I have another problem: The IsTextTrimmed property is recalculated if the textblock size is changed (e.g. if the UI is resized). However, it doesn’t get recalculated if the textblock’s content is changed. I’m using binding to set the textblock’s value, and IsTextTrimmed is calculated correctly when the field is displayed initially. However if the underlying Text value is then changed to something else, IsTextTrimmed doesn’t get recalculated (unless you jiggle the edge of the UI!)

It seems that where we register the handler for the SizeChangedEvent, we also need to do something similar for when the Text property’s value is changed.
I’ve tried various things but haven’t found an elegant solution. Any ideas?

Thank You!!!! Handling wrapped TextBlocks was the final missing piece, it works perfectly now!

// If there is only a word
if (!string.IsNullOrEmpty(formattedText.Text) &&
!formattedText.Text.Contains(” “))
{
return (int)formattedText.Width >
(int)textBlock.ActualWidth);
}

I had a hunch that algorithm wouldn’t work for multi-line text boxes and if I remember correctly, is partly why I added the condition on TextWrapping (though it’s been a while, now).

Glad you got it working; I’m updating the code sample to reflect the more inclusive algorithm. It now works with multi-line TextBlocks and with TextWrapping enabled or disabled.

Replace the last return statement in CalculateIsTextTrimmed by:

formattedText.MaxTextWidth = textBlock.ActualWidth;

return (formattedText.Height > textBlock.ActualHeight);

So, the FormattedText instance is given a max width, so if it has to occupy more height than the given TextBlock, it means that the text was trimmed.
This also works for a single-line text block.