Question

I recently discovered that if I have a form (say from2) which has a public delegate declared in it as such (I know the delegate is not attached to anything)

namespace SomeTest
{
    public partial class Form2 : Form
    {
        public delegate void mydelegate(string some);

        public Form2()
        {   InitializeComponent();}


        private void Form2_Load(object sender, EventArgs e)
        {        }
    }
}

Now if I pass an instance of that form to say another form (form1) as such

namespace SomeTest
{
    public partial class Form1 : Form
    {
        Form2 fm = null;
        public Form1(Form2 fm_)
        {
            this.fm = fm_;
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            //Why cant fm access the public delegate ?
        }
    }
}

Why can’t we go like fm.begininvoke(fm.mydelegate,"SomeParameter") I know the delegate is not attached to something but I am just curious why a public variable is not accessible?

Answer 1

A delegate is a type — that’s why you can access it from the class, but not from an instance. Consider the case of an enum:

public class Foo
{ 
    public enum Bar { A, B, C };
    public Bar Baz;
}

Here Bar is a type, but Baz is an object — so Foo.Bar is valid, but not Foo.Baz. Likewise, if you have an instance var foo = new Foo(); then foo.Bar is invalid, but foo.Baz is ok.

Your delegate type mydelegate is like Bar in this example.

---

If you wanted to add an instance of the delegate:

public partial class Form2
{
    public delegate void mydelegate(string some);
    public mydelegate mydelegateImpl = new mydelegate( arg => Console.WriteLine(arg) );
}

… then you’d be able to access mydelegateImpl from an instance of Form2.