c# - How to delete the file of a PrivateFontCollection.AddFontFile?

Question

We create a large count of fonts for a short use. The fonts are embedded in documents. I want delete the font files if not use anymore. How can we do this? The follow simplified code does not work:

PrivateFontCollection pfc = new PrivateFontCollection();
pfc.AddFontFile(fontFile);
FontFamily family = pfc.Families[0];
Console.WriteLine(family.GetName(0));

family.Dispose();
pfc.Dispose();
GC.Collect();
GC.WaitForPendingFinalizers();
File.Delete(fontFile);

The delete of the file is failing because the file is locked. What can I do else to free the file lock?

PS: Before we have use AddMemoryFont. This work with Windows 7. But with Windows 8 .NET use the wrong font files after the first FontFamily was Disposed. Because every Document can contain other fonts we need a very large count of fonts and can not hold references to all.

Answer 1

After looking in the code of method AddFontFile:

public void AddFontFile(string filename)
{
    IntSecurity.DemandReadFileIO(filename);
    int num = SafeNativeMethods.Gdip.GdipPrivateAddFontFile(new HandleRef(this, this.nativeFontCollection), filename);
    if (num != 0)
    {
        throw SafeNativeMethods.Gdip.StatusException(num);
    }
    SafeNativeMethods.AddFontFile(filename);
}

we see that the font is registered 2 times. First in GDI+ and in the last line in GDI32. This is different to the method AddMemoryFont. In the Dispose method it is only unregistered in GDI+. This result in a leak in GDI32.

To compensate this you can call the follow:

[DllImport("gdi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
public static extern int RemoveFontResourceEx(string lpszFilename, int fl, IntPtr pdv);

pfc.AddFontFile(fontFile);
RemoveFontResourceEx(fontFile, 16, IntPtr.Zero);