Question

How can I register to event and do some actions at runtime?

For example when the user click on a button I want to register to OnMyEvent and run MyFunc that let’s say initialize some textBox with the OnMyEvent args.

I’m using winforms and .NET 4.

EDIT

Maybe I was unclear… I need the ability to register to existing event and add a new method that will run when the event will fire. All at runtime.

EDIT2
i’ll try to give an example…
lets say that i have a class named “A” that have many events OnDataRecived OnDataSend etc…
when the application running the user can choose form a combobox event name to register (i got the events list via reflection because they not constracts, they are generated from xml file) and which data to update when the choosed event is fired.

so for the example the user choose to register to the OnDataReceived and he choose to update property named DataStream. some code…

in run time upon user choosing:

A.OnDataReceived += (s,e) => MyRunTimeMethod(s,e);

private void MyRunTimeMethod(object sender, EventArgs e)  
{
   DataStream = e.Data.Value
}

Answer 1

You are asking how to create a method dynamically at runtime – once you have a reference to that method in a delegate, the question of how to register it to an event is trivial.

MSDN describes how to do this with MSIL instructions. I doubt that’s what you’re looking for, but it is an option.

The C# FAQ blog has a much more interesting solution using expression trees. I suppose this is the one you were referring to by originally tagging your post with expression-tree.

But I would reconsider using dynamic methods at all. How exactly is the user going to specify what action to perform on the event of his choice? I suspect that the options are limited enough that you can get by with something simpler:

protected void btnRegister_Click(object sender, EventArgs e) {
    switch (cmbEvents.SelectedText) {
        case "OnLoad":
            MyControl.OnLoad += (s, e) => SomeSelectedControl.Text = SomeInputControl.Text;
            break;

        //... other cases
    }
}