Add PreviewView support to ContextMenu for LongPressed mode

[Copilot]

Adds a PreviewView property to ContextMenu so consumers can display a fully custom MAUI view as a preview on long-press — intended for cases like document lists where titles are truncated in the list row.

Description of Change

• ContextMenu.PreviewView — new bindable View? property, only meaningful in LongPressed mode.

• iOS — ContextMenuPreviewViewController wraps the MAUI view as a UIViewController and is returned from the UIContextMenuConfiguration previewProvider lambda, giving the native "peek" experience above the context menu.

• Android — ContextMenuHandler shows the preview in a PopupWindow anchored above the element when the long-press triggers. The popup is wrapped in a FrameLayout with a MaterialShapeDrawable background (rounded corners, color_surface_default fill) and shadow elevation. The background is dimmed using FLAG_DIM_BEHIND with dimAmount = 0.5f to give a similar feel to the iOS peek experience. The popup is auto-dismissed via PopupMenu.IOnDismissListener.OnDismiss.

• Sample added to ContextMenuSamples.xaml demonstrating a long document title + subtitle in the preview with two menu actions.

Usage:

<dui:ListItem dui:ContextMenuEffect.Mode="LongPressed">
    <dui:ContextMenuEffect.Menu>
        <dui:ContextMenu>
            <dui:ContextMenu.PreviewView>
                <dui:Label Text="Full document title that would otherwise be truncated" />
            </dui:ContextMenu.PreviewView>
            <dui:ContextMenuItem Title="Open" />
            <dui:ContextMenuItem Title="Delete" IsDestructive="True" />
        </dui:ContextMenu>
    </dui:ContextMenuEffect.Menu>
</dui:ListItem>

Todos

• I have tested on an Android device.
• I have tested on an iOS device.
• I have supported accessibility

View original Slack conversation

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[haavamoa]

@copilot can you make sure the background gets dimmed / blurred on Android, and maybe add some shadow on the preview view? This will make it pop a bit more like it does on iOS.

[Copilot]

@copilot can you make sure the background gets dimmed / blurred on Android, and maybe add some shadow on the preview view? This will make it pop a bit more like it does on iOS.

Done in commit 1f1f110.

The ShowPreview() method on Android now:

• Shadow: Wraps the preview in a FrameLayout with a MaterialShapeDrawable background (rounded size_2 corners, color_surface_default fill) and size_3 elevation — this gives the Material shadow that makes the card pop.
• Dim: After ShowAsDropDown, grabs the popup's root window via WindowManager and sets FLAG_DIM_BEHIND with a dimAmount of 0.5f, darkening everything behind the preview card.