Change ComputeConstraintForView to return LayoutConstraint instead of using side effects

[Copilot]

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Fixes #31083

Summary

This PR refactors the ComputeConstraintForView method pattern across the MAUI layout system to eliminate side effects and improve code maintainability. Previously, ComputeConstraintForView was a void method that directly modified the child view's ComputedConstraint property. This change converts it to return a LayoutConstraint value instead, with the parent VisualElement responsible for assigning the returned value.

Key Changes

1. VisualElement Base Implementation

• Changed ComputeConstraintForView signature from protected virtual void to protected virtual LayoutConstraint
• Made ComputedConstraint setter internal (not private) to allow specific use cases like ViewCell
• Updated constraint computation flows to use return values:
  • ComputeConstrainsForChildren(): child.ComputedConstraint = ComputeConstraintForView(child)
  • OnChildAdded(): view.ComputedConstraint = ComputeConstraintForView(view)
  • InvalidateMeasureInternal(): thisView.ComputedConstraint = visualParent.ComputeConstraintForView(thisView)

2. Layout Override Updates

Updated all 11 layout classes to return constraints instead of setting them:

• ContentPresenter
• StackLayout, VerticalStackLayout, HorizontalStackLayout
• Grid (both modern and legacy versions)
• AbsoluteLayout
• TemplatedPage, TemplatedView
• ScrollView

3. Special Cases

Maintained direct constraint assignments where needed:

• ViewCell: Preserves constraint assignments in View property setter for cell layout behavior

Implementation Pattern

Before (side effects):

protected override void ComputeConstraintForView(View view)
{
    var result = LayoutConstraint.None;
    if (SomeCondition)
        result |= LayoutConstraint.HorizontallyFixed;
    
    view.ComputedConstraint = result; // Direct modification
}

After (return values):

protected override LayoutConstraint ComputeConstraintForView(View view)
{
    var result = LayoutConstraint.None;
    if (SomeCondition)
        result |= LayoutConstraint.HorizontallyFixed;
    
    return result; // Pure function
}

Benefits

1. Cleaner Architecture: Eliminates side effects making constraint computation logic easier to reason about
2. Better Encapsulation: Internal setter maintains access for specific scenarios while preventing unwanted modifications
3. Improved Testability: Pure functions are easier to unit test
4. Consistent Pattern: All constraint computation now follows the same return-value pattern

Compatibility

This change maintains full behavioral compatibility while improving the internal architecture. The constraint computation logic remains identical, only the mechanism for applying constraints has changed.

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[PureWeen]

@copilot keep this as protected

[Copilot]

Changed ComputeConstraintForView from internal back to protected as requested in commit b9138ec. This maintains the existing inheritance pattern for custom layouts while preserving the return value refactoring.

[Copilot]

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[PureWeen]

/azp run

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Pull Request Overview

This PR refactors the ComputeConstraintForView method pattern across the MAUI layout system to eliminate side effects and improve code architecture. Previously, this method was a void function that directly modified the child view's ComputedConstraint property, creating side effects that made the code harder to reason about and test.

Key changes:

• Changed ComputeConstraintForView from void to return LayoutConstraint value
• Updated all layout classes to return constraint values instead of setting them directly
• Modified calling code to assign the returned constraint value to the child's ComputedConstraint property

Reviewed Changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/Controls/src/Core/VisualElement/VisualElement.cs	Base implementation change from void to return LayoutConstraint, updated callers to assign returned value
src/Controls/src/Core/TemplatedView/TemplatedView.cs	Updated override to return constraint instead of setting directly
src/Controls/src/Core/TemplatedPage.cs	Updated override to return constraint instead of setting directly
src/Controls/src/Core/ScrollView/ScrollView.cs	Updated override to return constraint, added missing return for default case
src/Controls/src/Core/PublicAPI/*.txt	Updated public API signatures to reflect method signature change
src/Controls/src/Core/ListView/ListView.cs	Removed direct constraint assignment that's now handled by parent
src/Controls/src/Core/LegacyLayouts/StackLayout.cs	Updated overrides and internal calls to use return values
src/Controls/src/Core/LegacyLayouts/Grid.cs	Updated override to return constraint, fixed property change handler
src/Controls/src/Core/LegacyLayouts/AbsoluteLayout.cs	Updated override to return constraint, simplified early return logic
src/Controls/src/Core/Layout/VerticalStackLayout.cs	Updated override to return constraint instead of setting directly
src/Controls/src/Core/Layout/StackLayout.cs	Updated override to return constraint instead of setting directly
src/Controls/src/Core/Layout/HorizontalStackLayout.cs	Updated override to return constraint instead of setting directly
src/Controls/src/Core/Layout/Grid.cs	Updated override to return constraint instead of setting directly
src/Controls/src/Core/ContentPresenter.cs	Updated override to return constraint instead of setting directly

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[PureWeen]

/azp run

[PureWeen]

/azp run

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Azure Pipelines successfully started running 3 pipeline(s).

[PureWeen]

/azp run

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Azure Pipelines successfully started running 3 pipeline(s).

[PureWeen]

/azp run

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Azure Pipelines successfully started running 3 pipeline(s).

[PureWeen]

Entry failure is unrelated