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?

Pang · Accepted Answer · 2020-10-19 06:41:21Z

73

This link should help:
https://learn.microsoft.com/en-us/dotnet/api/system.activator.createinstance

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));
}

edited Oct 19, 2020 at 6:41

Pang

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answered Feb 23, 2009 at 17:22

Jason Miesionczek

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7 Comments

Andrew Hare Over a year ago

This will not work if the assembly containing the type is not already loaded into the AppDomain.

Andrew Hare Over a year ago

Also in order to call that method then the OP must have access to the type at compile time - the original question asked how to create an instance at execution time from a string.

Jason Miesionczek Over a year ago

i am merely basing my answer on the example provided in the question.

Andrew Hare Over a year ago

Ah you are right - OP does appear to have access to the type! My mistake - (-1) removed!

Jason Miesionczek Over a year ago

Your example would require knowledge of the type at compile time as well :)

|

Guillermo Perez · Accepted Answer · 2018-03-05 15:13:12Z

16

public static T GetInstance<T>(params object[] args)
{
     return (T)Activator.CreateInstance(typeof(T), args);
}

I would use Activator.CreateInstance() instead of casting, as the Activator has a constructor for generics.

edited Mar 5, 2018 at 15:13

Guillermo Perez

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answered Jun 4, 2011 at 15:23

AmuuuInjured

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Comments

Judah Gabriel Himango · Accepted Answer · 2009-02-23 17:28:27Z

15

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();
}

answered Feb 23, 2009 at 17:28

Judah Gabriel Himango

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2 Comments

Jon Skeet Over a year ago

It doesn't require reflection at the source code level - it uses Activator.CreateInstance in the generated IL though.

Jason Miesionczek Over a year ago

reflection is required because the OP specified using a string to identify the Type.

Andrew Hare · Accepted Answer · 2009-02-23 17:29:27Z

8

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();
    }
}

edited Feb 23, 2009 at 17:29

answered Feb 23, 2009 at 17:22

Andrew Hare

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Comments

sduplooy · Accepted Answer · 2009-02-23 17:38:47Z

1

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);

answered Feb 23, 2009 at 17:38

sduplooy

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Comments

Assaf S. · Accepted Answer · 2017-01-19 13:04:17Z

Here is a function I wrote that clones a record of type T, using reflection. This is a very simple implementation, I did not handle complex types etc.

 public static T Clone<T>(T original)
    {
        T newObject = (T)Activator.CreateInstance(original.GetType());

        foreach (var prop in original.GetType().GetProperties())
        {
            prop.SetValue(newObject, prop.GetValue(original));
        }

        return newObject;
    }

I hope this can help someone.

Assaf

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