[iOS] Fix ScrollView not expanding to full width in landscape when HorizontalOptions=FillAndExpand

[praveenkumarkarunanithi]

Root Cause

During the measure pass on iOS, the ScrollView handler calculated its size as the minimum of the inner content size and the available screen constraint. In landscape, although the available width increased (for example, from portrait to a wider constraint), the inner content had already measured itself at the smaller width. As a result, the ScrollView retained that earlier measured width and did not re-evaluate whether the content intended to stretch and fill the additional space. Unlike Android, the iOS implementation did not check whether the inner content had Fill alignment (which is the default for Grid and most layouts) after measurement. Because of this missing alignment evaluation, the ScrollView would shrink to content size instead of expanding to fill the available width when requested.

Description of Change

The iOS ScrollView handler’s measure logic was updated to align with Android behavior. After computing the initial size from content measurement, it now evaluates whether the inner content has Fill horizontal alignment. If so, and if the available width constraint is finite, the ScrollView expands to match the full available constraint. If the available constraint is infinite (such as when the ScrollView is placed inside a StackLayout or another unconstrained parent), the logic safely falls back to the measured content size to avoid invalid fill calculations. The adjustment is applied before explicit size overrides, ensuring that developer-defined Width, MinimumWidth, or MaximumWidth values continue to take precedence.

Issues Fixed

Fixes #20042

Tested the behaviour in the following platforms

• Android
• Windows
• iOS
• Mac

Note

Orientation change is not supported on Windows and MacCatalyst in this scenario, so the corresponding test case was not added for those platforms.

Output Video

Before Issue Fix	After Issue Fix
BeforeFix.22.mov	AfterFix.29.mov

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