Control.QueryAccessibilityHelp Event

Occurs when AccessibleObject is providing help to accessibility applications.

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

event QueryAccessibilityHelpEventHandler^ QueryAccessibilityHelp {
	void add (QueryAccessibilityHelpEventHandler^ value);
	void remove (QueryAccessibilityHelpEventHandler^ value);
/** @event */
public void add_QueryAccessibilityHelp (QueryAccessibilityHelpEventHandler value)

/** @event */
public void remove_QueryAccessibilityHelp (QueryAccessibilityHelpEventHandler value)

JScript supports the use of events, but not the declaration of new ones.

You should use the HelpProvider class to enable users to invoke help on your accessible object by pressing the F1 key. Using the HelpProvider provides you with complete information in the QueryAccessibilityHelpEventArgs. For more information about handling events, see Consuming Events.

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. Since 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 code excerpt demonstrates handling the QueryAccessibilityHelp event. See the AccessibleObject class overview for the complete code example.

// Handles the QueryAccessibilityHelp event.
void ChartControl_QueryAccessibilityHelp( Object^ /*sender*/, System::Windows::Forms::QueryAccessibilityHelpEventArgs^ e )
   e->HelpString = "Displays chart data";

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

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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

.NET Framework

Supported in: 2.0, 1.1, 1.0