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3571

answers:

10

I have a class which has the following constructor

public DelayCompositeDesigner(DelayComposite CompositeObject)
{
            InitializeComponent();

            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 Vialis.LightLink.Controller.Scenarios.Composites.DelayCompositeDesigner was not found

Any ideas here?

+2  A: 

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.

DocMax
A: 

I discovered another way of creating an instance of an object without calling the constructor at all while answering another question on SF.

In the System.Runtime.Serialization namespace there is a function FormatterServices.GetUninitializedObject(type) that will create an object without calling constructor.

If you look at that function in Reflector you will see it is making an external call. I don't know how black magic is actually happening under the hood. But I did prove to myself that the constructor was never called but the object was instantiated.

Jason Jackson
A: 

You can use the following overload on CreateInstance:

public static Object CreateInstance(
    Type type,
    Object[] args
)

And in your case it'd be (I think):

var designer = Activator.CreateInstance(
    typeof(DelayCompositeDesigner), 
    new object[] { new DelayComposite(4) } 
);
Kev
I have tried this, but it does not work.Also, it's not required to create a new object[]
TimothyP
A: 

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)]
[CompositeDesigner(typeof(DelayCompositeDesigner))]
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)
{
    InitializeComponent();

    compositeObject = CompositeObject;
}

Suggestions are welcome

TimothyP
A: 

As for the following code, suggested by multiple people:

var designer = Activator.CreateInstance(
    designerAttribute.Designer, 
    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

UPDATE: I've tried this as suggested:

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

The result is the same

TimothyP
+1  A: 

If you want to call this contructor...

public DelayCompositeDesigner(DelayComposite CompositeObject)

...just use this:

var designer = Activator.CreateInstance(typeof(DelayCompositeDesigner), new DelayComposite(4));

or

var designer = Activator.CreateInstance<DelayCompositeDesigner>(new DelayComposite(4));
Ishmaeel
designerAttribute.Designer seems to be =typeof(DelayCompositeDesigner)
VolkerK
Ishmaeel - when he's creating an instance of DelayCompositeDesigner he needs to use the DelayCompositeDesigner(DelayComposite CompositeObject). There isn't an overload on CreateInstance() for the example given.
Kev
Indeed: designerAttribute.Designer is that type, as I have no idea outfront what that will be I cannot use = typeof(DelayCompositeDesigner)
TimothyP
Kev - second argument of CreateInstance is a "params" argument. Which means you can call it with any number of additional arguments without wrapping them in an object[].
Ishmaeel
Kev
What do you mean with OP ?
TimothyP
@TimothyP - Shorthand for Opening Poster, quicker than typing a name.
Kev
+2  A: 

Though I hate printf-like debugging ...

 public static void foo(Type t, params object[] p)
 {
  System.Diagnostics.Debug.WriteLine("<---- foo");
  foreach(System.Reflection.ConstructorInfo ci in t.GetConstructors())
  {
   System.Diagnostics.Debug.WriteLine(t.FullName + ci.ToString());
  }
  foreach (object o in p)
  {
   System.Diagnostics.Debug.WriteLine("param:" + o.GetType().FullName);
  }
  System.Diagnostics.Debug.WriteLine("foo ---->");
 }
// ...
foo(designerAttribute.Designer, new DelayComposite(4));
var designer = Activator.CreateInstance(designerAttribute.Designer, new DelayComposite(4));

What does that print in the visual studio's output window?

VolkerK
A: 

@VolkerK

The result of your code is this:

<---- foo Vialis.LightLink.Controller.Scenarios.Composites.DelayCompositeDesignerVoid .ctor() Vialis.LightLink.Controller.Scenarios.Composites.DelayCompositeDesignerVoid .ctor(Vialis.LightLink.Controller.Scenarios.Composites.DelayComposite) param:Vialis.LightLink.Controller.Scenarios.Composites.DelayComposite foo ---->

TimothyP
+2  A: 

I think you are dealing with a Type mismatch.

Likely the assembly is referenced in different places, or they are compiled against different versions.

I suggest you iterate through the ConstructorInfo's and do a paramtype == typeof(DelayComposite) on the appropriate parameter.

leppie
You might be on to something here.... I'll verify
TimothyP
A: 

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.

TimothyP
Cool :) No problem
leppie