QueryAccessibilityHelpEventArgs Class
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QueryAccessibilityHelpEventArgs Class


Provides data for the QueryAccessibilityHelp event.

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


public class QueryAccessibilityHelpEventArgs : EventArgs


Initializes a new instance of the QueryAccessibilityHelpEventArgs class.

System_CAPS_pubmethodQueryAccessibilityHelpEventArgs(String, String, String)

Initializes a new instance of the QueryAccessibilityHelpEventArgs class.


Gets or sets the Help keyword for the specified control.


Gets or sets a value specifying the name of the Help file.


Gets or sets the string defining what Help to get for the AccessibleObject.


Determines whether the specified object is equal to the current object.(Inherited from Object.)


Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.(Inherited from Object.)


Serves as the default hash function. (Inherited from Object.)


Gets the Type of the current instance.(Inherited from Object.)


Creates a shallow copy of the current Object.(Inherited from Object.)


Returns a string that represents the current object.(Inherited from Object.)

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.


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";

.NET Framework
Available since 1.1

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

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