Winforms | C# | Autocomplete in the Middle of a Textbox

Customize TextBox autocomplete

Looking at your code you have everything you need but 1 line of code. That line is:

This will only work if the start of a string is entered

//Suggestion only
textBoxName.AutoCompleteMode = AutoCompleteMode.Suggest;
//Suggest and autocomplete
textBoxName.AutoCompleteMode = AutoCompleteMode.SuggestAppend;

This will work as a contains method but works with a custom control

You can also make a custom textbox control that fits your needs.

Custom textbox class:

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();
        this.KeyDown += this_KeyDown;
        this.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.Enter:
            case Keys.Tab:
            {
                if (_listBox.Visible)
                {
                    Text = _listBox.SelectedItem.ToString();
                    ResetListBox();
                    _formerValue = Text;
                    this.Select(this.Text.Length, 0);
                    e.Handled = true;
                }
                break;
            }
            case Keys.Down:
            {
                if ((_listBox.Visible) && (_listBox.SelectedIndex < _listBox.Items.Count - 1))
                    _listBox.SelectedIndex++;
                    e.Handled = true;
                    break;
                }
                case Keys.Up:
                {
                    if ((_listBox.Visible) && (_listBox.SelectedIndex > 0))
                        _listBox.SelectedIndex--;
                    e.Handled = true;
                    break;
                }

            }
        }

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

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

            _formerValue = this.Text;
            string word = this.Text;

            if (_values != null && word.Length > 0)
            {
                string[] matches = Array.FindAll(_values,
                    x => (x.ToLower().Contains(word.ToLower())));
                if (matches.Length > 0)
                {
                    ShowListBox();
                    _listBox.BeginUpdate();
                    _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++)
                        {
                            if (i < 20)
                            _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 : this.Width; ;
                    }
                }
                _listBox.EndUpdate();
            }
            else
            {
                ResetListBox();
            }
        }
        else
        {
            ResetListBox();
        }
    }

    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);
        }
    }
}

Usage:

string[] nameArray = { "name1", "name2", "name3", "bla name" };
AutoCompleteTextBox tb = new AutoCompleteTextBox();
tb.Values = nameArray;
tb.Location = new Point(10,10);
tb.Size = new Size(25,75);
this.Controls.Add( tb );

I got the code for the custom control from: SO Question - Autocomplete contains

How can I get C# textbox autocomplete to make suggestions based on contains rather than starts with?

This is not possible with the built-in TextBox.

Reading the reference source reveals that the AutoComplete feature calls into the native function SHAutoComplete to do it's job. That one does only prefix matching.

You would have to subclass TextBox and provide your own suggestion feature (or purchase one / find an open source one), to do this.

C# WinForms Vertical Alignment for TextBox, etc

If you're turning off AutoSize on a control, it must be a Label, since TextBox doesn't have an AutoSize property. The TextAlign property of a Label is of type ContentAligment, so you can set both horizontal and vertical alignment.

For various boring reasons, TextBoxes in Windows are intended to auto-adjust their heights to the font used. To control the height and vertically center the text, you can quickly create a custom UserControl, that you can use for replacing all your TextBoxes with.

On your UserControl, set the BorderStyle to Fixed3D and the BackColor to System.Window. Add a TextBox and set its BorderStyle to None. In the Resize event for the control, add code that makes the TextBox the same width as the user control's client area (accounting for the border pixels) and left-aligns it (i.e. textBox1.Left = 0;) and vertically centers it (e.g. textBox1.Top = (this.Height - textBox1.Height) / 2;).

Finally, add to the user control any TextBox-type properties and events you need (probably just Text and TextChanged, I would guess), and wire them up so that they pass through to the TextBox inside your control, like this:

public string Text
{
    get => textBox1.Text;
    set => textBox1.Text = value;
}

If you wanted to get super-fancy with this, you could even replace your user control's TextAlign property with one that is actually of type ContentAlignment (like the Label) and then align the inner TextBox to match.

This same approach works for a ComboBox, although it will look slightly odd. With the ComboBox, you set its FlatStyle property to Flat - otherwise you deal with it the same as a TextBox. It will look odd because the drop-down arrow box won't be quite at the top and bottom of the panel.

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