[Span] Improve formatting inheritance

[pjcollins]

Fixes: #21034

Label has been updated to set corresponding formatting properties on
its Span children if they are set.

One behavior to mention with respect to iOS is that font attributes can
not be forced on font families that do not support them. The .NET 8
templates use OpenSansRegular as a font family for Labels by default,
and with these changes child spans will now inherit this font family as
well. More context for this behavior is described in issue #1018.

There is some discussion related to Style inheritance in issue #21034,
however this appears to be a more complex issue. Span does not inherit
from Label directly, and as such a style with a target type of Label
can not currently be applied to a Span. This will potentially require
follow up investigation in a separate issue/PR.

[StephaneDelcroix]

If I recall correctly, if a format property isn't set on the Span, it will use the format property of the label

I believe this isn't the right fix for the reported issue

[pjcollins]

If I recall correctly, if a format property isn't set on the Span, it will use the format property of the label

I believe this isn't the right fix for the reported issue

This does appear to be the case for some formatting properties, but there is inconsistency between platforms.

If we compare Android FormattedStringExtensions with iOS FormattedStringExtensions, iOS is missing TextDecorations info from its label, while Android is missing LineHeight when compared to iOS. BackgroundColor is missing from both. The Windows and Tizen cases appear to have similar issues.

In my first look at this I was attempting to address issues at the platform level, and can revisit that if that seems like the more appropriate fix? Assigning values when setting up the Spans felt like a more comprehensive and more easily tested fix though (assuming full inheritance when unset is the behavior we want).

I may also be missing somewhere else where Span gets formatting information from its associated Label?

[PureWeen]

If I recall correctly, if a format property isn't set on the Span, it will use the format property of the label
I believe this isn't the right fix for the reported issue

This does appear to be the case for some formatting properties, but there is inconsistency between platforms.

If we compare Android FormattedStringExtensions with iOS FormattedStringExtensions, iOS is missing TextDecorations info from its label, while Android is missing LineHeight when compared to iOS. BackgroundColor is missing from both. The Windows and Tizen cases appear to have similar issues.

In my first look at this I was attempting to address issues at the platform level, and can revisit that if that seems like the more appropriate fix? Assigning values when setting up the Spans felt like a more comprehensive and more easily tested fix though (assuming full inheritance when unset is the behavior we want).

I may also be missing somewhere else where Span gets formatting information from its associated Label?

Maybe we could add some explicit interfaces to span itself for ITextElement?
https://github.com/dotnet/maui/blob/d7dac41200a932ea748569a28b6f26e7e3df69db/src/Controls/src/Core/Span.cs#L10C2-L10C122

And then if "textcolor" isn't set it returns the "textcolor" from the label. We usually use the interfaces to simplify interaction from the platform level and then use the implementation of it to calculate what the platform needs to know.

[rmarinho]

Hey just saw this .. seems ifs set a TextColor on my Label, my spans don t respect.

[jsuarezruiz]

Hey just saw this .. seems ifs set a TextColor on my Label, my spans don t respect.

@pjcollins