Dynamically create an object of <Type>

Question

I have a table in my database that I use to manage relationships across my application. it's pretty basic in it's nature - parentType,parentId, childType, childId... all as ints. I've done this setup before, but I did it with a switch/case setup when I had 6 different tables I was trying to link. Now I have 30 tables that I'm trying to do this with and I would like to be able to do this without having to write 30 case entries in my switch command.

Is there a way that I can make reference to a .Net class using a string? I know this isn't valid (because I've tried several variations of this):

Type t = Type.GetType("WebCore.Models.Page");
object page = new t();

I know how to get the Type of an object, but how do I use that on the fly to create a new object?

Answer 1

This link should help:

http://msdn.microsoft.com/en-us/library/system.activator.createinstance(VS.71).aspx

Activator.CreateInstance will create an instance of the specified type.

you could wrap that in a generic method like this:

public T GetInstance<T>(string type)
{
    return (T)Activator.CreateInstance(Type.GetType(type));
}

Answer 2

You want to use Activator.CreateInstance.

Here is an example of how it works:

using System;
using System.Runtime.Remoting;

class Program
{
    static void Main()
    {
     ObjectHandle o = Activator.CreateInstance("mscorlib.dll", "System.Int32");

     Int32 i = (Int32)o.Unwrap();
    }
}

Answer 3

If the type is known by the caller, there's a better, faster way than using Activator.CreateInstance: you can instead use a generic constraint on the method that specifies it has a default parameterless constructor.

Doing it this way is type-safe and doesn't require reflection.

T CreateType<T>() where T : new()
{
   return new T();
}

Answer 4

Assuming you have the following type:

public class Counter<T>
{
  public T Value { get; set; }
}

and have the assembly qualified name of the type, you can construct it in the following manner:

string typeName = typeof(Counter<>).AssemblyQualifiedName;
Type t = Type.GetType(typeName);

Counter<int> counter = 
  (Counter<int>)Activator.CreateInstance(
    t.MakeGenericType(typeof(int)));

counter.Value++;
Console.WriteLine(counter.Value);