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

namespace multiline_text_suggest
 {
  public partial class Form1 : Form
  {
    ListBox listBox = new ListBox();
    public Form1()
    {
        InitializeComponent();
        Controls.Add(listBox);
        listBox.Hide();
        textsplit();
    }
    string intellisenes;
    private void textsplit() {
        listBox1.Items.Clear();
        foreach (string c in textBox.Text.Split()) {
            listBox1.Items.Add(c);
        }

        intellisenes = listBox1.Items[listBox1.Items.Count-1].ToString().Trim();
    }

    void listBox_SelectedIndexChanged(object sender, KeyEventArgs e)
    {
        if (e.KeyValue == (decimal)Keys.Enter)
        {
            textBox.Text += ((ListBox)sender).SelectedItem.ToString();
            textBox.Focus();
            listBox.Hide();

        }
    }

    private void textBox1_KeyUp(object sender, KeyEventArgs e)
    {
        textsplit();
        listBox.SetBounds(textBox.Left, textBox.Top + textBox.Height, textBox.Width + 20, 40);
        listBox.KeyDown += listBox_SelectedIndexChanged;
        List<string> list = new List<string>(){"king","kong"};
        var localList = list.Where(z => z.StartsWith(intellisenes.Trim())).ToList();
        if (localList.Any() && !string.IsNullOrEmpty(textBox.Text) && !string.IsNullOrWhiteSpace(textBox.Text))
        {
            listBox.DataSource = localList;
            listBox.Show();
            listBox.Focus();
        }

    }

    private void textBox_TextChanged(object sender, EventArgs e)
    {
        textsplit();
    }
}
}