Introduce ButtonStyle equivalent customisation for Slider and RangeSlider

[TahaTesser]

Is there an existing issue for this?

• I have searched the existing issues
• I have read the guide to filing a bug

Use case

Customizing Slider and RangeSlider should be as easy as customizing buttons. Currently customizing Slider and RangeSlider is complex and messy.

Right now just to customize the border radius of the slider components such as track or value indicator you need to copy the source code for that component and modify its radius. We don't do this for any other widget.

Some slider components have radius customization but others don't. it'd be better to have consistent customization as we have for different material buttons.

flutter/packages/flutter/lib/src/material/slider_theme.dart

Lines 282 to 290 in ce32282

	this.overlayShape,
	this.tickMarkShape,
	this.thumbShape,
	this.trackShape,
	this.valueIndicatorShape,
	this.rangeTickMarkShape,
	this.rangeThumbShape,
	this.rangeTrackShape,
	this.rangeValueIndicatorShape,

There are separate active, inactive, and disabled colors to be provided. These should be using material states.

flutter/packages/flutter/lib/src/material/slider_theme.dart

Lines 267 to 276 in ce32282

	this.activeTrackColor,
	this.inactiveTrackColor,
	this.secondaryActiveTrackColor,
	this.disabledActiveTrackColor,
	this.disabledInactiveTrackColor,
	this.disabledSecondaryActiveTrackColor,
	this.activeTickMarkColor,
	this.inactiveTickMarkColor,
	this.disabledActiveTickMarkColor,
	this.disabledInactiveTickMarkColor,

slider_theme.dart:

1. A lot of component code is repeated with only slight variation.
2. Default component values are hard coded and not available in a single config class.
3. Many components aren't customizable and require copying the source code for minor and major customizable.

Proposal

• Introduce a ButtonStyle equivalent customization class for Slider and RangeSlider
• Add something similar to ButtonStyle.from when you want to just customize default components such as radius, size, elevation, etc.
• Regular style class to take entire custom shape components like the current SliderThemeData.
• Add material state support track color, mark color, and value indicator color.
• Make it as simple as possible to customize any default components of Slider and RangeSlider while keeping the ability to provide your own custom shapes.

I will implement this as part of #125329

[TahaTesser]

cc: @HansMuller @Piinks
Any feedback would be appreciated.

[Piinks]

Would this mean eventually deprecating and removing the properties above?
I think this is a good idea, @HansMuller and @guidezpl may have some material specific thoughts though. :)

[HansMuller]

I think this is a nice idea. It will require some careful planning. A design doc would be helpful.

I agree with @Piinks about deprecating old redundant API however I don't think we want to introduce changes that cannot be flutter fixed (i.e. that can't be migrated automatically), even if that means leaving some of the old API behind. In that sense this would be unlike the migration to the ButtonStyle et al. API.

[guidezpl]

I think this is a nice idea. It will require some careful planning. A design doc would be helpful.

I agree with @Piinks about deprecating old redundant API however I don't think we want to introduce changes that cannot be flutter fixed (i.e. that can't be migrated automatically), even if that means leaving some of the old API behind. In that sense this would be unlike the migration to the ButtonStyle et al. API.

+1

[TahaTesser]

I think this is a nice idea. It will require some careful planning. A design doc would be helpful.

Thank you! I'm definitely going to create a design doc.