} public partial class MainFrm: Form ... { private void MainFrm _Load(object sender, EventArgs e) ...{ Middle.sendEvent += new Middle.SendMessage(this.DoMethod); } public void DoMethod(string getstr) ...{ listBox1.Items.Add(getstr); }} ChildFrm.cs: public partial class ChildFrm: Form ... { public ChildFrm () ...{ InitializeComponent(); } private void button1_Click(object sender, EventArgs e) ...{ Middle.DoSendMessage(this.textBox1.Text); textBox1.Text = ""; textBox1.Focus(); } } Middle.cs: public static class Middle ... { public delegate void SendMessage(string str); public static event SendMessage sendEvent; public static void DoSendMessage(string str) ...{ sendEvent(str); }}