No overload matches delegate

Question

Thanks to a question previously answered on this website, I've built a little block of code. Unfortunately, I've been getting an error that I don't quite understand. Here's the block of code:

        private void AddTextToUpListBox(string text)
    {
        if (lbxServersThatAreUp.InvokeRequired)
        {
            lbxServersThatAreUp.Invoke(new MethodInvoker(AddTextToUpListBox), new object[] { });
            return;
        }

        lbxServersThatAreUp.Items.Add(text);
    }

The error I'm getting is "No Overload for 'AddTextToUpListBox' matches delegate 'System.Windows.Forms.MethodInvoker'"

So I tried changing the following line like so:

lbxServersThatAreUp.Invoke(new MethodInvoker(AddTextToUpListBox(text)), new object[] { });

but if I do that, it just says "Method name expected". What am I doing wrong here?

Answer 1

MethodInvoker is a delegate with no parameters - you've got a parameter. Two options:

• Use an Action<string>:

  lbxServersThatAreUp.Invoke((Action<string>)AddTextToUpListBox,
                             new object[] { text });
  

• Use a lambda expression to create a MethodInvoker:

  MethodInvoker invoker = () => AddTextToUpListBox(text);
  lbxServersThatAreUp.Invoke(invoker);
  

Answer 2

private void AddTextToUpListBox(string text)
{
    if (lbxServersThatAreUp.InvokeRequired)
    {
        lbxServersThatAreUp.Invoke((Action<String>)AddTextToUpListBox, new object[] { text});
        return;
    }

    lbxServersThatAreUp.Items.Add(text);
}

You need to pass in the parameters for the method, you should also be able to pass the method directly as the delegate.