C# – Activator.CreateInstance can’t find the constructor (MissingMethodException)


I have a class which has the following constructor

public DelayCompositeDesigner(DelayComposite CompositeObject)

    compositeObject = CompositeObject;  

along with a default constructor with no parameters.

Next I'm trying to create an instance, but it only works without parameters:

var designer = Activator.CreateInstance(designerAttribute.Designer);

This works just fine, but if I want to pass parameters it does not:

var designer = Activator.CreateInstance(designerAttribute.Designer, new DelayComposite(4));

This results in an MissingMethodException:

Constructor voor type
was not found

Any ideas here?

The problem is I really need to pass an object during construction.

You see I have a designer which loads all the types that inherit from the CompositeBase. These are then added to a list from which the users can drag them to a designer. Upon doing so an instance of the dragged is added to the designer. Each of these classes have custom properties defined on them:

[CompositeMetaData("Delay","Sets the delay between commands",1)]
public class DelayComposite : CompositeBase

When the user selects an item in the designer, it looks at these attributes in order to load up a designer for that type. For example, in the case of the DelayComposite it would load up a user control which has a label and a slider which allow the user to set the "Delay" property of the DelayComposite instance.

So far this works fine if I don't pass any parameters to the constructor. The designer creates an instance of the DelayCompositeDesigner and assigns it to the content property of a WPF ContentPresenter.

But since that designer needs to modify the properties of the selected DelayComposite
in the designer, I have to pass this instance to it. That is why the constructor looks lie this:

public DelayCompositeDesigner(DelayComposite CompositeObject)

    compositeObject = CompositeObject;

Suggestions are welcome


The result of your code is this:

<—- foo
foo —->

Leppie, you were correct, I had for some reason referenced the Composites assembly in my UI application… which is not something I should have done as I was loading it at runtime. The following code works:

object composite = Activator.CreateInstance(item.CompositType,(byte)205);
                    var designer = Activator.CreateInstance(designerAttribute.Designer, composite);

As you can see the code does not have knowledge of the DelayComposite type.

This solves the current problem, but introduces many new ones for what I want to achieve,
either way thank you and thank you to everyone who has replied here.

As for the following code, suggested by multiple people:

var designer = Activator.CreateInstance(
    new object[] { new DelayComposite(4) } 

The Activator.CreateInstance has a signature that looks like this:

Activator.CreateInstance(Type type, params object[] obj)

So it should accept my code, but I will try the suggested code


I've tried this as suggested:

var designer = Activator.CreateInstance(designerAttribute.Designer, new object[] { new DelayComposite(4)});

The result is the same.

Best Answer

I would think that your call would need to be:

var designer = Activator.CreateInstance(designerAttribute.Designer, new object[] { new DelayComposite(4) });

Unless, of course, it is that, in which case the answer is not immediately obvious.