C # winforms: is my GUI and logic separation doing right?

Edit

Based on the suggestions below for sending logical code GUI delegates, I came up with a code like this:

Action ClearFunction = new Action(()=>Invoke(new Action(delegate() { ResultsBox.Clear(); } ) ));

      

        
        
        
      

    

Can you shorten this?

Here is a portion of my Windows Forms program.

When I started converting the code to use a different thread, it started to feel very brutal when I spawned threads and created public methods wrapped in delegates so that the boolean code could actually use the GUI.

Please provide suggestions for better idioms or architecture improvements. Thanks.

    // form1.cs
    public void ClearResultsBox()
    {
        ResultsBox.Clear();
    }

    public void PrintResults(string s)
    {
        ResultsBox.AppendText(s);
    }

    private void SearchButton_Click(object sender, EventArgs e)
    {
        var t = new Thread(() => SearchCore.Execute(DirectoryBox.Text, SearchBox.Text, this));
        t.Start();
    }

   // logic.cs
class SearchCore
{
    delegate void ClearFunction();
    delegate void AppendFunction(string a);

    static ClearFunction clear;
    static AppendFunction print;

    public static void Execute(string path, string searchterm, MainForm form)
    {
        clear = new ClearFunction(() => form.Invoke(new ClearFunction(form.ClearResultsBox)));
        print = new AppendFunction(s => form.Invoke(new AppendFunction(form.PrintResults), s));

        clear();