ItemsRepeater flicker when we data-bind the visibility of the items

[dr1rrb]

Current behavior

When we have a view like this:

<ItemsRepeater ItemsSource="{Binding MySource}">
    <ItemsRepeater.ItemTemplate>
        <DataTemplate>
            <Border>
                <TextBlock Text="{Binding Value}" Visiblity="{Binding IsVisible}" />
            </Border>
        </DataTemplate>
    </ItemsRepeater.ItemTemplate>
</ItemsRepeater>

Note the binding on Visiblity="{Binding IsVisible}" on the TextBlock.

This cause some flicker when scrolling, especially if there are nested ItemsRepeater doing the same!

Expected behavior

No flicker and proper alignment of items!

How to reproduce it (as minimally and precisely as possible)

Workaround

DO NOT Data-bind the visibility of items, instead remove and add them back to the MySource collection.

---

IMPORTANT

The "workaround" is actually the recommended way to do as it is (significantly) more performant as:

1. It avoids materialization of items that are finally hidden

2. Data-binding the visibility might (always?) cause an additional layouting pass!

Works on UWP/WinUI

None

NuGet package version(s)

5.2

Affected platforms

Uno ... but the issue might be the same on windows and should be tested first!

[Youssef1313]

@dr1rrb Is this about ItemsRepeaterManyItems sample? Are you testing Gtk or WPF?

For Gtk, it's a known problem which I tried to fix, but the fix broke Gallery canary so it was reverted. See https://github.com/unoplatform/uno/pull/15811

[Youssef1313]

I can try another fix though

[dr1rrb]

@dr1rrb Is this about ItemsRepeaterManyItems sample? Are you testing Gtk or WPF?

For Gtk, it's a known problem which I tried to fix, but the fix broke Gallery canary so it was reverted. See #15811

Eh eh no it was only to have an issue to track my time ... but since I now found the root cause I can rename it and add details :)

[ramezgerges]

This needs a more detailed information. I tried this but no flickering happened:

// in sample constructor:
ir.DataContext = Enumerable.Range(0, 1000).Select(i => new VM(i.ToString(), i % 2 == 0)).ToList();

public class VM
{
    private string value;
    private bool isVisible;

    public VM(string value, bool isVisible)
    {
        this.value = value;
        this.isVisible = isVisible;
    }
    public string Value => value;
    public bool IsVisible => isVisible;
}

<ScrollViewer Height="400">
      <ItemsRepeater x:Name="ir" ItemsSource="{Binding}">
        <ItemsRepeater.ItemTemplate>
          <DataTemplate>
            <Border Visibility="{Binding IsVisible}">
              <TextBlock Text="{Binding Value}" />
            </Border>
          </DataTemplate>
        </ItemsRepeater.ItemTemplate>
      </ItemsRepeater>
    </ScrollViewer>

However, there is some extreme corruption happening. Reported in https://github.com/unoplatform/uno/issues/16992

[dr1rrb]

However, there is some extreme corruption happening. Reported in #16992

That's what I call "flicker" since it's when you scroll (depending of the scroll direction you will be able to see some items or not). Closing https://github.com/unoplatform/uno/issues/16992 as duplicate of this.

Edit: Feel free to rename this issue if you find it not descriptive enough ;)