[Proposal] Expander animation

[stephenquan]

Feature name

Expander update to support animation with new animation properties:

• bool AnimationsEnabled { get; set; } // default: true;
• Easing? CollapseEasing { get; set; } // default: null;
• unit CollapsingDuration { get; set; } // default: 250u;
• Easing? ExpandEasing { get; set; } // default: null;
• unit ExpandDuration { get; set; } // default: 250u;

Link to discussion

https://github.com/CommunityToolkit/Maui/discussions/1628

Progress tracker

• [x] Android Implementation
• [x] iOS Implementation
• [x] MacCatalyst Implementation
• [x] Windows Implementation
• [ ] Tizen Implementation
• [ ] Unit Tests
• [x] Samples
• [ ] Documentation (TODO: document the 5 new properties)

Summary

This issue and the corresponding PR is to continue a conversation that started in the discussion forums on how we may introduce animations to the Expander component.

Motivation

The Expander component could be improved to support animation.

Detailed Design

[5th April 2025, Refactor/Rewrite]

We will achieve animation by putting the Content inside of a VerticalStackLayout and we will animate the VerticalStackLayout.Height. The pseudo-code of how this may work is:

<!-- Expander pseudo-code implementation: -->
<Grid RowDefinitions="Auto,Auto">
    <ContentView Content="{Binding Header}"/>
    <!-- Animations on VerticalStackLayout.Height from 1 (Collapsed) to Content.Height+1 (Expanded) -->
    <VerticalStackLayout Padding="0,1,0,0" HeightRequest="1">
       <ContentView Content="{Binding Content}"/>
    </VerticalStackLayout>
</Grid>

Drawbacks

There are several issues encountered:

• When collapsed, I couldn't set VerticalStackLayout.Height = 0 because, if I did, I couldn't calculate the height of the user's Content (it's why the VerticalStackLayout.Height starts at 1)
• One of the samples Expander with GridItemLayout doesn't consistently work

Unresolved Questions

No response

[crwsolutions]

bool AnimationEnabled (default true)

+1

Setting default to false is also fine for me (it might provide a better upgrade path), but I would prefer to simply have a switch that just works.

[stephenquan]

From reading the above comments from @crwsolutions as well as https://github.com/CommunityToolkit/Maui/pull/2522#issuecomment-2762733760 there seems to be support for one of the solutions that I depicted in the "Alternatives". When there is free time, I will move the current implementation into a branch so that the main branch can be repurposed for this alternate solution.