Activator.CreateInstance pass variable to form

Question

I want to pass variables from one form to another.

This is a constructor in form2:

public Form2 (int getId,string getText)

In form1 I'm trying to pass variables like this

var obj = (Form)Activator.CreateInstance(Type.GetType("myproject.Form2"),1,"test");
obj.ShowDialog();

I'm getting error:

Additional information: Constructor on type 'myproject.Form2' not found.

How can I pass a variable?

Is there [a reason](http://meta.stackexchange.com/q/66377/147640) you are using `Activator.CreateInstance` in the first place? — GSerg, Feb 12 '17 at 16:48
Activator only makes sense in the context of dynamic types where you aren't sure at compile time what is the object you will be creating. — Christo S. Christov, Feb 12 '17 at 16:53
You are trying to call Form2's constructor which takes two parameter. The first is parameter of int type and the second is a parameter of string type. According to the error you mentioned, you don't have such constructor in Form2 class. — Jacob, Feb 12 '17 at 16:55

Roman · Accepted Answer · 2017-02-12T18:09:20.177

You should cast to Form2, not to Form.

I don't know where is problem (if you cast to correct type), but if you have corresponding constructor, your code works fine for me.

You can try to pass arguments as object[](object array) - CreateInstance(Type type, object[] args), but also you can pass arguments by the way you pass them (because method accepts params object[] args).

Try to replace this line:

var obj = (Form)Activator.CreateInstance(Type.GetType("myproject.Form2"),1,"test");

by this:

var obj = 
    (Form2)Activator.CreateInstance(Type.GetType("myproject.Form2"), new object[] {1, "test"});

Also, you can use typeof to get Type instance:

var obj = (Form2)Activator.CreateInstance(typeof(Form2), new object[] {1, "test"});

But if you know which type of instance to create at compile time, you should simply create your object using new:

var obj = new Form2(1, "test");

@LuisVito, has it really solved the problem? Because your code is working for me. — Roman, Feb 12 '17 at 17:51

score 2 · Answer 2 · answered Feb 12 '17 at 16:55

As far as my understanding reaches you are misusing the Activator class. What you really should be using is the 'new' keyword to create the object as you are well aware of the type that you will be creating.

Here's how it should look :

var obj = new Form2(1,"test");

Using the Activator class only makes sense when you aren't aware what the type that you will create really is.

score 2 · Answer 3 · edited May 23 '17 at 12:17

Why don't you just create an instance of the Form without using reflection?

Form2 frm2 = new Form2(1, "test");
frm2.ShowDialog();

If you want to use reflection for some reason your code should work provided that the Form2 class is defined within the "myproject" namespace in the same assembly.

namespace myproject
{
    public class Form2 : Form
    {
        public Form2 (int getId, string getText)
        {
            InitializeComponent();
        }
    }
}

If it is defined in another assembly you should read this:

Resolve Type from Class Name in a Different Assembly

Activator.CreateInstance pass variable to form

3 Answers3