Remove Non-Tokenized Text in RadAutoCompleteBox

Updated on Jan 8, 2026

Environment

Product Version	Product	Author
2025.4.1111	RadAutoCompleteBox for WinForms	Dinko Krastev

Description

The control allows you to disable suggesting already selected item in the drop-down list. However, the duplicate entries become text instead of tokens. In this article we will demonstrate how to not let non-tokenized text remain after losing focus.

Solution

Customizing RadAutoCompleteBox Behavior

To prevent non-tokenized text from appearing, override the InsertTokenizedTextBlocks() method inside the AutoCompleteBoxViewElement class. Replace the RadAutoCompleteBox control with a custom class, as shown below:

C#

public class MyAutoCompleteBoxControl : RadAutoCompleteBox
{
    public override string ThemeClassName => typeof(RadAutoCompleteBox).FullName;

    protected override RadTextBoxControlElement CreateTextBoxElement()
    {
        return new MyAutoCompleteBoxElement();
    }
}

public class MyAutoCompleteBoxElement : RadAutoCompleteBoxElement
{
    protected override Type ThemeEffectiveType => typeof(RadAutoCompleteBoxElement);

    protected override TextBoxViewElement CreateViewElement()
    {
        return new MyAutoCompleteBoxViewElement();
    }
}

public class MyAutoCompleteBoxViewElement : AutoCompleteBoxViewElement
{
    protected override Type ThemeEffectiveType => typeof(AutoCompleteBoxViewElement);

    protected override int InsertTokenizedTextBlocks(int index, string text, bool performInvalidation)
    {
        StringBuilder stringBuilder = new StringBuilder();
        foreach (char c in text)
        {
            if (c == this.Delimiter)
            {
                if (stringBuilder.Length > 0)
                {
                    string text2 = stringBuilder.ToString();
                    if (!performInvalidation || OnTokenValidating(text2))
                    {
                        ITextBlock textBlock = CreateBlock(text2, TokenizedTextBlockElementType);
                        textBlock.Index = index;
                        Children.Insert(index, textBlock as RadElement);
                    }
                    index++;
                    stringBuilder = new StringBuilder();
                }
            }
            else
            {
                stringBuilder.Append(c);
            }
        }

        if (stringBuilder.Length > 0)
        {
            index = base.InsertTextBlocks(index, stringBuilder.ToString(), TextBoxWrapPanel.TextBlockElementType) + 1;
        }

        return index - 1;
    }
}

Handling Focus Loss

To validate tokens when the control loses focus, subscribe to the LostFocus event and insert the delimiter symbol manually:

C#

this.radAutoCompleteBox1.LostFocus += RadAutoCompleteBox1_LostFocus;

private void RadAutoCompleteBox1_LostFocus(object sender, EventArgs e)
{
    ITextBoxNavigator navigator = (this.radAutoCompleteBox1.TextBoxElement as MyAutoCompleteBoxElement).Navigator;
    TextPosition startPosition = navigator.SelectionStart ?? TextPosition.GetFirstPosition(this.radAutoCompleteBox1.TextBoxElement.ViewElement);
    TextPosition endPosition = navigator.SelectionEnd ?? startPosition;
    this.radAutoCompleteBox1.TextBoxElement.ViewElement.Insert(endPosition, ";");
}