[Segmented] Left arrow key not propagating to parent when at leftmost item

[tomokuni]

Describe the bug

Title:
[Segmented] Left arrow key not propagating to parent when at leftmost item

Description:
When the focus is on the leftmost SegmentedItem in a Segmented control and the left arrow key (←) is pressed, the key event is consumed by the control instead of being propagated to the parent for XY focus navigation.

Current Behavior:

• Right arrow (→): Works correctly - when at the rightmost item, the key is NOT consumed and propagates to parent
• Left arrow (←): Does NOT work - when at the leftmost item, the key IS consumed and does NOT propagate to parent

Expected Behavior:
Both left and right arrow keys should behave symmetrically:

• When at the boundary, the key event should be propagated to the parent for XY focus navigation
• This allows focus to move to adjacent Segmented controls in parent containers

Root Cause:
In Segmented.cs, the MoveFocus(MoveDirection direction) method has asymmetric behavior:

The Bug:

• When at the left boundary, retVal = true is set, which means the key is marked as "handled"
• When at the right boundary, retVal is not modified (remains false), meaning the key is NOT marked as "handled"
• This asymmetry breaks XY focus navigation with multiple Segmented controls

Fix:
Remove the else { retVal = true; } block in the Previous direction case, or add equivalent handling for the Next direction:

Steps to reproduce

When the focus is on the leftmost `SegmentedItem` in a `Segmented` control and the left arrow key (←) is pressed, the key event is consumed by the control instead of being propagated to the parent for XY focus navigation.

Expected behavior

左右の矢印キーは対称的に動作すべきです:

• 境界位置では、XYフォーカスナビゲーションのためキーイベントを親に伝播する
• これにより、親コンテナ内の隣接するSegmentedコントロールへフォーカスが移動可能となる

Screenshots

No response

Code Platform

• UWP
• WinAppSDK / WinUI 3
• Web Assembly (WASM)
• Android
• iOS
• MacOS
• Linux / GTK

Windows Build Number

• Windows 10 1809 (Build 17763)
• Windows 10 1903 (Build 18362)
• Windows 10 1909 (Build 18363)
• Windows 10 2004 (Build 19041)
• Windows 10 20H2 (Build 19042)
• Windows 10 21H1 (Build 19043)
• Windows 10 21H2 (Build 19044)
• Windows 10 22H2 (Build 19045)
• Windows 11 21H2 (Build 22000)
• Other (specify)

Other Windows Build number

Windows11 25H2

App minimum and target SDK version

• Windows 10, version 1809 (Build 17763)
• Windows 10, version 1903 (Build 18362)
• Windows 10, version 1909 (Build 18363)
• Windows 10, version 2004 (Build 19041)
• Windows 10, version 2104 (Build 20348)
• Windows 11, version 22H2 (Build 22000)
• Other (specify)

Other SDK version

10.0.17763.0

Visual Studio Version

Preview

Visual Studio Build Number

Visual Studio 2026

Device form factor

Desktop

Additional context

No response

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