Proposal: Add some animations to Expander

[ShankarBUS]

Summary

This proposal is to add some animations to the Expander control as in WCT

Rationale

The only parts this library missing from WinUI are the nice little animations in it.
While animating other controls might be hard, animating the Expander control is relatively easy.
I know this due to limitation in WPF and this is how it works. "But it is not impossible."

See this codeproject article : Customizing WPF Expander with ControlTemplate by XiaoChuan Yu. A basic implementation like this would be appreciated

Screenshots

Expander from WCT

Expander from this library

Additional Context

I may be a little biased since I need this for one of my apps. But no would say they don't need fluid animations.
Implementing this will be a nice addition to this library.
If you are okay I will work on this and submit a PR for this

[Kinnara]

Good idea. Is there a "standard" expand/collapse animation in UWP/WinUI that we can borrow, to make our animation as native as possible?

[ShankarBUS]

There is no expander in WinUI AFAIK, it's from the Windows Community Toolkit (aka WCT), the presets could be there.

[ShankarBUS]

I have some questions :

• Should the header be rotated when in Left/Right Expand mode?
• Should we match the the UI from WCT? Or keep the current and just add animations? (IMO the UI in this lib is far better than the one in WCT)
• They don't have separate styles for each direction, they have a single template for all directions. Any ideas?
• In their Implementation the arrow always points towards the header content and will turn clockwise and perpendicular to the header content, In your implementation the arrow will point towards expand direction and turns 180 degrees when expanded (I personally like your implementation), Any ideas?

[ShankarBUS]

Hey @Kinnara,
Are you planning on implementing this, should I open a PR? Are you gonna implement it yourself?
I have done half of the job in commit 8aaee4b in my fork, am I allowed to open a PR?

[Kinnara]

If this proposal is accepted, we can port the control (or just the animations) over.

[ShankarBUS]

That's why I closed the related PR.

I don't have a solid decision on whether to port the whole API or just the animations.

Since most of the apps already use the WPF expander, creating a custom style would be a good option. But that shouldn't stop innovation.

IMO, We must go with porting the whole control.

[ShankarBUS]

@Kinnara, the proposal was accepted, a PR was made and got mergerd 🎉🥳

microsoft/microsoft-ui-xaml@ce84da3

What about now?

[Kinnara]

We probably want to first update the styling of the WPF Expander to match the WinUI one. I'll need to take a closer look to see what's possible and what's not.