Reflection with Inheritance

Question

I am trying to figure out how to dynamically load a class that inherits another class.  For example, the parent class is:

     internal abstract class Car { }

and the child classes are:

     internal class Ford : Car { }

     internal class Chevy : Car { }

     internal class Jeep : Car { }

Now, let's say that I have a List of cars, like this:

     private List<Car> cars;

and I wanted to add specific makes of cars to that list.  I realize that I can statically load the makes of cars, like this:

     cars.Add( new Ford( ) );

     cars.Add( new Chevy( ) );

     cars.Add( new Jeep( ) );

However, is there any way that I can have an array of strings, like this:

     public String[] carsNames = { "Ford", "Chevy", "Jeep" };

and dynamically load the corresponding Ford, Chevy, and Jeep classes into the cars List, based on the carsNames array?  If there are any good articles or tutorials, please provide the links to them!

Answer 1

Hi, 

You can use Activator.CreateInstance to create object from type or classname

or

by using Assembly.CreateInstance

for your case you can have something like, 

 Array.ForEach(carsNames, f=> cars.Add((Car)Assembly.GetExecutingAssembly().CreateInstance(f))); 

read here about reflection.

I hope this helps you...

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Answer 2

Kriss, this is all ok, I have tried your code, but the indexes in List<T> are created, but all null.

Lets say he hasa class like:

    abstract class Car
    {
        public abstract string Name { get; set; }
        public abstract void ShowName();
    }

and this is an example of Ford class:

    class Ford : Car
    {
        private string carname;
        public Ford(string car)
        {
            this.carname = car;
        }

        public override string Name
        {
            get { return carname; }
            set { this.carname = value; }
        }

        public override void ShowName()
        {
            Console.WriteLine("Ford`s name is {0}.", this.Name);
        }
    }

How you you pass values of string array to each of the class and actually instanitate the class?

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Mitja

Answer 3

@Mitja, in the OP's example all of the classes have default constructors, unlike your example.  In the OPs code the array contains the class's name (unfortunately not fully qualified, so that'll be a part of the problem), not the parameter to initialize it with.

Answer 4

I can see that, but I was just wondering if he/I/you will do it like its my example?

I know its of topic, but still curious how to work it out. 

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Mitja

Answer 5

You can probably come up with ways to do this using reflection. There are a few other actual answers to your question, but instead, I'd suggest you find another way to do this. Reflection should be a last resort, not something to make typing easier. You can solve this without using reflection by introducing a factory pattern. To meet your requirements, I'd do something like this instead:

public static class CarFactory
{
    public static Car CreateCar(string type)
    {
        if (type.Equals("Ford")) return new Ford();
        else if (type.Equals("Chevy")) return new Chevy();
        else if (type.Equals("Jeep")) return new Jeep();
    }
}

public List<Car> ConvertStringArrayToCars(IEnumerable<string> carTypes)
{
    return carTypes.Select(x => CarCreateCar(x)).ToList();
}

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Answer 6

What makes a Ford car different from a Chevy car?

Those differences need to be expressed dynamically in the data (properties) of the class and not from difference of a class objects. The class should allow for a commonality of data storage and processing and not require a class be created based on a name or type.

I believe that the situations needs to be rexamined as to what the atomic base class really is...continuing with the car example, I would change the base class to be a vehicle, then the derived classes from that are car, then truck, followed by a bicycle. Each of the deriveds share a properties such as Name property, then number of wheels...etc.

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William Wegerson (www.OmegaCoder.Com)