WinForms | C# | AutoComplete in the Middle of a Textbox?

Question

I have a textbox that does autocompletion like so:

txtName.AutoCompleteMode = AutoCompleteMode.Suggest;
txtName.AutoCompleteSource = AutoCompleteSource.CustomSource;
txtName.AutoCompleteCustomSource = namesCollection;

It works, but only at the beginning of a textbox. I'd like autocomplete to kick in for any word the user is entering, at any position in the textbox.

Answer 1

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Windows.Forms;

namespace TubeUploader
{
    public class AutoCompleteTextBox : TextBox
    {
        private ListBox _listBox;
        private bool _isAdded;
        private String[] _values;
        private String _formerValue = String.Empty;

        public AutoCompleteTextBox()
        {
            InitializeComponent();
            ResetListBox();
        }

        private void InitializeComponent()
        {
            _listBox = new ListBox();
            KeyDown += this_KeyDown;
            KeyUp += this_KeyUp;
        }

        private void ShowListBox()
        {
            if (!_isAdded)
            {
                Parent.Controls.Add(_listBox);
                _listBox.Left = Left;
                _listBox.Top = Top + Height;
                _isAdded = true;
            }
            _listBox.Visible = true;
            _listBox.BringToFront();
        }

        private void ResetListBox()
        {
            _listBox.Visible = false;
        }

        private void this_KeyUp(object sender, KeyEventArgs e)
        {
            UpdateListBox();
        }

        private void this_KeyDown(object sender, KeyEventArgs e)
        {
            switch (e.KeyCode)
            {
                case Keys.Tab:
                    {
                        if (_listBox.Visible)
                        {
                            InsertWord((String)_listBox.SelectedItem);
                            ResetListBox();
                            _formerValue = Text;
                        }
                        break;
                    }
                case Keys.Down:
                    {
                        if ((_listBox.Visible) && (_listBox.SelectedIndex < _listBox.Items.Count - 1))
                            _listBox.SelectedIndex++;

                        break;
                    }
                case Keys.Up:
                    {
                        if ((_listBox.Visible) && (_listBox.SelectedIndex > 0))
                            _listBox.SelectedIndex--;

                        break;
                    }
            }
        }

        protected override bool IsInputKey(Keys keyData)
        {
            switch (keyData)
            {
                case Keys.Tab:
                    return true;
                default:
                    return base.IsInputKey(keyData);
            }
        }

        private void UpdateListBox()
        {
            if (Text == _formerValue) return;
            _formerValue = Text;
            String word = GetWord();

            if (_values != null && word.Length > 0)
            {
                String[] matches = Array.FindAll(_values,
                                                 x => (x.StartsWith(word, StringComparison.OrdinalIgnoreCase) && !SelectedValues.Contains(x)));
                if (matches.Length > 0)
                {
                    ShowListBox();
                    _listBox.Items.Clear();
                    Array.ForEach(matches, x => _listBox.Items.Add(x));
                    _listBox.SelectedIndex = 0;
                    _listBox.Height = 0;
                    _listBox.Width = 0;
                    Focus();
                    using (Graphics graphics = _listBox.CreateGraphics())
                    {
                        for (int i = 0; i < _listBox.Items.Count; i++)
                        {
                            _listBox.Height += _listBox.GetItemHeight(i);
                            // it item width is larger than the current one
                            // set it to the new max item width
                            // GetItemRectangle does not work for me
                            // we add a little extra space by using '_'
                            int itemWidth = (int)graphics.MeasureString(((String)_listBox.Items[i]) + "_", _listBox.Font).Width;
                            _listBox.Width = (_listBox.Width < itemWidth) ? itemWidth : _listBox.Width;
                        }
                    }
                }
                else
                {
                    ResetListBox();
                }
            }
            else
            {
                ResetListBox();
            }
        }

        private String GetWord()
        {
            String text = Text;
            int pos = SelectionStart;

            int posStart = text.LastIndexOf(' ', (pos < 1) ? 0 : pos - 1);
            posStart = (posStart == -1) ? 0 : posStart + 1;
            int posEnd = text.IndexOf(' ', pos);
            posEnd = (posEnd == -1) ? text.Length : posEnd;

            int length = ((posEnd - posStart) < 0) ? 0 : posEnd - posStart;

            return text.Substring(posStart, length);
        }

        private void InsertWord(String newTag)
        {
            String text = Text;
            int pos = SelectionStart;

            int posStart = text.LastIndexOf(' ', (pos < 1) ? 0 : pos - 1);
            posStart = (posStart == -1) ? 0 : posStart + 1;
            int posEnd = text.IndexOf(' ', pos);

            String firstPart = text.Substring(0, posStart) + newTag;
            String updatedText = firstPart + ((posEnd == -1) ? "" : text.Substring(posEnd, text.Length - posEnd));


            Text = updatedText;
            SelectionStart = firstPart.Length;
        }

        public String[] Values
        {
            get
            {
                return _values;
            }
            set
            {
                _values = value;
            }
        }

        public List<String> SelectedValues
        {
            get
            {
                String[] result = Text.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
                return new List<String>(result);
            }
        }

    }

}

Sample Usage

using System;
using System.Windows.Forms;

namespace AutoComplete
{
    public partial class TestForm : Form
    {
        private readonly String[] _values = { "one", "two", "three", "tree", "four", "fivee" };

        public TestForm()
        {
            InitializeComponent();
            // AutoComplete is our special textbox control on the form
            AutoComplete.Values = _values;
        }

    }
}