AspectRatio

Overview

AspectRatio (NaviusAspectRatio) is a ContentControl overriding MeasureOverride to enforce a fixed width:height ratio on its single child. It is a pure layout primitive: there is no CSS cascade to replicate in WPF, so the child fills the computed box directly via the default ContentPresenter rather than needing a separate inner element.

Usage

xmlns:navius="clr-namespace:Navius.Wpf.Primitives.Controls;assembly=Navius.Wpf.Primitives"

<navius:NaviusAspectRatio Ratio="1.7777">
    <Image Source="banner.png" Stretch="UniformToFill" />
</navius:NaviusAspectRatio>

Properties

Property	Type	Default	From	Description
Ratio	double	1.0	NaviusAspectRatio	Desired width:height ratio.
EffectiveRatio	double	computed	NaviusAspectRatio	Read-only, not a DP. Ratio if positive, else 1.0.
Content	object	-	ContentControl	The single child, filled into the computed box via the default ContentPresenter; there is no separate inner element the way the web has an inner <div>.

UIA mechanism

NaviusAspectRatio.cs has no OnCreateAutomationPeer() override; the web contract renders no ARIA role or aria-* attribute either, so the parity doc’s own WPF strategy states no automation-peer role mapping is needed beyond whatever default ContentControl supplies. The width-vs-height-driven box math (NaviusAspectRatioMath.ComputeDesiredSize) is factored out into a pure static method and unit-tested headless with plain [Fact]s, with no live Control/Application required.

Web deltas

• The web’s padding-bottom percentage-hack (an outer/inner <div> pair) has no WPF equivalent; this is a single ContentControl overriding MeasureOverride, computing the box directly rather than via a CSS trick.
• ForwardedAttributes/style-merge (the web’s “spread the consumer’s style, then append positioning last”) has no port: the single child simply fills the computed box via the default ContentPresenter.
• Width drives height whenever available width is finite (Width / EffectiveRatio, the direct analog of the web’s width:100%;padding-bottom:% hack). When width is infinite but height is finite, height instead drives width (Height * EffectiveRatio); when both are infinite, the box collapses to (0, 0). The web version is purely width-driven since a browser never presents an infinite-width layout, so the height-driven and both-infinite branches are WPF-specific additions with no web behavior to diverge from.

Captures

The AspectRatio Gallery page rendered at the pinned commit, in each theme.