Setting FontFamily at runtime (custom font)?

[kuiperzone]

First of all, I want to say thank you to Avalonia for producing the following for packaging custom fonts:

https://docs.avaloniaui.net/docs/guides/styles-and-resources/how-to-use-fonts

It always been a confusing topic and error prone, so its incredibly helpful, however, I still I have no real idea how to set TextBlock.Font family at runtime. In the past, I have spent days pouring over this issue, and sometimes it works, and then it doesn't. I primarily want to do this at runtime, and all the examples seem to be XAML.

Please have patience with me on this.

So lets suppose I wish to use a custom font I've packaged as a resource, so I include the following the csproj:

<ItemGroup>
    <AvaloniaResource Include="Assets\**" />
</ItemGroup>

Then in the App.axaml:

<Application.Resources>
    <FontFamily x:Key="NunitoFont">avares://GoogleFonts/Assets/Fonts#Nunito</FontFamily>
</Application.Resources>

So what should FontFamily be at runtime?

TextBlock.FontFamily = "NunitoFont" ?
TextBlock.FontFamily = "#NunitoFont" ?

Or something else?

PS.

How is FontFamily handled if I do something like:

TextBlock.FontFamily = "serif"
TextBlock.FontFamily = "monospace"

This doesn't seem to do anything, so I'm guessing if falls to "Inter".

What happens if I set just:

TextBlock.FontFamily = "Inter" ?

Does it find "Inter", or does it not find it, but then falls back to Inter?

This is relevant where the Family needs to be set from a drop down box at the UI.

Thank you

[stevemonaco]

So what should FontFamily be at runtime?

TextBlock.FontFamily = new FontFamily(@"avares://AvaloniaApplication/Assets/Fonts#Nunito"); // For a resource-based font
TextBlock.FontFamily = new FontFamily("Times New Roman"); // For a system font

I tend to store these in a static class instead. eg.

public static class AppResources
{
    public static FontFamily Nunito { get; } = new FontFamily(@"avares://AvaloniaApplication/Assets/Fonts#Nunito");
}

However, I'm not able to create+add an EmbeddedFontCollection and simply do new FontFamily("Nunito"). I think this is because the following code does only considers System fonts instead of looping all of its _fontCollections. The FontFamily key is null in my testing:

Avalonia/src/Avalonia.Base/Media/FontManager.cs

Lines 130 to 138 in aabd038

	else
	{
	var familyName = fontFamily.FamilyNames.PrimaryFamilyName;
	if (SystemFonts.TryGetGlyphTypeface(familyName, typeface.Style, typeface.Weight, typeface.Stretch, out glyphTypeface))
	{
	return true;
	}
	}

So I can't get something like this to work:

var fc = new EmbeddedFontCollection(new Uri("fonts:App", UriKind.Absolute), new Uri(@"avares://AvaloniaApplication/Assets", UriKind.Absolute));
FontManager.Current.AddFontCollection(fc);

text.FontFamily = new FontFamily("Nunito");

When I try using FontManager.Current.TryGetGlyphTypeface, I receive "Segoe UI" on Win11, so I guess a default system font:

var ff = new FontFamily(new Uri("fonts:App"), "Nunito");
var tf = new Typeface(ff);
FontManager.Current.TryGetGlyphTypeface(tf, out var gtf);

That's about as far as I can troubleshoot for now. (Actual testing was done with Anton SC as Nunito looks too similar to Inter)

[stevemonaco]

No, not necessary to put into resources if you always specify the full asset uri with new FontFamily(...).

I prefer static classes for "resources" that are never swapped or need to be overridden lower in the visual tree. Less resource keys, compile-time errors instead of runtime errors, and it's easy to consume from both XAML ({x:Static ...}) and code.

[Gillibald]

If you define a font family without a source we implicitly map the name to the system font collection.

https://github.com/AvaloniaUI/Avalonia/blob/master/src/Avalonia.Base/Media/FontManager.cs#L21

So FontFamily="Segoe UI" becomes FontFamily="fonts:SystemFonts#Segoe UI"

[kuiperzone]

Thank you.

What does the prefix "fonts:" do? As in FontFamily="fonts:...?

If I put some kind of resource in my App.Axaml, can I use FontFamily="fonts:MyFonts#Nunito?

[stevemonaco]

Ah, good to know. Thanks!

For anybody following along, this is possible today (fixing my example above):

var fc = new EmbeddedFontCollection(new Uri("fonts:App", UriKind.Absolute), new Uri(@"avares://AvaloniaApplication25/Assets", UriKind.Absolute));
FontManager.Current.AddFontCollection(fc);

text.FontFamily = new FontFamily("fonts:App#Nunito");

It leaks a bit of font storage knowledge vs simply "Nunito", so I do wish any added FontCollections would be searched before the default font is used, but I might be bikeshedding.

I still prefer the static class approach if your entire set of custom fonts is known at compile-time and come from resources.

[kuiperzone]

Thank you @stevemonaco . Your answer really helped!