How to get a string name to resolve to an object (i.e. in the sense of what it is)

Question

For example I can do something like:

switch (myString)
case "rectangle":
 o = new rect();
 break;
case "ellipse"
 etc...

but how do I not do the above, i.e. just have one line of code that gets the object directly from the string. Imagine, for example, a button and whatever it says when the user clicks it, it takes the displayed text and creates an object from it.

Answer 1

If the name is the exact same thing as the string, you can do something like this:

using System;
using System.Reflection;

class Example
{
    static void Main()
    {
        var assemblyName = Assembly.GetExecutingAssembly().FullName;
        var o = Activator.CreateInstance(assemblyName, "Example").Unwrap();
    }
}

A simpler approach would look like this:

using System;
using System.Reflection;

class Example
{
    static void Main()
    {
        var type = Assembly.GetExecutingAssembly().GetType("Example");
        var o = Activator.CreateInstance(type);
    }
}

But keep in mind that this is a very simple example that doesn't involve namespaces, strong-named assemblies, or any other complicated things that crop up in bigger projects.

Answer 2

Check Activator.CreateInstace(Type) or Activator.CreateInstance(string, string)

Answer 3

He descf,

Have you tried Activator.CreateInstace("assemblyname", "typename");

Answer 4

A Factory pattern would decouple the code from the string. Please take a look at this dofactory page for both the UML and a C# example of the Factory pattern.