How to highlight the word(s) with bold in text block for specified keyword using the attached property

Question

The objective is to bold the word(s) of text in Textblock with matching input keyword.

For example: Stackoverflow is a very helpful, keep using Stackoverflow to sharpen

Answer 1

Whether you want to modify a TextBlock FontWeight attribute or another display property, I've written the following static method and found it very useful. (Note: The method illustrates highlighting text by modifying the Foreground property. The same principle can be used for any other TextBlock display attribute.)

    static Brush DefaultHighlight = new SolidColorBrush(Colors.Red);

    public static void SetTextAndHighlightSubstring(this TextBlock targetTextBlock, string sourceText, string subString, Brush highlight = null)
    {
        if (targetTextBlock == null || String.IsNullOrEmpty(sourceText) || String.IsNullOrEmpty(subString))
            return;
        targetTextBlock.Text = "";
        var subStringPosition = sourceText.ToUpper().IndexOf(subString);
        if (subStringPosition == -1)
        {
            targetTextBlock.Inlines.Add(new Run { Text = sourceText });
            return;
        }
        var subStringLength = subString.Length;
        var header = sourceText.Substring(0, subStringPosition);
        subString = sourceText.Substring(subStringPosition, subStringLength);
        var trailerLength = sourceText.Length - (subStringPosition + subStringLength);
        var trailer = sourceText.Substring(subStringPosition + subStringLength, trailerLength);
        targetTextBlock.Inlines.Add(new Run { Text = header });
        targetTextBlock.Inlines.Add(new Run { Text = subString, Foreground = highlight ?? DefaultHighlight });
        targetTextBlock.Inlines.Add(new Run { Text = trailer });
    }

You can call this method using the TextBlock extension syntax like so:

TextBlockTitle.SetTextAndHighlightSubstring(_categoryItem.ItemText, _searchText);

In this example, the following display resulted: