[Android] SpacingItemDecoration improvement

[kubaflo]

Description of Change

Vertical padding set on the recyclerView affected the rendering process. It is much more efficient to fully rely on ItemDecoration to manage spacing between items.

Issues Fixed

Fixes #24511
Fixes #8422
Fixes #18367
Fixes #17127

Before	After
Screen.Recording.2025-01-13.at.11.51.36.mov	Screen.Recording.2025-01-13.at.11.49.06.mov
Screen.Recording.2025-01-14.at.10.49.40.mov	Screen.Recording.2025-01-14.at.10.46.01.mov

[rmarinho]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[rmarinho]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[rmarinho]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[karthikraja-arumugam]

It also fixes the issue #18367

[kubaflo]

It also fixes the issue #18367

Thank you for letting me know!

[kcrg]

It would be really nice to get it in .NET 8 too <3

[rmarinho]

@kubaflo I re run but seems we have tests failing still . Can you look at this one CollectionViewWithSpacingShouldScroll ? Maybe screenshot is wrong?

also the other failures on iOS and cache one on Android seems it-s because this branch needs rebase on main. As main is green right now.

[kubaflo]

@rmarinho Done. Rebased and re-uploaded the screenshot.

[kubaflo]

It would be really nice to get it in .NET 8 too <3

Yeah sorry, but all the ongoing changes can only be in .NET 9

[rmarinho]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[mduchev]

Thank you very much for the fix of an issue that is at least 3 years old at this point.
When is this planned to get released?

[bcaceiro]

Also facing this issue -. in Android, the Scroll is not smooth and stops.

[bcaceiro]

Bumping this again - since it is performance related, and CV where so many users have issues :(

[hirurgaa]

Its so annoying to live with this issue for so many years!

[PureWeen]

/rebase

[Copilot]

Pull Request Overview

This PR improves the spacing behavior of CollectionView on Android by fully utilizing ItemDecoration for handling item spacing, thereby eliminating the unintended effects caused by vertical padding on the RecyclerView. Key changes include new test cases for Issue24511, updated spacing offset calculations in SpacingItemDecoration, and revised padding adjustments in MauiRecyclerView to account for grid orientation.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
TestCases.Shared.Tests/Tests/Issues/Issue24511.cs	Adds a UI test case to verify scrolling behavior with the improved spacing logic.
TestCases.HostApp/Issues/Issue24511.xaml.cs	Hosts the updated CollectionView with the new spacing approach and sample data.
TestCases.HostApp/Issues/Issue24511.xaml	Updates the CollectionView layout to support the new spacing mechanism.
Handlers/Items/Android/SpacingItemDecoration.cs	Revises the offset calculation logic for grid and linear layouts to remove external spacing around the RecyclerView.
Handlers/Items/Android/MauiRecyclerView.cs	Adjusts padding logic based on grid orientation to complement the new ItemDecoration implementation.

Comments suppressed due to low confidence (3)

src/Controls/src/Core/Handlers/Items/Android/SpacingItemDecoration.cs:99

• Consider adding tests for scenarios where the total number of items is not a multiple of the span value to ensure that the edge offsets are correctly applied for horizontal grids.

if (position < _span)

src/Controls/src/Core/Handlers/Items/Android/MauiRecyclerView.cs:484

• [nitpick] Review the new padding logic for horizontal grid layouts to ensure that setting the horizontal padding to zero does not inadvertently affect the layout in edge cases.

SetPadding(0, verticalPadding, 0, verticalPadding);

src/Controls/src/Core/Handlers/Items/Android/MauiRecyclerView.cs:489

• [nitpick] Verify that for vertical grid layouts the adjustment of horizontal padding exclusively via ItemDecoration does not leave behind unintended spacing at the outer edges.

SetPadding(horizontalPadding, 0, horizontalPadding, 0);

[mattleibow]

Looking good!

Just a nit on the double amount of code in the checks.

But also, maybe add another test for the grid in the other orientation just to make sure we are not missing anything.

[mattleibow]

This is different with the <. Is this intentional? This is a horizontal grid, which means it is a grid of _span rows or all the items in the first column. Which is basically column == 0?

[mattleibow]

Maybe this can be condensed into a single level where we just look at vertical/horizontal. I worry for the big block of code that is basically a duplicate. Then we also don't need the _itemsLayout field.

The grid has extra "steps", but a list basically has a span of 1.

This can maybe be condensed to a check of:

int rowCol = _span <= 1 ? position : position / _span;
int totalRowsCols = _span <= 1 ? itemCount : (int)Math.Ceiling((double)itemCount / _span);
int lastRowCol = totalRowsCols - 1;

if (linearItemsLayout.Orientation == ItemsLayoutOrientation.Vertical)
{
	if (rowCol == 0)
	{
		outRect.Top = 0;
	}
	else if (rowCol == lastRowCol)
	{
		outRect.Bottom = 0;
	}
}
else
{
	if (rowCol == 0)
	{
		outRect.Left = 0;
	}
	else if (rowCol == lastRowCol)
	{
		outRect.Right = 0;
	}
}

Screenshot added.