using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace _1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void btnSave_Click(object sender, EventArgs e)
        {
            if (this.txtInsert.Text != "")
            {
                this.clbSelect.Items.Add(this.txtInsert.Text);
                this.txtInsert.Clear();
            }
        }

        private void clbSelect_SelectedIndexChanged(object sender, EventArgs e)
        {
            this.txtInsert.AppendText(this.clbSelect.SelectedItem.ToString() + "\r\n");
        }

        private void txtInsert_KeyPress(object sender, KeyPressEventArgs e)
        {
            if(this.txtInsert.Text!="" && e.KeyChar == (char)13)
            {
                e.Handled = true;
                this.clbSelect.Items.Add(this.txtInsert.Text);
                this.txtInsert.Clear();
            }
        }
    }
}

엔터를 치거나 입력을 누르면 입력되고 체크를 하면 텍스트박스에 뜬다.