Replacement for missing TextTrimming option "CharacterEllipsis" in Silverlight

Question

Silverlight (at least, as of Version 4) has no CharacterEllipsis option for TextTrimming, which WPF has. It could be used on a TextBlock. That means, If there is not enough room to display "That's incredible", I could trim to "That's..." but not to "That's incred..." which we'd rather want.

I though, we'd try to implement our custom text trimming function. Basically, thats not that hard. A quite stupid way is to measure the pixels for a string, compare to the available width and manipulate the string by cutting last character and adding "..." in a loop while the text still doesn't fit. Here is an example how this could work:

// Not perfect but good enough for us
private bool AutoTrim(string fullText, TextBlock textBlock, double maxWidth)
{
    double factor = maxWidth / textBlock.ActualWidth;
    if (factor > 1)
        return false;

    int newTextLength = (int)Math.Floor((double)fullText.Length * factor);
    string trimTest;
    do
    {
        trimTest = fullText.Substring(0, newTextLength--);
        textBlock.Text = trimTest + "..."; // problematic...
        factor = maxWidth / textBlock.ActualWidth;
    }
    while (factor < 1 && newTextLength > 0);

    return true;
}

But doing that in code behind (or within a Behavior) leads to some problems: For example, when we want to update the displayed text and set the TextBlock's TextBlock1.Text = ... Property, it actually might change our viewModel if the Text is bound to a ViewModel Property. Another problems occur as we noticed that view and viewModel might run of of sync for some reason (we noticed that in a ListBox).

Do you have a better idea on how to solve this problem in a good way?

Answer 1

Robby Ingebretsen's DynamicTextBox does this by wrapping the TextBlock in a custom control and measuring the available size. It matches the CharacterEllipsis text trimming mode of WPF. WordEllipsis mode did get added to Windows Phone 7 Mango, but that isn't much help here.

Answer 2

Dan Wahlin used a converter before TextTrimming="WordEllipsis" was added to Silverlight 4. You can find it here: http://weblogs.asp.net/dwahlin/archive/2010/05/05/text-trimming-in-silverlight-4.aspx