dotnet-accessibility（点网可访问性）

dotnet-accessibility

Cross-platform accessibility patterns for.NET UI frameworks: semantic markup, keyboard navigation, focus management, color contrast, and screen reader integration. In-depth coverage for Blazor (HTML ARIA), MAUI (SemanticProperties), and WinUI (AutomationProperties / UI Automation). Brief guidance with cross-references for WPF, Uno Platform, and TUI frameworks.

Scope boundary: This skill owns cross-cutting accessibility principles and per-framework accessibility APIs. Framework-specific development patterns (project setup, MVVM, routing, deployment) are owned by the respective framework skills.

Out of scope: Framework project setup -- see individual framework skills. Legal compliance advice -- this skill references WCAG standards but does not provide legal guidance. UI framework selection -- see [skill:dotnet-ui-chooser].

Cross-references: [skill:dotnet-blazor-patterns] for Blazor hosting and render modes, [skill:dotnet-blazor-components] for Blazor component lifecycle, [skill:dotnet-maui-development] for MAUI patterns, [skill:dotnet-winui] for WinUI 3 patterns, [skill:dotnet-wpf-modern] for WPF on.NET 8+, [skill:dotnet-uno-platform] for Uno Platform patterns, [skill:dotnet-terminal-gui] for Terminal.Gui, [skill:dotnet-spectre-console] for Spectre.Console, [skill:dotnet-ui-chooser] for framework selection.

Cross-Platform Principles

These principles apply across all.NET UI frameworks. Framework-specific implementations follow in subsequent sections.

Semantic Markup

Provide meaningful names and descriptions for all interactive and informational elements. Screen readers rely on semantic metadata -- not visual appearance -- to convey UI structure.

• Every interactive control must have an accessible name (text label, ARIA label, or automation property)
• Images and icons must have text alternatives describing their purpose
• Decorative elements should be hidden from the accessibility tree
• Group related controls logically so screen readers announce them in context

Keyboard Navigation

All functionality must be operable via keyboard alone. Users who cannot use a mouse, pointer, or touch depend entirely on keyboard interaction.

• Maintain a logical tab order that follows the visual reading flow
• Provide visible focus indicators on all interactive elements
• Support standard keyboard patterns: Tab/Shift+Tab for navigation, Enter/Space for activation, Escape to dismiss, arrow keys within composite controls
• Avoid keyboard traps -- users must be able to navigate away from every control

Focus Management

Programmatic focus management ensures screen readers announce context changes correctly.

• Move focus to newly revealed content (dialogs, expanded panels, inline notifications)
• Return focus to the triggering element when dismissing overlays
• Avoid stealing focus unexpectedly during background updates
• Set initial focus on the primary action when a page or dialog loads

Color Contrast

Ensure text and interactive elements meet WCAG contrast ratios.

• Do not rely on color alone to convey information (use icons, patterns, or text labels as supplements)
• Support high-contrast themes and system color overrides
• Test with color blindness simulation tools

Blazor Accessibility (In-Depth)

Blazor renders HTML, so standard web accessibility patterns apply. Use native HTML semantics and ARIA attributes to build accessible Blazor apps.

Semantic HTML and ARIA

@* Use semantic HTML elements for structure *@
<nav aria-label="Main navigation">
    <ul>
        <li><a href="/products">Products</a></li>
        <li><a href="/about">About</a></li>
    </ul>
</nav>

<main>
    <h1>Product Catalog</h1>

    @* Image with alt text *@
    <img src="hero.png" alt="Product showcase displaying three featured items" />

    @* Decorative image hidden from accessibility tree *@
    <img src="divider.svg" alt="" role="presentation" />

    @* Button with accessible name from content *@
    <button @onclick="AddToCart">Add to Cart</button>

    @* Icon button requires aria-label *@
    <button @onclick="ToggleFavorite" aria-label="Add to favorites">
        <span class="icon-heart" aria-hidden="true"></span>
    </button>
</main>

Keyboard Event Handling

<div role="listbox"
     tabindex="0"
     aria-label="Product list"
     aria-activedescendant="@_activeId"
     @onkeydown="HandleKeyDown"
     @onkeydown:preventDefault>
    @foreach (var product in Products)
    {
        <div id="@($"product-{product.Id}")"
             role="option"
             aria-selected="@(product.Id == SelectedId)"
             @onclick="() => Select(product)">
            @product.Name
        </div>
    }
</div>

@code {
    private string _activeId = "";

    private void HandleKeyDown(KeyboardEventArgs e)
    {
        switch (e.Key)
        {
            case "ArrowDown":
                MoveSelection(1);
                break;
            case "ArrowUp":
                MoveSelection(-1);
                break;
            case "Enter":
            case " ":
                ConfirmSelection();
                break;
        }
    }
}

