Instantiate a class from its textual name

Question

Don't ask me why but I need to do the following:

string ClassName = "SomeClassName";  
object o = MagicallyCreateInstance("SomeClassName");

I want to know how many ways there are to do this is and which approach to use in which scenario.

Examples:

Activator.CreateInstance
Assembly.GetExecutingAssembly.CreateInstance("")
Any other suggestions would be appreciated

This question is not meant to be an open ended discussion because I am sure there are only so many ways this can be achieved.

A possible duplicate of http://stackoverflow.com/questions/648160/how-do-i-create-an-instance-from-a-string-in-c — Amritpal Singh, Mar 24 '12 at 19:43
Hmm, what are the odds that you can guess its namespace name correctly? And the assembly it comes from? — Hans Passant, Mar 24 '12 at 19:47
Is the assembly the type is in already loaded or not? If this happens to be something around plugins, you might check out MEF — James Manning, Mar 25 '12 at 04:42
Also, does the class have a no-args ctor? (Specifically, can that be assumed) — James Manning, Mar 25 '12 at 04:43
Actually, these class namespace is known and the classes exist in the same assembly in which I need to do this. — Raheel Khan, Mar 25 '12 at 05:43

Cristian Lupascu · Accepted Answer · 2012-03-25T17:01:10.653

60

Here's what the method may look like:

private static object MagicallyCreateInstance(string className)
{
    var assembly = Assembly.GetExecutingAssembly();

    var type = assembly.GetTypes()
        .First(t => t.Name == className);

    return Activator.CreateInstance(type);
}

The code above assumes that:

you are looking for a class that is in the currently executing assembly (this can be adjusted - just change assembly to whatever you need)
there is exactly one class with the name you are looking for in that assembly
the class has a default constructor

Update:

Here's how to get all the classes that derive from a given class (and are defined in the same assembly):

private static IEnumerable<Type> GetDerivedTypesFor(Type baseType)
{
    var assembly = Assembly.GetExecutingAssembly();

    return assembly.GetTypes()
        .Where(baseType.IsAssignableFrom)
        .Where(t => baseType != t);
}

edited Mar 25 '12 at 17:01

answered Mar 24 '12 at 20:07

Cristian Lupascu

39,078
16
100
137

Exactly what I needed, thanks. I also need to enumerate all classes that derive this class we just created. I'm assuming `assembly.GetTypes` would allow that. – Raheel Khan Mar 25 '12 at 05:47
1

@RaheelKhan I have added a code sample for getting the derived classes defined in the same assembly. – Cristian Lupascu Mar 25 '12 at 17:01
After we got the class, can we call the method inside? – andrefadila Nov 05 '14 at 11:04
@andrefadila Yes. Be aware though that `Activator.CreateInstance` [returns an `object`](http://msdn.microsoft.com/en-us/library/wccyzw83(v=vs.110).aspx) and you may need to cast it first. – Cristian Lupascu Nov 05 '14 at 11:07
Thanks for response @w0lf. So, we must cast it first. Is there any solution without cast? – andrefadila Nov 06 '14 at 03:08
You could also call the method via reflection. (This is pretty hacky) – Cristian Lupascu Nov 06 '14 at 05:08
1

Or you could cast the object not to its exact type, but to an interface that defines that method. – Cristian Lupascu Nov 06 '14 at 05:09
What if the class I want to instantiate is not in the current assembly but lies in the same solution? – Saurabh Shah Mar 23 '18 at 06:29

score 20 · Answer 2 · answered Mar 24 '12 at 20:21

20

Activator.CreateInstance(Type.GetType("SomeNamespace.SomeClassName"));

or

Activator.CreateInstance(null, "SomeNamespace.SomeClassName").Unwrap();

There are also overloads where you can specify constructor arguments.

answered Mar 24 '12 at 20:21

Balazs Tihanyi

6,659
5
23
24

score 0 · Answer 3 · answered Jul 06 '21 at 21:38

0

Use this way to use the class name without the fully qualified namespace:

System.Reflection.Assembly.GetExecutingAssembly().CreateInstance("myclass");

answered Jul 06 '21 at 21:38

AecorSoft

414
4
10

Instantiate a class from its textual name

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