C#

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

namespace WindowsFormsApplication1
{
    public partial class UserControl1 : UserControl
    {
        private DataTable autocompletelist;
        public UserControl1()
        {
            InitializeComponent();

            autocompletelist = new DataTable();
            autocompletelist.Columns.Add("item", typeof(string));
            autocompletelist.DefaultView.Sort = "[item] ASC";
            listBox1.DataSource = autocompletelist;
            listBox1.DisplayMember = "item";
            listBox1.ValueMember = "item";
            listBox1.Visible = false;
            fillautocomplete();// load data in table
            textBox1.TextChanged += textBox1_TextChanged; // wire-up text change handler
            listBox1.DoubleClick += listBox1_DoubleClick; // wire-up double-click handler
            this.Leave += new System.EventHandler(this.UserControl1_Leave);
        }
        private void fillautocomplete()
        {
            // fill the datatable by any means that meets your needs, i.e. a database query
            // for this example I will fill it manually
            autocompletelist.Rows.Add(new object[] { "ape" });
            autocompletelist.Rows.Add(new object[] { "apple" });
            autocompletelist.Rows.Add(new object[] { "apppliance" });
            autocompletelist.Rows.Add(new object[] { "application" });
            autocompletelist.Rows.Add(new object[] { "boy" });
            autocompletelist.Rows.Add(new object[] { "bat" });
        }
        private void textBox1_TextChanged(object sender, System.EventArgs e)
        {
            // note the single quote usage in the filter
            // see: http://msdn.microsoft.com/en-us/library/system.data.datacolumn.expression.aspx
            autocompletelist.DefaultView.RowFilter = "[item] LIKE '" + textBox1.Text + "*'";
            listBox1.Visible = autocompletelist.DefaultView.Count > 0;
        }

        private void listBox1_DoubleClick(object sender, System.EventArgs e)
        {
            if (listBox1.SelectedValue != null)
            {
                textBox1.Text = listBox1.SelectedValue.ToString();
            }
            listBox1.Visible = false;
            textBox1.SelectionStart = textBox1.Text.Length;
            textBox1.Focus();
        }
        public override string Text
        {
            get {return textBox1.Text;}
            set {textBox1.Text = value;}
        }
        private void UserControl1_Leave(object sender, EventArgs e)
        {
            listBox1.Visible = false;
        }
    }
}

// original code by TnTinMn
// modified by bw ... Aug. 21, 2013
private void textBox1_TextChanged(object sender, System.EventArgs e)
{
    // note that for this to work the UserControl must have 'AutoSize set to 'true !

    // * modified by bw ... Aug. 21, 2013
    // quit if the TextBox is empty
    // make sure the ListBox is not visible
    if (string.IsNullOrWhiteSpace(textBox1.Text))
    {
        if (listBox1.Visible) listBox1.Visible = false;
        return;
    }
    //*

    // original code by TnTinMn
    // note the single quote usage in the filter
    // see: http://msdn.microsoft.com/en-us/library/system.data.datacolumn.expression.aspx
    autocompletelist.DefaultView.RowFilter = "[item] LIKE '" + textBox1.Text + "*'";

    // * original code by TnTinMn
    // commented out by bw ... Aug. 21, 2013
    // listBox1.Visible = autocompletelist.DefaultView.Count > 0;
    // *

    // * modified by bw ... Aug. 21, 2013
    if (autocompletelist.DefaultView.Count > 0)
    {
        listBox1.Visible = true;

        // make sure the ListBox expands to shows all possible matches !
        listBox1.Height = (autocompletelist.DefaultView.Count + 1) * listBox1.ItemHeight;
    }
    else
    {
        listBox1.Visible = false;
    }
    //*
}

Quote:

3. your solution will work for a single character entered at the start of a TextBox only.

Quote:

5. if you enter two spaces, followed by a valid letter, like "a" in this case, no choices appear

Member 9901912 wrote:

I think that should exists a template for develop it (with a basic management
of customers, stock, registry of sales and purchases).

Member 3601034 wrote:

I want to implement simple router application using Scocket(tcp)