How to get the current theme variant?

[drognisep]

I'm not sure how to get the current theme variant to look up a color. I'm trying to set the color of a background canvas rectangle in a stack container, since the foreground content has a transparent background and I don't want to see the content behind the stack container. The theme API for querying colors requires a variant. I'm not overriding the theme in any way, so I want to just get the current variant. What is the correct/intended method to get the current theme variant?

// Theme defines the method to look up colors, sizes and fonts that make up a Fyne theme.
//
// Since: 2.0
type Theme interface {
	Color(ThemeColorName, ThemeVariant) color.Color // What I'm trying to use
	Font(TextStyle) Resource
	Icon(ThemeIconName) Resource
	Size(ThemeSizeName) float32
}

What I'm doing now doesn't seem right. It looks like there are light and dark constants for this value, but not a "Current."

// What I'm doing right now
respBG := canvas.NewRectangle(theme.Current().Color(theme.ColorNameBackground, 0 /* maybe isn't used? */))

The builtin theme seems to potentially disregard this parameter anyway, so I'm not sure what to use to reference the current theme.

// theme.go

// Existing constants

// Keep in mind to add new constants to the tests at test/theme.go.
const (
	// VariantDark is the version of a theme that satisfies a user preference for a dark look.
	//
	// Since: 2.0
	VariantDark = internaltheme.VariantDark

	// VariantLight is the version of a theme that satisfies a user preference for a light look.
	//
	// Since: 2.0
	VariantLight = internaltheme.VariantLight
)

/* ... */

// Color implementation of the builtinTheme, where it looks like the parameter is overridden.

func (t *builtinTheme) Color(n fyne.ThemeColorName, v fyne.ThemeVariant) color.Color {
	if t.variant != internaltheme.VariantNameUserPreference {
		v = t.variant
	}

/* ... */

[dweymouth]

It's fyne.CurrentApp().Settings().ThemeVariant() IIRC. Perhaps adding a theme.CurrentVariant() as an alias would be a worthwhile feature request

[drognisep]

That seems to work. Thanks! :)

[andydotxyz]

I think you might have been asking the wrong question.
If you want to look up a colour for the current theme and variant then use theme.Color(fyne.ThemeColorName).

[dweymouth]

Adding onto this, if you want to look up a color for writing a custom widget, use theme.ColorForWidget(theme.ColorNameWhatever, myWidget)

[drognisep]

Oh! That makes sense. I assumed I would need to reference the theme first to contextualize the call, but that's even easier.

Thanks @andydotxyz! :)

[andydotxyz]

One additional item to consider is that the app theme is not necessarily what applies to a single widget. Since 2.6 we have a ThemeOverride container that groups items in a separate themed area. So getting the app theme will return the wrong theme if your widget is currently inside one of those containers.

The theme.ColorForWidget and more generally theme.CurrentForWidget will tell you what theme applies to a widget that is being overridden in this way.

[drognisep]

Ah, I think I'm following. So, is the intent that the user always sets the variant (or it defaults from the system), but the theme is variable because it can be overridden by the developer either globally or at the widget level?

[andydotxyz]

Hmm, they are both variable but in different ways. As you say the developer sets the theme or overrides it for areas, but the variant can also change at any time due to system activity like light-dark switching at dusk (macOS, iOS)...

[drognisep]

That makes sense. I imagine that the user could also opt to toggle the variant if the developer provides a means to do that, which is one case where listeners come in for foundational canvas elements to update themselves.

If the variant is then overridden in a custom theme with a static value in Color, then we couldn't figure out what variant is being used from the outside looking in, but the override will correct anyway. Does that sound right? I'm thinking about the pattern you applied in this video to ensure that the light variant is always used.

[andydotxyz]

If the variant is then overridden in a custom theme with a static value in Color, then we couldn't figure out what variant is being used from the outside looking in, but the override will correct anyway

Any theme can ignore the variant if it decides

[drognisep]

Nice! Thanks for clarifying. I think this will help a lot with the theme docs. :)