QueryAccessibilityHelpEventHandler Delegate
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QueryAccessibilityHelpEventHandler Delegate


Represents the method that will handle the QueryAccessibilityHelp event of a control.

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

public delegate void QueryAccessibilityHelpEventHandler(
	object sender,
	QueryAccessibilityHelpEventArgs e


Type: System.Object

The source of the event.

Type: System.Windows.Forms.QueryAccessibilityHelpEventArgs

A QueryAccessibilityHelpEventArgs that contains the event data.

When you create a QueryAccessibilityHelpEventHandler delegate, you identify the method that will handle the event. To associate the event with your event handler, add an instance of the delegate to the event. The event handler is called whenever the event occurs, unless you remove the delegate. For more information about event-handler delegates, see NIB: Events and Delegates.

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 include 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 code demonstrates using the QueryAccessibilityHelpEventHandler delegate with the QueryAccessibilityHelp event. For the complete code example, see AccessibleObject.

// Overridden to return the custom AccessibleObject 
// for the entire chart.
protected override AccessibleObject CreateAccessibilityInstance() 
    return new ChartControlAccessibleObject(this);

.NET Framework
Available since 1.1
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