How do I instantiate a type and its value from a string?

Question

I have code similar to this:

class Foo {     
  Dictionary<Type, Object> _dict;

  void Create(string myType, string myValue)
  {
    var instance = Type.Instanciate(myType)  // How do I do this?
    if (var.IsPrimitive)
    {
      var.GetType().Parse(myValue)   // I know this is there...how to invoke?
      Dictionary[instance.GetType()] = instance;
    }
  }

  T GetValue<T>(T myType) { return (T)_dict[T]; }
}

// Populate with values
foo.Create("System.Int32", "15");
foo.Create("System.String", "My String");
foo.Create("System.Boolean", "False");

// Access a value
bool b = GetValue(b);

So my questions are:
a) How do I instantiate the type
b) Parse the type value from a string when Parse is supported.

Answer 1

• Getting a type: Type.GetType()
• Instantiating a type from a Type object: Activator.CreateInstance (You don't actually need this in your code.)
• Converting from a string: Convert.ChangeType

Note that if the type isn't in mscorlib or the currently executing assembly, you'll need to include the assembly name (and version information if it's strongly named).

Here's a complete example using your original code. Note that GetValue doesn't need a normal parameter, as you've already given the type parameter (T).

using System;
using System.Collections.Generic;

public class Foo {     
  Dictionary<Type, Object> _dict = new Dictionary<Type, Object>();

  public void Create(string myType, string myValue)
  {
      Type type = Type.GetType(myType);
      object value = Convert.ChangeType(myValue, type);
      _dict[type] = value;
  }

  public T GetValue<T>() { return (T)_dict[typeof(T)]; }
}


class Test
{
    static void Main()
    {
        Foo foo = new Foo();

        // Populate with values
        foo.Create("System.Int32", "15");
        foo.Create("System.String", "My String");
        foo.Create("System.Boolean", "False");

        Console.WriteLine(foo.GetValue<int>());
        Console.WriteLine(foo.GetValue<string>());
        Console.WriteLine(foo.GetValue<bool>());
    }
}

Answer 2

a) How do I instantiate the type

You're looking for System.Activator.CreateInstance .

b) Parse the type value from a string when Parse is supported.

You're looking for System.Convert.ChangeType .

Answer 3

using System.Reflection;

public void Create(string myType, string myValue)
{
    Type type = Type.GetType(myType);
    if (type.IsPrimitive)
    {
        MethodInfo Parse = type.GetMethod("Parse");
        Parse.Invoke(null, new object[] { myValue });
        ...
    }
}

Answer 4

You can try Activator.CreateInstance

It has signatures receiving a type and without parameters, or with an array of ojects that while be the parameters

Answer 5

One more thing: keeping a reference to your new instance in the Dictionary could have an unintended consequence: The Dictionary's reference to the object will keep it from ever being collected. If that what you intend, then that's okay, but just be very sure you thing through all the implications of that first.