MissingMethodException when creating an object with reflection

Question

I'm using reflection to create objects coming from an external assembly. My problem is that I cannot create an object that way:

Type t = assembly.GetType("ExternalClass");
object obj = Activator.CreateInstance(t, new object[] { data, Type.Missing, Type.Missing });

I get System.MissingMethodException: Additional information: Constructor on type 'ExternalClass' not found. However everything works fine using that way:

Type t = assembly.GetType("ExternalClass");
ConstructorInfo[] constructors = t.GetConstructors();
object obj = constructors[0].Invoke(new object[] { data, Type.Missing, Type.Missing });

ExternalClass has only 1 constructor with 2 optional parameters and I'm sure I'm passing correct arguments, because the second way creates the object I want. Do I miss something in the first approach? I would prefer the first one, because it's easier to read

EDIT: I forgot about CultureInfo (why would this method need it?!). The solution is to use:

object obj = Activator.CreateInstance(t,
    BindingFlags.CreateInstance |
    BindingFlags.Public |
    BindingFlags.Instance |
    BindingFlags.OptionalParamBinding, null, new object[] { data, Type.Missing, Type.Missing }, CultureInfo.CurrentCulture);

How should I invoke CreateInstance using BindingFlags.OptionalParamBinding? Maybe that's the problem — YogoWafel
– YogoWafel, Commented Feb 17, 2018 at 18:46

Johnny · Accepted Answer · 2018-02-17 19:00:08Z

3

This is the way how you should construct the constructor with the Activator

(T)Activator.CreateInstance(typeof(T), 
    BindingFlags.CreateInstance |
    BindingFlags.Public |
    BindingFlags.Instance |
    BindingFlags.OptionalParamBinding, null, new object[] { data, Type.Missing, Type.Missing }, CultureInfo.CurrentCulture);

answered Feb 17, 2018 at 19:00

Johnny

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2 Comments

YogoWafel Over a year ago

Great! That worked, thank you! Btw, I still wonder, why would CreateInstance need CultureInfo...

Johnny Over a year ago

Good question can be next question on stackoverflow is still doesn't exist, I could not find the real usage...

Lennart Stoop · Accepted Answer · 2018-02-17 19:02:43Z

0

You can do so by adding the appropriate binding flags, for example:

(T)Activator.CreateInstance(typeof(T), 
                BindingFlags.CreateInstance |
                BindingFlags.Public |
                BindingFlags.Instance | 
                BindingFlags.OptionalParamBinding,
                null,
                new object[] {data, Type.Missing, Type.Missing },
                CultureInfo.CurrentCulture);

edited Feb 17, 2018 at 19:02

answered Feb 17, 2018 at 18:45

Lennart Stoop

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3 Comments

YogoWafel Over a year ago

nope, I still get Constructor on type 'ExternalClass' not found. with that approach

YogoWafel Over a year ago

Strange thing is, that despite copying your code, Visual Studio gives me the previous overload tip when I point cursor at the method - why can't I see the BindingGlags in its parameters? link

Lennart Stoop Over a year ago

Yeah I was just looking at the overloads, it also takes a culture, I'll edit the snippet

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