RichTextBlock text line count

Question

I am working on Windows Phone 8.1 application and I got this issue:

I have a RichTextBlock control which holds my text, if my control height is bigger than my screen I need to scroll line by line automaticly while the user reads the text.

Is there any way to determine the number of the lines in my RichTextBlock or geometric calculation is the only way?

I've tried to iterate over the Blocks collection, but nothing seems to be relevant.

The only thing that I've came with is by using TextPointer.GetCharacterRect function:

if(msgContainer.Blocks.Any())
{
    var item = msgContainer.Blocks.FirstOrDefault();

    var height = item.LineHeight;
    var startRect = item.ContentStart.GetCharacterRect(LogicalDirection.Forward);

    var lineHeight = startRect.Height;
    var lineCount = (int)_fatAssTextMessage.ActualHeight / lineHeight;
}

But it isn't accurate - sometimes it misses by line or two since the int casting, and the division...

Any help will be appreciated

Well, there is not property Lines in my control: Windows.UI.Xaml.Controls.RichTextBlock — Pavel Durov, Dec 22 '15 at 09:34
Then count for `'\r'` and `'\n'` in whole text. They are equal to ENTER key or newline. — sharp, Dec 22 '15 at 09:37
@FiN text boxes can wrap, using newline delimiters will not always work. — Barnstokkr, Dec 22 '15 at 09:42

score 1 · Accepted Answer · answered Dec 22 '15 at 10:09

You'll get a slightly more accurate count if you do the cast after you've done the division:

var lineCount = (int)(_fatAssTextMessage.ActualHeight / lineHeight);

Currently you are casting the actual height to an integer and then doing the division which will always undercount the number of lines.

This will also undercount occasionally - when you have half a line visible. To ensure you always get the largest possible value do something like this:

var lineCount = (int)Math.Ceiling(_fatAssTextMessage.ActualHeight / lineHeight);

[Math.Ceiling] Returns the smallest integral value that is greater than or equal to the specified double-precision floating-point number.

Source

Yes, it really gets me a better results. I still believe that there suppose to be a better way to deal with this functionality. — Pavel Durov, Dec 22 '15 at 10:27

RichTextBlock text line count

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