Live Regions

Announce dynamic content changes to screen readers without moving focus:

@* Polite: announced after current speech finishes *@
<div aria-live="polite" aria-atomic="true">
    @if (_statusMessage is not null)
    {
        <p>@_statusMessage</p>
    }
</div>

@* Assertive: interrupts current speech (use sparingly) *@
<div aria-live="assertive" role="alert">
    @if (_errorMessage is not null)
    {
        <p>@_errorMessage</p>
    }
</div>

Form Accessibility

<EditForm Model="@_model" OnValidSubmit="HandleSubmit">
    <DataAnnotationsValidator />

    <div>
        <label for="product-name">Product name</label>
        <InputText id="product-name"
                   @bind-Value="_model.Name"
                   aria-describedby="name-error"
                   aria-invalid="@(_nameInvalid ? "true" : null)" />
        <ValidationMessage For="() => _model.Name" id="name-error" />
    </div>

    <div>
        <label for="quantity">Quantity</label>
        <InputNumber id="quantity"
                     @bind-Value="_model.Quantity"
                     aria-describedby="quantity-help"
                     min="1" max="100" />
        <span id="quantity-help">Enter a value between 1 and 100</span>
    </div>

    <button type="submit">Submit Order</button>
</EditForm>

For Blazor hosting models and render mode configuration, see [skill:dotnet-blazor-patterns]. For component lifecycle and EditForm patterns, see [skill:dotnet-blazor-components].

MAUI Accessibility (In-Depth)

MAUI provides the SemanticProperties attached properties as the recommended accessibility API. These map to native platform accessibility APIs (VoiceOver on iOS/macOS, TalkBack on Android, Narrator on Windows).

SemanticProperties

<!-- Description: primary screen reader announcement -->
<Image Source="product.png"
       SemanticProperties.Description="Product photo showing a blue widget" />

<!-- Hint: additional context about an action -->
<Button Text="Add to Cart"
        SemanticProperties.Hint="Adds the current product to your shopping cart" />

<!-- HeadingLevel: enables heading-based navigation -->
<Label Text="Order Summary"
       SemanticProperties.HeadingLevel="Level1" />
<Label Text="Items"
       SemanticProperties.HeadingLevel="Level2" />

Key APIs:

• SemanticProperties.Description -- short text the screen reader announces (equivalent to accessibilityLabel on iOS, contentDescription on Android)
• SemanticProperties.Hint -- additional purpose context (equivalent to accessibilityHint on iOS)
• SemanticProperties.HeadingLevel -- marks headings (Level1 through Level9); Android and iOS only support a single heading level, Windows supports all 9

Platform warning: Do not set SemanticProperties.Description on a Label -- it overrides the Text property for screen readers, creating a mismatch between visual and spoken text. Do not set SemanticProperties.Description on Entry or Editor on Android -- use Placeholder or SemanticProperties.Hint instead, because Description conflicts with TalkBack actions.

Legacy AutomationProperties

AutomationProperties are the older Xamarin.Forms API, superseded by SemanticProperties in MAUI. Use SemanticProperties for new code.

AutomationProperties.IsInAccessibleTree and AutomationProperties.ExcludedWithChildren remain useful for controlling accessibility tree inclusion.

Programmatic Focus and Announcements

// Move screen reader focus to a specific element
myLabel.SetSemanticFocus();

// Announce text to the screen reader without moving focus
SemanticScreenReader.Default.Announce("Item added to cart successfully.");

Accessible Custom Controls

When building custom controls, ensure accessibility metadata is set:

public class RatingControl : ContentView
{
    private int _rating;

    public int Rating
    {
        get => _rating;
        set
        {
            _rating = value;
            SemanticProperties.SetDescription(this,
                $"Rating: {value} out of 5 stars");
            SemanticScreenReader.Default.Announce(
                $"Rating changed to {value} stars");
        }
    }
}

For MAUI project structure, MVVM patterns, and platform services, see [skill:dotnet-maui-development].

WinUI Accessibility (In-Depth)

WinUI 3 / Windows App SDK builds on the Microsoft UI Automation framework. Built-in controls include automation support by default. Custom controls need automation peers.

