How to dynamically cast an object of type string to an object of type T

Question

I have this XML document

<AdditionalParameters>
<PublishToPdf Type ="System.Boolean">False</PublishToPdf>
</AdditionalParameters>

in my code and I'm trying to build an array of arguments containing the <PublishToPdf> node.

object test = (object) ((typeof(publishNode.Attributes["Type"].value)) publishNode.InnerText);

This breaks at compile time of course. I can't figure out how to cast the publishNode.InnerText('false') to a runtime defined object of type specified in the XML file and store it in an object (which will conserve the type).

score 28 · Accepted Answer · answered Sep 23 '09 at 13:14

28

You can use Convert.ChangeType :

object value = Convert.ChangeType(stringValue, destinationType);

answered Sep 23 '09 at 13:14

Thomas Levesque

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Yes, and to get destinationType, use var destinationType = Type.Parse(publishNode.Attributes["Type"].value); – Digitalex Sep 23 '09 at 13:20
1

Type.Parse() doesn't seem to exist. Did you mean Type.GetType() by any chance? – Paul McLean Jun 18 '14 at 05:42

score 3 · Answer 2 · answered Sep 23 '09 at 13:08

You can't do exactly what you're trying to do. First, the typeof keyword does not allow for dynamic evaluation at runtime. There are means by which to do this using reflection, with methods like Type.GetType(string), but the Type objects returned from these reflective functions can't be used for operations like casting.

What you need to do is provide a means of converting your type to and from a string representation. There is no automatic conversion from any arbitrary type. For your example, you can use bool.Parse or bool.TryParse, but those are specific to the bool type. There are similar methods on most primitive types.

score 1 · Answer 3 · answered Sep 23 '09 at 13:17

1

The simple solution, assuming there is a limited number of possible types;

object GetValueObject(string type, string value)
{
  switch (type)
  {
    case "System.Boolean":
      return Boolean.Parse(value);
    case "System.Int32":
      return Int32.Parse(value);
    ...
    default:
      return value;
  }
}  

var type = publishNode.Attributes["Type"].value;
var value = publishNode.InnerText;
var valueObject = GetValueObject(type, value);

answered Sep 23 '09 at 13:17

Digitalex

1,494
9
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i'm working with .net framework 2.0. and i don't have var. And the solution you suggested is the factory implementing the creation of objets of all types, which are countless. But thanks for your help anyway. – LolaRun Sep 23 '09 at 13:20
Well, the var was just to make the code shorter, u can use string, string, object for these three instead. And, as I said, if you only need to support a limited number of types, this would work fine. If not, then you're right to say it's not practical. – Digitalex Sep 23 '09 at 13:35
1

With C# 6 you can use `case nameof(System.Guid):` for example. No need for const strings anymore. nameof is compile time generated. – Mike de Klerk Oct 07 '16 at 09:35

How to dynamically cast an object of type string to an object of type T

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