[Bug] CollectionView Header cause delay to adding items.

[StevenGranados]

Description

Adding a header to a collectionview in the latest prerelease causes items to be delayed.

Steps to Reproduce

1. Click "add" button more than twice in attached repro.

Expected Behavior

In the repro if you click the add button it adds an "a" to the collectionview via an Observablecollection in a viewmodel. If i click it again I expect a "b".

Actual Behavior

I get an "a" the second time and a "b" the third time, as if delayed by one.

Basic Information

• Version with issue: 4.2.0.673161-pre3
• IDE: Visual Studio 2019
• Platform Target Frameworks:
  • Android: API 28

Reproduction Link

CollectionHeaderTest.zip

[jfversluis]

Confirmed this is happening. The other thing that I'm noticing is that the second a is added to the top. And from there all the b's are also added before the initial a.

The problem goes away when you take out the header. Not tested with iOS yet since the implementation was just done today.

Watch a (very slow) gif representation of this here:

[StevenGranados]

I changed the repro so it does numbers instead, so the problem is clearer.

[jfversluis]

Great, thank you!

In addition when I enable the selection mode and select an item, this also crashes because of the indices not being lined up correctly. Probably because of the header offset not taken into account.

/cc: @hartez