How to create/instantiate an object of 'Type'

Question

I want to iterate through types in an assembly and if a type is a subclass of a specified interface, I want to create an object of the type and add it to a list like so:

var tasks = new List<IScheduledTask>();

foreach (Type t in Assembly.GetExecutingAssembly().GetTypes())
{
    if (t.IsSubclassOf(typeof(IScheduledTask)))
    {
        tasks.Add(new t());
    }
}

Obviously this above does not work. How can you achieve what I am seeking?

George Duckett · Accepted Answer · 2011-06-16T07:49:26.307

4

Activator.CreateInstance is what you're after.

var tasks = new List<IScheduledTask>();
foreach (Type t in Assembly.GetExecutingAssembly().GetTypes())
{
    if (t.IsSubclassOf(typeof(IScheduledTask)))
    {
        tasks.Add((IScheduledTask)Activator.CreateInstance(t));
    }
}

edited Jun 16 '11 at 07:49

answered Jun 15 '11 at 15:56

George Duckett

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This will create a list of objects of type `Object` will it not? – Abe Miessler Jun 15 '11 at 16:01
No, the object will be of type T, you just need to cast it. – Ray Jun 15 '11 at 16:12
@abe-miessler to cast it: `tasks.Add((IScheduledTask)Activator.CreateInstance(t));` – jbtule Jun 15 '11 at 16:23
Ahh, I was thinking he wanted to create an instance of the class that inherits from the interface. If he wanted to do that, would it be possible? – Abe Miessler Jun 15 '11 at 16:24
@Abe-Miessler, that is what `CreateInstance` is doing here. The type given to it is the implementing type, not the interface-type itself. You cast to `IScheduledTask` because you have to in order to put it on your list. – Paul Phillips Jun 15 '11 at 17:00
But doesn't CreateInstance return an object of type `Object`? – Abe Miessler Jun 15 '11 at 17:32
@abe-miessler that's the signature of the method but it's "really" returning an instance of the type it is given. Remember that everything inherits from `Object`. – Paul Phillips Jun 15 '11 at 19:15

score 2 · Answer 2 · answered Jun 15 '11 at 15:58

2

Look at using the Activator.CreateInstance method:

ObjectType instance = (ObjectType)Activator.CreateInstance(objectType);

answered Jun 15 '11 at 15:58

Abe Miessler

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score 1 · Answer 3 · edited May 23 '17 at 11:55

1

This previous question may help Instantiate an object with a runtime-determined type

It uses Activator.CreateInstance

edited May 23 '17 at 11:55

Community

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answered Jun 15 '11 at 15:57

Dean

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score 1 · Answer 4 · answered Jun 15 '11 at 15:58

1

Activator.CreateInstance(t);

will do the trick.

Be careful though, the class you want to instanciate must have a public constructor with no argument for it to work.

answered Jun 15 '11 at 15:58

Falanwe

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How to create/instantiate an object of 'Type'

4 Answers4