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QueryAccessibilityHelp Event

Control.QueryAccessibilityHelp Event

Occurs when AccessibleObject is providing help to accessibility applications.

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

public event QueryAccessibilityHelpEventHandler QueryAccessibilityHelp

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 Handling and Raising 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. 
private void ChartControl_QueryAccessibilityHelp(object sender, 
                            System.Windows.Forms.QueryAccessibilityHelpEventArgs e)
{            
    e.HelpString = "Displays chart data";
}          

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1
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