AutomationProperties

<!-- Name: primary accessible name for screen readers -->
<Image Source="ms-appx:///Assets/product.png"
       AutomationProperties.Name="Product photo showing a blue widget" />

<!-- HelpText: supplementary description -->
<Button Content="Add to Cart"
        AutomationProperties.HelpText="Adds the current product to your shopping cart" />

<!-- LabeledBy: associates a label with a control -->
<TextBlock x:Name="QuantityLabel" Text="Quantity:" />
<NumberBox AutomationProperties.LabeledBy="{x:Bind QuantityLabel}"
           Value="{x:Bind ViewModel.Quantity, Mode=TwoWay}" />

<!-- Hide decorative elements from accessibility tree -->
<Image Source="ms-appx:///Assets/divider.png"
       AutomationProperties.AccessibilityView="Raw" />

Custom Automation Peers

For custom controls, implement an AutomationPeer to expose the control to UI Automation clients:

// Custom control
public sealed class StarRating : Control
{
    public int Value
    {
        get => (int)GetValue(ValueProperty);
        set => SetValue(ValueProperty, value);
    }

    public static readonly DependencyProperty ValueProperty =
        DependencyProperty.Register(nameof(Value), typeof(int),
            typeof(StarRating), new PropertyMetadata(0, OnValueChanged));

    private static void OnValueChanged(DependencyObject d,
        DependencyPropertyChangedEventArgs e)
    {
        if (FrameworkElementAutomationPeer
                .FromElement((StarRating)d) is StarRatingAutomationPeer peer)
        {
            peer.RaiseValueChanged((int)e.OldValue, (int)e.NewValue);
        }
    }

    protected override AutomationPeer OnCreateAutomationPeer()
        => new StarRatingAutomationPeer(this);
}

// Automation peer (using Microsoft.UI.Xaml.Automation.Provider)
public sealed class StarRatingAutomationPeer
    : FrameworkElementAutomationPeer, IRangeValueProvider
{
    private StarRating Owner => (StarRating)base.Owner;

    public StarRatingAutomationPeer(StarRating owner) : base(owner) { }

    protected override string GetClassNameCore() => nameof(StarRating);
    protected override string GetNameCore()
        => $"Rating: {Owner.Value} out of 5 stars";
    protected override AutomationControlType GetAutomationControlTypeCore()
        => AutomationControlType.Slider;

    // IRangeValueProvider
    public double Value => Owner.Value;
    public double Minimum => 0;
    public double Maximum => 5;
    public double SmallChange => 1;
    public double LargeChange => 1;
    public bool IsReadOnly => false;

    public void SetValue(double value)
        => Owner.Value = (int)Math.Clamp(value, Minimum, Maximum);

    public void RaiseValueChanged(int oldValue, int newValue)
    {
        RaisePropertyChangedEvent(
            RangeValuePatternIdentifiers.ValueProperty,
            (double)oldValue, (double)newValue);
    }
}

Keyboard Accessibility in WinUI

WinUI XAML controls provide built-in keyboard support. Ensure custom controls follow the same patterns:

<!-- TabIndex controls navigation order -->
<TextBox Header="First name" TabIndex="1" />
<TextBox Header="Last name" TabIndex="2" />
<Button Content="Submit" TabIndex="3" />

<!-- AccessKey provides keyboard shortcuts (Alt + key) -->
<Button Content="Save" AccessKey="S" />
<Button Content="Delete" AccessKey="D" />

For WinUI project setup, XAML patterns, and Windows integration, see [skill:dotnet-winui].

WPF Accessibility (Brief)

WPF on.NET 8+ uses the same UI Automation framework as WinUI. The APIs are nearly identical with namespace differences.

• AutomationProperties.Name, AutomationProperties.HelpText, AutomationProperties.LabeledBy work the same as in WinUI
• Custom controls override OnCreateAutomationPeer() and return a FrameworkElementAutomationPeer subclass
• WPF Fluent theme (.NET 9+) includes high-contrast support automatically
• Use AutomationProperties.LiveSetting for live region announcements

<!-- WPF accessibility follows the same pattern as WinUI -->
<Image Source="product.png"
       AutomationProperties.Name="Product photo" />

<TextBlock x:Name="StatusLabel"
           AutomationProperties.LiveSetting="Polite"
           Text="{Binding StatusText}" />

For WPF development patterns on.NET 8+, see [skill:dotnet-wpf-modern].

Uno Platform Accessibility (Brief)

Uno Platform follows UWP/WinUI AutomationProperties patterns since its API surface is WinUI-compatible.

• AutomationProperties.Name, AutomationProperties.HelpText, AutomationProperties.LabeledBy work cross-platform
• Custom AutomationPeer implementations follow the WinUI pattern
• On WebAssembly, Uno maps AutomationProperties to HTML ARIA attributes automatically
• Platform-specific behavior may vary -- test on each target (Windows, iOS, Android, WASM)

For Uno Platform development patterns, see [skill:dotnet-uno-platform]. For per-target deployment and testing, see [skill:dotnet-uno-targets].

TUI Accessibility (Brief)

Terminal UI frameworks have inherent accessibility limitations. Screen reader support depends on the terminal emulator and operating system.

