Question

I have a problem when trying to raise an event of an object where the type implements an interface (where the event is) form another class.

Here is my code :

The interface IBaseForm

public interface IBaseForm
{
    event EventHandler AfterValidation;
}

The Form that implement the interface IBaseForm

public partial class ContactForm : IBaseForm
{
    //Code ...

    public event EventHandler AfterValidation;
}

My controller : Here where the error occurs

Error message :

The event AfterValidation can only appear on the left hand side of
+= or -=(except when used from whithin the type IBaseForm)

public class MyController
{
    public IBaseForm CurrentForm { get; set; }

    protected void Validation()
    {
        //Code ....

        //Here where the error occurs
        if(CurrentForm.AfterValidation != null)
            CurrentForm.AfterValidation(this, new EventArgs());
    }
}

Thanks in advance

Answer 1

You cannot raise an event from outside of the defining class.

You need to create a Raise() method on your interface:

public interface IBaseForm
{
    event EventHandler AfterValidation;

    void RaiseAfterValidation();
}

public class ContactForm : IBaseForm
{
    public event EventHandler AfterValidation;

    public void RaiseAfterValidation()
    {
        if (AfterValidation != null)
            AfterValidation(this, new EventArgs());
    }
}

And in your controller:

protected void Validation()
{
    CurrentForm.RaiseAfterValidation();
}

But it is usually a design smell if you want to trigger an event from outside the defining class… usually there should be some logic in the IBaseForm implementations which triggers the event.