Plugin based application in C#

Question

I have to make a graphical user interface application using the language of my choice. The application will run on Windows XP. It will be some sort of a complex windows form application. I think and as per most suggestions, C# will be the best to use. The tree structure on the left of the GUI will populate after reading from a configuration file which will be a binary file . (but initially I can work with a simple ASCII file to test my code.). The application will accept some inputs from the user through this GUI and will write the back to the same config file and will reflect the changes in the tree structure or the labels or any other pertaining field on the form.

There will be 3 tabs and 3 corresponding config files for each of the tabs. I need some help designing the application for now. I am planning to make a host application (main application) and use the 3 tab controls as plugins. Is this workable ? If so can you please guide me on this. I mean how do I make 3 plugins in C# and how do I write the interfaces so that the main application knows which plugin to load and when to load it ? Will there be a separate “Plugin” folder under my project folder ? I hope you got my point though this is too little of an information for you to begin with.

Also there are some .cpp files already existing in the project. These files along with some .h files contain some important definitions and constants in them. These need to be integrated with my C# application. I have no clue how to do that but I am sure that it is possible by compiling the .cpp code in a .dll and then exposing the compiled .dll to my C# application. Please let me know if you need some more information for the top level design.

Thanks, Viren

Answer 1

To implement a plugin interface manually, you will need a method something like this. I've left some TODOs in, where you would want to enhance the error handling and/or make the implementation a little more case specific.

    public List<T> LoadPlugin<T>(string directory)
    {
        Type interfaceType = typeof(T);
        List<T> implementations = new List<T>();

        //TODO: perform checks to ensure type is valid

        foreach (var file in System.IO.Directory.GetFiles(directory))
        {
            //TODO: add proper file handling here and limit files to check
            //try/catch added in place of ensure files are not .dll
            try
            {
                foreach (var type in System.Reflection.Assembly.LoadFile(file).GetTypes())
                {
                    if (interfaceType.IsAssignableFrom(type) && interfaceType != type)
                    { 
                        //found class that implements interface
                        //TODO: perform additional checks to ensure any
                        //requirements not specified in interface
                        //ex: ensure type is a class, check for default constructor, etc
                        T instance = (T)Activator.CreateInstance(type);
                        implementations.Add(instance);
                    }
                }
            }
            catch { }
        }

        return implementations;
    }

Example to call:

List<IPlugin> plugins = LoadPlugin<IPlugin>(path);

As for the c++ part of your question. There are few different ways you could approach this, though the correct choice depends on your specific situation. You can make a clr compliant .dll in c++, which your c# project could reference and call like any other .dll it references. Additionally, you could use P/Invoke to call into a native .dll.