WrapPanel inside Listbox (ItemsPanelTemplate) only work/wrap with FluentTheme.

[H97-Git]

Describe the bug

1. WrapPanel inside a ListBox doesn't wrap.
2. If used with anything else than FluentTheme.

To Reproduce

Quick repo to reproduce

Avalonia.Sandbox

Expected behavior

WrapPanel should wrap regardless of the theme used.

Avalonia version

11.0.10

OS

Windows

Additional context

I was testing ActiPro theme/Controls inside my app and using the theme broke the layout for my file explorer.
At first I thought it was an ActiPro issue but with further testing I saw that WrapPanel inside ListBox only wrap with FluentTheme.

Maybe I did something wrong and this is not a bug but I will rather ask.

[MrJul]

It isn't really related to WrapPanel itself.

The HorizontalScrollBarVisibility for ListBox is set to Auto in the Simple theme:

Avalonia/src/Avalonia.Themes.Simple/Controls/ListBox.xaml

Line 10 in b30894c

<Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto" />

This gives the control infinite horizontal space, so as far as the WrapPanel is concerned, there's enough space and nothing is wrapped. The default is Disabled, which is what the Fluent theme uses.

Add ScrollViewer.HorizontalScrollBarVisibility="Disabled" to your ListBox and it'll work with all themes.

That being said, I'm leaving this issue open, as I'm not sure sure why the Simple theme uses Auto here. Git blame says that it was Auto for both themes in the past, then Fluent was changed to Disabled, but Simple hasn't been touched.

I suggest we change the default to Disabled for the Simple theme too.

[H97-Git]

Oh! I see, that does make sense. 😄

I'm not sure how to:

Add ScrollViewer.HorizontalScrollBarVisibility="Disabled" to your ListBox and it'll work with all themes.

But following #12029, I did:
ScrollViewer.SetHorizontalScrollBarVisibility(SandBoxListBox,ScrollBarVisibility.Disabled);

And it solved my issue. ❤️
Thank you!

[MrJul]

I'm not sure how to:

Add ScrollViewer.HorizontalScrollBarVisibility="Disabled" to your ListBox and it'll work with all themes.

As typed :) It's an attached property, like Grid.Row:
<ListBox ScrollViewer.HorizontalScrollBarVisibility="Disabled" ...>

[maxkatz6]

Closing as by design. With options to redefine behavior.

[timunie]

@maxkatz6 do you think simple theme should be changed to follow FluentTheme here or not?