How do I create an instance from a string in C#?

Question

I'm reading information from an XML which contains the type of an object that I need to instantiate along with it's constructor parameters.

The object type is actually in another project, within a sibling namespace. (I need to create a Company.Project2.Type within Company.Project1 class.)

I found this question, but it doesn't handle the constructor parameters or the fact that it's in another namespace.

How can I do this?

Edit: The assembly name and default namespace wasn't set correctly in the project properties.

Jon Skeet · Accepted Answer · 2009-03-15T17:22:58.077

33

You need to specify the full type name to Type.GetType(), including namespace, e.g. "Company.Project2.Type"
If the type isn't in the same assembly (or mscorlib), you need to give the assembly name too, including version information if it's strongly typed. For example, for a non-strongly typed assembly Company.Project2.dll, you might specify "Company.Project2.Type, Company.Project2".
To call a constructor with parameters you can call Activator.CreateInstance(Type, Object[]) or get the exact constructor you want with Type.GetConstructor() and then call ConstructorInfo.Invoke().

If that doesn't help, please give more information.

edited Mar 15 '09 at 17:22

answered Mar 15 '09 at 17:15

Jon Skeet

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Type.GetType() doesn't seem to find the type with the string I give it. The class Prop is defined in the Reaver.GamePlay namespace, but the returned type is null. – Ben S Mar 15 '09 at 17:27
I've also tried "Reaver.GamePlay.Prop, Reaver.GamePlay" to no avail. – Ben S Mar 15 '09 at 17:32
@Ben: What assembly is it in? Is the assembly strongly typed? – Jon Skeet Mar 15 '09 at 17:59
@JonSkeet I believe it is impossible to use this code to generates String object - since it doesnt have a constructor.(IMHO) .... Can you please provide an alternative for string ? – Royi Namir Aug 03 '12 at 16:03
@RoyiNamir: There are various constructors for `string`. Have a look at MSDN. But in the case of string, it would probably be worth special-casing to just use the string data directly. – Jon Skeet Aug 03 '12 at 16:13
@JonSkeet I meant Default CTOR. ( sorry for not mention it) – Royi Namir Aug 03 '12 at 16:34
@RoyiNamir: Right, there's no parameterless constructor. But this question states: "I'm reading information from an XML which contains the type of an object that I need to instantiate along with it's constructor parameters." – Jon Skeet Aug 03 '12 at 16:35

score 3 · Answer 2 · edited Aug 22 '17 at 17:04

If you want to create a type dynamically at run time, Activator.CreateInstance Method will do it for you. If you issue is with the type having a constructor with parameters, this overload will do this. For example, http://msdn.microsoft.com/en-us/library/wcxyzt4d.aspx

I advise looking through the overloads for the best match.

The namespace issue should be not be relavant - as long as the dll is in the bin directory or the GAC you should be OK. The rules may change if the assembly is Strongly named though.

Could you provide a code snippiet of the code that is not working (using the method you linked to)? This + the errors you are seeing will be very helpful! [update] Quick sample using the Activator.CreateInstance that handles Constructors w/ paramaters.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            BaseProduct b =(BaseProduct)System.Activator.CreateInstance(Type.GetType("ConsoleApplication1.Product")
                ,new object[]{typeof(string)}, 
                new object[]{"123"}
            );
            //Activator..::.CreateInstance Method (Type, array<Object>[]()[], array<Object>[]()[])
        }
    }
    public class Product: BaseProduct{
        public  Product(string id) { 

        }
        public string Id {get;set;}


   }

    public abstract class BaseProduct {
        abstract public string Id { get; set; }
    }
}

How do I create an instance from a string in C#?

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