This other SO question asks about an autocomplete textbox in WPF. Several people have

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Asked: May 13, 20262026-05-13T20:58:48+00:00 2026-05-13T20:58:48+00:00

This other SO question asks about an autocomplete textbox in WPF. Several people have

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This other SO question asks about an autocomplete textbox in WPF. Several people have built these, and one of the answers given there suggests this codeproject article.

But I’ve not found any WPF Autocomplete Textbox that compares with the WinForms autocomplete textbox. The codeproject sample works, sort of, …

…but

it isn’t structured as a re-usable control or DLL. It’s code I need to embed in every app.
It works only with directories. it doesn’t have properties for setting whether the autocomplete source is filesystem directories only, or filesystem files, or ….etc. I could write code to do this, of course, but…I’d rather use someone else’s code already written.
it doesn’t have properties to set the popup size, etc.
there’s a popup listbox that presents the posible completions. When navigating through that list, the textbox doesn’t change. Typing a character while focused in the listbox doesn’t cause the textbox to get updated.
navigating focus away from the listbox doesn’t make the popup listbox disappear. This is confusing.

So, my question:

*Does anyone have a FREE WPF AutoComplete textbox that works, and provides a quality UI experience?*

ANSWER

Here’s how I did it:

.0. get the WPF Toolkit

.1. run the MSI for the WPF Toolkit

.2. Within Visual Studio, Drag/drop from the toolbox – specifically the Data Visualization group – into the UI Designer. It looks like this in the VS toolbox:

If you don’t want to use the designer, hand-craft the xaml. It looks like this:

<toolkit:AutoCompleteBox
   ToolTip="Enter the path of an assembly."
   x:Name="tbAssembly" Height="27" Width="102"
   Populating="tbAssembly_Populating" />

…where the toolkit namespace is mapped this way:

xmlns:toolkit="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Input.Toolkit"

.3. Provide the code for the Populating event. Here’s what I used:

private void tbAssembly_Populating(object sender, System.Windows.Controls.PopulatingEventArgs e)
{
    string text = tbAssembly.Text;
    string dirname = Path.GetDirectoryName(text);

    if (Directory.Exists(Path.GetDirectoryName(dirname)))
    {
        string[] files = Directory.GetFiles(dirname, "*.*", SearchOption.TopDirectoryOnly);
        string[] dirs = Directory.GetDirectories(dirname, "*.*", SearchOption.TopDirectoryOnly);
        var candidates = new List<string>();

        Array.ForEach(new String[][] { files, dirs }, (x) =>
            Array.ForEach(x, (y) =>
                      {
                          if (y.StartsWith(dirname, StringComparison.CurrentCultureIgnoreCase))
                              candidates.Add(y);
                      }));

        tbAssembly.ItemsSource = candidates;
        tbAssembly.PopulateComplete();
    }
}

It works, just the way you’d expect. It feels professional. There are none of the anomalies that the codeproject control exhibits. This is what it looks like: