MethodInvoker

Hi

To avoid cross thread issue, I origianlly used the following codes
Form A:
public delegate void GreetingDelegate(string str);
        public void AddGreeting(string str)
        {
            if (this.richTextBox1.InvokeRequired)
            {
                this.richTextBox1.Invoke(new GreetingDelegate(AddGreeting), str);
                return;
            }
            else
            {
                this.richTextBox1.AppendText(str);
            }
        }    
Then I changed the code as follow:
Form B:
private void UpdateUI(MethodInvoker del)
        {
            if(this.InvokeRequired)
                this.Invoke(del);
            else
                del.Invoke();
        }
public void AddGreeting(string str)
        {
            MethodInvoker del = new MethodInvoker(delegate
            {
                this.richtextbx.AppendText(str);
            }
            );
            UpdateUI(del);
        }
When UpdateUI(del) is called, I guess that UpdateUI(del) method does following
Form C:
if(this.InvokeRequired)
{
    this.Invoke((MethodInvoker)(delegate()
                                                {
                                                   this.richtextbx.AppendText(str);
                                                  }
}
else
{
       this.richtextbx.AppendText(str);
 }
What I mean is when UpdateUI(del) is called, I know that it becomes like Form C 'by experience',and I think I understand, why this.Invoke(del) becomes
this.Invoke((MethodInvoker)(delegate()
                                                {
                                                   this.richtextbx.AppendText(str);
                                                  }
Please correct me if I am wrong.
I think the reason is that 'del' is pointing to the "delegate" that executes the anonymouse method and 'this.richtextbx.AppendText(str);' is what anonymous method contains in its body, so it makes sense that it Invoke(del) is like "Hey, I am invoking the delegate you are passing(in this case, it's del)".
 However, I don't understand why del.Invoke() becomes 'this.richtextbx.AppendText(str);'  Can Invoke() method have 0 parameter like this?

Also MethodInvoker is itself a delegate, right?  this delegate execute AddGreeting method.  But msdn says, "MethodInvoker provides a simple delegate that is used to invoke a method with a void parameter list." but AddGreeting has a parameter str.  How can MethodInvoker be used to invoke a method with a parameterlist here?