QueryAccessibilityHelpEventArgs Class

Provides data for the QueryAccessibilityHelp event.

Namespace:  System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)

[ComVisibleAttribute(true)]
public class QueryAccessibilityHelpEventArgs : EventArgs

The Control class exposes a public QueryAccessibilityHelp event. You can use the properties of the QueryAccessibilityHelpEventArgs class to return custom help for a particular control to an accessible client, such as a screen reader. When you handle the QueryAccessibilityHelp event, you must set the values of the HelpNamespace, HelpKeyword, and HelpString properties to appropriate values.

NoteNote:

The HelpKeyword property should be a string representation of a numeric Help topic ID.

The following code example demonstrates the creation of an accessibility-aware chart control, using the AccessibleObject and Control.ControlAccessibleObject classes to expose accessible information. The control plots two curves along with a legend. The ChartControlAccessibleObject class, which derives from ControlAccessibleObject, is used in the CreateAccessibilityInstance method to provide custom accessible information for the chart control. Because the chart legend is not an actual Control-based control, but instead is drawn by the chart control, it does not any built-in accessible information. Because of this, the ChartControlAccessibleObject class overrides the GetChild method to return the CurveLegendAccessibleObject that represents accessible information for each part of the legend. When an accessible-aware application uses this control, the control can provide the necessary accessible information.

This example demonstrates using the QueryAccessibilityHelpEventArgs class with the QueryAccessibilityHelp event. See the AccessibleObject class overview for the complete code example.

// Handles the QueryAccessibilityHelp event. 
private void ChartControl_QueryAccessibilityHelp(object sender, 
                            System.Windows.Forms.QueryAccessibilityHelpEventArgs e)
{            
    e.HelpString = "Displays chart data";
}          

System.Object
  System.EventArgs
    System.Windows.Forms.QueryAccessibilityHelpEventArgs

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0
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