add(type.FullName, imp);
                        RegisterProvider(imp);
                    }
                }
            } 
...

So what happens is the line marked with ** returns an error saying "Unable to cast object of type 'TestPlugin.PluginMenuProvider' to type 'Enki.UI.ComponentModel.IMenuProvider'." I know that I’m attempting to invoke the constructor method of the subclass PluginMenuProvider through the extension IMenuProvider but i don’t want to have to specify every subclass that extends the IMenuProvider interface. Now, my question is how can i invoke the constructor without having to declare and than cast each class type that extends the interface IMenuProvider like the line marked with ** does? Best regards. Pedro M.

[led mike]

Jost Pedro wrote:

execute the constructor method by using the invoke method

Invoking constructors might have a place but I would avoid it. From a design perspective I would use a Creational Design Pattern.

led mike

[MGoettmann]

Pedro, have a look at Plug-ins and cast exceptions [^]. Martin

[S Senthil Kumar]

How about simply using Activator.CreateInstace[^] instead, especially considering that the constructor doesn't take any parameters? That's the typical way in which objects are created using reflection.

Type[] types = assembly.GetTypes();             foreach (Type type in types)             {                 if (type.GetInterface("IMenuProvider") != null)                 {                     if (!ht.ContainsKey(type.FullName))                     {                          IMenuProvider imp = (IMenuProvider)Activator.CreateInstance(type);
                         ...

Regards Senthil [MVP - Visual C#] _____________________________ My Blog | My Articles | WinMacro