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Join Date: Apr 2007

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Reputation: obscured47 is an unknown quantity at this point

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obscured47 obscured47 is offline

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Reflection

Nov 12th, 2008

Hi guys,

I have a type that implements an abstract class that is known at compile time and I want to construct at run time an instance of the type and place the reference in a variable that is of the abstract class's type.

So, to describe it a bit.. Say we have 2 class libraries (called A and B). Library A holds the abstract class and library B holds an implementation of the abstract class. A static variable in the abstract class needs to construct at run time a B object and save it in an A type variable... that is, an A type doesn't know about the existance of B on compile time..

So.. I want to read up on app domains and reflection and all those joys of the .NET but don't have the necessary time right now to do it properly so need you guys to guide me a bit on this. Hope it makes (some) sense.

Cheers!

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Join Date: Jun 2005

Posts: 2,039

Reputation: Rashakil Fol is just really nice

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Rashakil Fol Rashakil Fol is offline

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Re: Reflection

Nov 12th, 2008

Pass in to the function in class A a delegate or object that constructs class B.

 Help with Code Tags 
 C# Syntax (Toggle Plain Text) 
abstract class A {
  public static void INeedToConstructSomeSubclass(Func<A> subclassDelegate, ...) {
    A blah = subclassDelegate();
    ...
  }
}
abstract class A {
  public static void INeedToConstructSomeSubclass(Func<A> subclassDelegate, ...) {
    A blah = subclassDelegate();
    ...
  }
}

Then just call it with

 Help with Code Tags 
 C# Syntax (Toggle Plain Text) 
A.INeedToConstructSomeSubclass(() => new B());
A.INeedToConstructSomeSubclass(() => new B());

You'll need some way of communicating which subclass needs to be constructed -- and it's better and more typesafe to pass in a function than something that uses reflection.

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Join Date: Oct 2007

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Reputation: Jugortha is an unknown quantity at this point

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Jugortha

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Re: Reflection

Nov 13th, 2008

Or simply you can use interfaces to play the role of bridge

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Join Date: Aug 2008

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Reputation: LizR has a spectacular aura about

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LizR

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Re: Reflection

Nov 13th, 2008

You can walk through a library looking for classes that descend from something, and then instantiate those.

 Help with Code Tags 
 C# Syntax (Toggle Plain Text) 
            CommandTemplate newcmd;
            Console.Write("Loading commands");
            Assembly a = null;
            AssemblyName n = new AssemblyName("mycmds");
            a = Assembly.Load(n);
            foreach (Type t in a.GetTypes())
            {
 
                if (t.BaseType.Name == "CommandTemplate")
                {
                    newcmd = (CommandTemplate)Activator.CreateInstance(t);
 
                }
            }
            Console.WriteLine(" Done");
            CommandTemplate newcmd;
            Console.Write("Loading commands");
            Assembly a = null;
            AssemblyName n = new AssemblyName("mycmds");
            a = Assembly.Load(n);
            foreach (Type t in a.GetTypes())
            {

                if (t.BaseType.Name == "CommandTemplate")
                {
                    newcmd = (CommandTemplate)Activator.CreateInstance(t);

                }
            }
            Console.WriteLine(" Done");

Did I just hear "You gotta help us, Doc. We've tried nothin' and we're all out of ideas" ? Is this you? Dont let this be you! I will put in as much effort as you seem to.