Change background brush in trigger does not work

[Maxima078]

Description

When current background brush is a LinearGradientBrush, a trigger cannot update background to SolidColorBrush. Using a setter to update BackgroundColor does not work either.

Steps to Reproduce

• Set a frame background to a LinearGradientBrush
• Add a trigger with a setter updating background to a SolidColorBrush
• Make your trigger trigger

Actual Behavior

Background is not updated

Expected Behavior

Background is updated

Basic Information

• Version with issue: Xamarin.Forms 5.0.01874
• Last known good version: none (tested with 4.8.x.x)
• Platform Target Frameworks:
  • Android: 10
• Affected Devices: Physical devices

Workaround

Use a LinearGradientBrush with two GradientStop set to the expected solid color

[jsuarezruiz]

@Maxima078 On what platform/s does it happen? Could you attach a small example where to reproduce the issue?
I did a quick test, but cannot reproduce the issue:

[Maxima078]

I have reproduced it on Android 10 with a physical device. Here is a repro:
Sample1.zip

[Maxima078]

I've just tried with a simulator (Pixel 2 Android 9) and got the same result:

[Karmageddonium]

Found some workaround:
It seems like u can replace brush with only same type brush (gradient -> gradient) with the same(!) count of gradientStops.
So id u would like to replace this

with this

you should do like this:

IMPORTANT

In the head of the issue there is a text "May be fixed by #13438"
that way offers to set background to {x:Null} before changing gradientBrush to solidColor - it works BUT it can cause further problems with background (for example CornerRadius breaks down)