Terminal.Gui (v2):

• Screen readers can read terminal text content via the terminal emulator's accessibility support
• No programmatic accessibility API equivalent to ARIA or AutomationProperties
• Logical tab order follows the TabIndex property on views
• High contrast is managed by terminal color themes, not the app

Spectre.Console:

• Output-only library -- screen readers read terminal text buffer directly
• Use plain text fallbacks for complex visual elements (tables, trees) when accessibility is critical
• AnsiConsole.Profile.Capabilities can detect terminal features but not screen reader presence

Honest constraint: TUI apps cannot programmatically control screen reader behavior. Terminal emulators provide varying levels of accessibility support. For applications where accessibility is a hard requirement, consider a GUI framework (Blazor, MAUI, WinUI) instead.

For Terminal.Gui patterns, see [skill:dotnet-terminal-gui]. For Spectre.Console patterns, see [skill:dotnet-spectre-console].

Accessibility Testing Tools

Per-Platform Testing

Automated Testing Integration

// Blazor: integrate axe-core with Playwright for automated accessibility testing
// Requires: Deque.AxeCore.Playwright NuGet package
// Install: dotnet add package Deque.AxeCore.Playwright
var axeResults = await new Deque.AxeCore.Playwright.AxeBuilder(page)
    .AnalyzeAsync();

// Check for violations
Assert.Empty(axeResults.Violations);

// WinUI/WPF: use Accessibility Insights for Windows CLI in CI pipelines
// Requires: AccessibilityInsights.CLI (available via Microsoft Store or direct download)

Manual Testing Checklist

1. Keyboard-only navigation -- tab through entire app without mouse; verify all functionality is reachable
2. Screen reader walkthrough -- enable Narrator/VoiceOver/TalkBack and navigate the full workflow
3. High contrast -- enable system high-contrast theme and verify all content remains visible
4. Zoom/scaling -- increase text size to 200% and verify layout does not break or clip content
5. Color contrast -- verify all text and interactive elements meet WCAG AA ratios (4.5:1 for text, 3:1 for large text and UI components)

WCAG Reference

This skill references the Web Content Accessibility Guidelines (WCAG) as the global accessibility standard. WCAG 2.1 is the current baseline; WCAG 2.2 adds additional criteria for mobile and cognitive accessibility.

Four principles (POUR):

1. Perceivable -- information must be presentable in ways all users can perceive
2. Operable -- UI components must be operable by all users
3. Understandable -- information and UI operation must be understandable
4. Robust -- content must be robust enough to work with assistive technologies

Conformance levels: A (minimum), AA (recommended target for most apps), AAA (enhanced). Most legal requirements and industry standards target WCAG 2.1 Level AA.

Note: This skill provides technical implementation guidance. It does not constitute legal advice regarding accessibility compliance requirements, which vary by jurisdiction and application type.

Agent Gotchas

1. Do not set SemanticProperties.Description on MAUI Label controls. It overrides the Text property for screen readers, causing a mismatch between visual and spoken content. Labels are already accessible via their Text property.
2. Do not set SemanticProperties.Description on MAUI Entry/Editor on Android. Use Placeholder or SemanticProperties.Hint instead -- Description conflicts with TalkBack actions on these controls.
3. Do not use AutomationProperties.Name or AutomationProperties.HelpText for new MAUI code. Use SemanticProperties instead (the MAUI-native API). AutomationProperties.IsInAccessibleTree and ExcludedWithChildren remain valid for controlling accessibility tree inclusion.
4. Do not omit aria-label on icon-only Blazor buttons. Buttons without visible text content are invisible to screen readers unless aria-label or aria-labelledby is set.
5. Do not use aria-live="assertive" for routine status updates. Assertive interrupts the screen reader immediately. Use aria-live="polite" for non-critical updates; reserve assertive for errors and time-critical alerts.
6. Do not assume TUI apps are accessible by default. Terminal screen reader support varies dramatically by emulator and OS. Always provide alternative output formats for critical accessibility scenarios.
7. Do not hardcode colors without verifying contrast ratios. Use tools (Accessibility Insights, Lighthouse) to verify WCAG AA compliance. System high-contrast themes must also be tested.
8. Do not forget AccessKey on frequently used WinUI/WPF buttons. Access keys (Alt+key shortcuts) are essential for keyboard-dependent users and are trivial to add.

Prerequisites

• .NET 8.0+ (baseline for all frameworks)
• Framework-specific SDKs: MAUI workload, Windows App SDK (WinUI), Blazor project template
• Testing tools: Accessibility Insights (Windows), axe-core (web), Xcode Accessibility Inspector (macOS/iOS)
• Screen readers for manual testing: Narrator (Windows), VoiceOver (macOS/iOS), TalkBack (Android), NVDA (Windows, free)

References

• WCAG 2.1 Guidelines
• WCAG 2.2 Guidelines
• MAUI Accessibility (SemanticProperties)
• WinUI Accessibility Overview
• Blazor Accessibility
• UI Automation Overview
• Accessibility Insights
• axe-core (Deque)