How to dispose FormattedText / make WPF let go of .TTF file?

Question

In my WPF application I have a custom Canvas implementation, in which I draw some text using a specified .ttf file. The ttf file resides in a temporary location that can be deleted at some later point in time. My problem is that once my text has been rendered on the canvas, the ttf file seems to be kept open, and can't be deleted until the application has been closed down. Is seems to be the FormattedText instance that keeps the font file open. Does anybody know a way to "Dispose" the FormattedText, or in any other way make sure that the font file is closed after rendering?

My text drawing code:

public class MyCanvas : System.Windows.Controls.Canvas
{
    protected override void OnRender(DrawingContext dc)
    {
        base.OnRender(dc);

        // Some other drawing stuff...

        FontFamily fontFamily = new FontFamily(fontUri);
        Typeface typeFace = new Typeface(fontFamily, FontStyles.Normal, FontWeights.Normal, FontStretches.Normal);
        FormattedText formattedText = new FormattedText(chars, System.Globalization.CultureInfo.InvariantCulture, FlowDirection.LeftToRight, typeFace, text.FontHeight, new SolidColorBrush(color));
        dc.DrawText(formattedText, new Point(text.X + offsetX, text.Y + offsetY));
        int textWidth = (int) formattedText.Width;
        int textHeight = (int)formattedText.Height;

        // Drawing continues...
    }
}

Note: It seems I don't even have to call DrawText to lock the font file (tried commenting that line out). Using the formattedText instance to assign the textWidth and textHeight variables is enough for WPF to keep the file open.

Update: I've not been able to solve this problem, so currently I'm using a workaround that creates a new temporary font directory if overwriting the existing one fails. It works, but I'm not very happy with having to do it like this, so I'm still interested in any suggestions how to fix this.

Answer 1

Perhaps it's related in some way to the Presentation Font Cache, a service that runs to cache font data structures so that WPF apps perform better....maybe it is keeping the file locked.

Try to change the Presentation Font Cache service so that it is Stopped and Disabled. Run your application, then try and see if you can delete the font file.

Disabling the Presentation Font Cache isn't a long term solution if it is in fact the cause. You might get away with programmatically stopping and restarting it...not sure how that would affect other running WPF applications.

There is a more definitive way to see who has the file locked, by using a tool e.g.

• http://windowsxp.mvps.org/processlock.htm

A possible solution (to get around whoever is locking the file) is to put the .TTF file as a Resource in your application, then you can let WPF worry about how to manage and clean it up.

Links:

• http://msdn.microsoft.com/en-us/library/ms753303.aspx

• WPF PresentationFontCache. What is this?

• http://blog.tune-up.com/myth-buster/the-case-of-the-mysterious-presentation-font-cache-cpu-hog/

UPDATE:

You could create a wrapper class whose job is to delete a file when the object is disposed or if it can't delete the file at dispose time because the file is still locked, then it will get deleted when the Garbage Collector calls the Finalizer.

• http://www.codeproject.com/Articles/84831/A-simple-technique-to-take-care-of-temporary-files

Another possiblity is to use FileOptions.DeleteOnClose - you'd have to see if it was possible to use FontFamily on a font file that you opened/created and are currently maintaining an open file handle on.

• FileStream with DeleteOnClose File option

You say "The ttf file resides in a temporary location that can be deleted at some later point in time."...when you say at some later point in time...I'm presuming it's when you exit the program/process....or is that not the case?

or try TempFileCollection:

• http://msdn.microsoft.com/en-us/library/system.codedom.compiler.tempfilecollection.aspx