Implementing Wpf Automation

WPF UI Automation Patterns

Implementing accessibility features using UI Automation framework.

Prerequisites

When implementing AutomationPeer for a CustomControl, ensure the control project is properly set up:

• ThemeInfo attribute in AssemblyInfo.cs → See /configuring-wpf-themeinfo
• CustomControl project structure → See /authoring-wpf-controls
• DefaultStyleKeyProperty in static constructor

1. UI Automation Overview

UI Automation Framework
├── Providers (Server-side)
│   ├── AutomationPeer (base class)
│   ├── FrameworkElementAutomationPeer
│   └── Custom AutomationPeers
├── Clients (Consumer-side)
│   ├── Screen readers (Narrator, JAWS)
│   ├── Testing tools
│   └── Custom automation clients
└── Automation Properties
    ├── AutomationProperties.Name
    ├── AutomationProperties.HelpText
    └── AutomationProperties.LabeledBy

2. AutomationProperties

2.1 Basic Properties

<!-- Name - primary identifier for screen readers -->
<Button Content="Submit"
        AutomationProperties.Name="Submit form"/>

<!-- Name for image buttons (no text content) -->
<Button AutomationProperties.Name="Close window">
    <Image Source="/Icons/close.png"/>
</Button>

<!-- HelpText - additional description -->
<TextBox AutomationProperties.Name="Email address"
         AutomationProperties.HelpText="Enter your email in format user@domain.com"/>

<!-- LabeledBy - reference to label element -->
<Label x:Name="UsernameLabel" Content="Username:"/>
<TextBox AutomationProperties.LabeledBy="{Binding ElementName=UsernameLabel}"/>

2.2 Additional Properties

<!-- AcceleratorKey - keyboard shortcut hint -->
<Button Content="_Save"
        AutomationProperties.AcceleratorKey="Ctrl+S"/>

<!-- AccessKey - mnemonic key -->
<Button Content="_File"
        AutomationProperties.AccessKey="Alt+F"/>

<!-- ItemStatus - current state information -->
<ListBoxItem AutomationProperties.ItemStatus="Selected, 3 of 10"/>

<!-- ItemType - type description for list items -->
<ListBoxItem AutomationProperties.ItemType="Email message"/>

<!-- LiveSetting - for dynamic content updates -->
<TextBlock AutomationProperties.LiveSetting="Polite"
           Text="{Binding StatusMessage}"/>

2.3 LiveSetting Values

3. Custom AutomationPeer

3.1 Basic Custom Peer

namespace MyApp.Controls;

using System.Windows;
using System.Windows.Automation.Peers;
using System.Windows.Controls;

public class RatingControl : Control
{
    public static readonly DependencyProperty ValueProperty = DependencyProperty.Register(
        nameof(Value), typeof(int), typeof(RatingControl),
        new PropertyMetadata(0));

    public int Value
    {
        get => (int)GetValue(ValueProperty);
        set => SetValue(ValueProperty, value);
    }

    public int MaxValue { get; set; } = 5;

    // Create custom AutomationPeer
    protected override AutomationPeer OnCreateAutomationPeer()
    {
        return new RatingControlAutomationPeer(this);
    }
}

public class RatingControlAutomationPeer : FrameworkElementAutomationPeer
{
    public RatingControlAutomationPeer(RatingControl owner)
        : base(owner)
    {
    }

    private RatingControl RatingControl => (RatingControl)Owner;

    // Return control type for screen readers
    protected override AutomationControlType GetAutomationControlTypeCore()
    {
        return AutomationControlType.Slider;
    }

    // Return class name
    protected override string GetClassNameCore()
    {
        return nameof(RatingControl);
    }

    // Return accessible name
    protected override string GetNameCore()
    {
        var name = base.GetNameCore();

        if (string.IsNullOrEmpty(name))
        {
            return $"Rating: {RatingControl.Value} of {RatingControl.MaxValue} stars";
        }

        return name;
    }

    // Return help text
    protected override string GetHelpTextCore()
    {
        return "Use arrow keys to change rating";
    }
}

Advanced: See ADVANCED.md for implementing automation patterns (IRangeValueProvider), raising automation events, keyboard navigation, and screen reader announcements.

4. Common Automation Patterns

5. Accessibility Checklist

Essential

• All interactive elements have AutomationProperties.Name
• Images have descriptive names or are marked decorative
• Form fields are labeled (LabeledBy or Name)
• Focus is visible and logical order is correct
• Keyboard navigation works for all functionality

Enhanced

• HelpText provides additional context
• AcceleratorKey documents shortcuts
• LiveSetting for dynamic content
• Custom controls have AutomationPeers
• Color contrast meets WCAG guidelines

6. Testing Accessibility

6.1 Using Inspect.exe

Tools location:
Windows SDK → bin → [arch] → inspect.exe

Usage:
1. Run inspect.exe
2. Hover over UI elements
3. View automation properties
4. Verify Name, ControlType, Patterns

6.2 Using Narrator

Windows + Ctrl + Enter: Toggle Narrator
Tab: Navigate forward
Shift + Tab: Navigate backward
Caps Lock + Up/Down: Read current item

7. References

• UI Automation Overview - Microsoft Docs
• AutomationProperties Class - Microsoft Docs
• Custom Control Accessibility - Microsoft Docs

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