Subscribe to UI Automation Events
This topic shows how to subscribe to events raised by UI Automation providers.
Example
The following example code registers an event handler for the event that is raised when a control such as a button is invoked, and removes it when the application form closes. The event is identified by an AutomationEvent passed as a parameter to AddAutomationEventHandler.
// Member variables.
AutomationElement ElementSubscribeButton;
AutomationEventHandler UIAeventHandler;
/// <summary>
/// Register an event handler for InvokedEvent on the specified element.
/// </summary>
/// <param name="elementButton">The automation element.</param>
public void SubscribeToInvoke(AutomationElement elementButton)
{
if (elementButton != null)
{
Automation.AddAutomationEventHandler(InvokePattern.InvokedEvent,
elementButton, TreeScope.Element,
UIAeventHandler = new AutomationEventHandler(OnUIAutomationEvent));
ElementSubscribeButton = elementButton;
}
}
/// <summary>
/// AutomationEventHandler delegate.
/// </summary>
/// <param name="src">Object that raised the event.</param>
/// <param name="e">Event arguments.</param>
private void OnUIAutomationEvent(object src, AutomationEventArgs e)
{
// Make sure the element still exists. Elements such as tooltips
// can disappear before the event is processed.
AutomationElement sourceElement;
try
{
sourceElement = src as AutomationElement;
}
catch (ElementNotAvailableException ex)
{
return;
}
if (e.EventId == InvokePattern.InvokedEvent)
{
// TODO Add handling code.
}
else
{
// TODO Handle any other events that have been subscribed to.
}
}
private void ShutdownUIA()
{
if (UIAeventHandler != null)
{
Automation.RemoveAutomationEventHandler(InvokePattern.InvokedEvent,
ElementSubscribeButton, UIAeventHandler);
}
}
' Member variables.
Private ElementSubscribeButton As AutomationElement
Private UIAeventHandler As AutomationEventHandler
''' <summary>
''' Register an event handler for InvokedEvent on the specified element.
''' </summary>
''' <param name="elementButton">The automation element.</param>
Public Sub SubscribeToInvoke(ByVal elementButton As AutomationElement)
If (elementButton IsNot Nothing) Then
UIAeventHandler = New AutomationEventHandler(AddressOf OnUIAutomationEvent)
Automation.AddAutomationEventHandler(InvokePattern.InvokedEvent, elementButton, _
TreeScope.Element, UIAeventHandler)
ElementSubscribeButton = elementButton
End If
End Sub 'SubscribeToInvoke
''' <summary>
''' AutomationEventHandler delegate.
''' </summary>
''' <param name="src">Object that raised the event.</param>
''' <param name="e">Event arguments.</param>
Private Sub OnUIAutomationEvent(ByVal src As Object, ByVal e As AutomationEventArgs)
' Make sure the element still exists. Elements such as tooltips can disappear
' before the event is processed.
Dim sourceElement As AutomationElement
Try
sourceElement = DirectCast(src, AutomationElement)
Catch ex As ElementNotAvailableException
Exit Sub
End Try
If e.EventId Is InvokePattern.InvokedEvent Then
' TODO Add handling code.
Else
End If
' TODO Handle any other events that have been subscribed to.
Console.WriteLine("Event: " & e.EventId.ProgrammaticName)
End Sub 'OnUIAutomationEvent
Private Sub ShutdownUIA()
If (UIAeventHandler IsNot Nothing) Then
Automation.RemoveAutomationEventHandler(InvokePattern.InvokedEvent, ElementSubscribeButton, UIAeventHandler)
End If
End Sub 'ShutdownUIA
The following example shows how to use Microsoft UI Automation to subscribe to an event that is raised when the focus changes. The event handler is unregistered in a method that could be called on application shutdown, or when notification of UI events is no longer required.
AutomationFocusChangedEventHandler focusHandler = null;
/// <summary>
/// Create an event handler and register it.
/// </summary>
public void SubscribeToFocusChange()
{
focusHandler = new AutomationFocusChangedEventHandler(OnFocusChange);
Automation.AddAutomationFocusChangedEventHandler(focusHandler);
}
/// <summary>
/// Handle the event.
/// </summary>
/// <param name="src">Object that raised the event.</param>
/// <param name="e">Event arguments.</param>
private void OnFocusChange(object src, AutomationFocusChangedEventArgs e)
{
// TODO Add event handling code.
// The arguments tell you which elements have lost and received focus.
}
/// <summary>
/// Cancel subscription to the event.
/// </summary>
public void UnsubscribeFocusChange()
{
if (focusHandler != null)
{
Automation.RemoveAutomationFocusChangedEventHandler(focusHandler);
}
}
Private focusHandler As AutomationFocusChangedEventHandler = Nothing
''' <summary>
''' Create an event handler and register it.
''' </summary>
Public Sub SubscribeToFocusChange()
focusHandler = New AutomationFocusChangedEventHandler(AddressOf OnFocusChange)
Automation.AddAutomationFocusChangedEventHandler(focusHandler)
End Sub 'SubscribeToFocusChange
''' <summary>
''' Handle the event.
''' </summary>
''' <param name="src">Object that raised the event.</param>
''' <param name="e">Event arguments.</param>
Private Sub OnFocusChange(ByVal src As Object, ByVal e As AutomationFocusChangedEventArgs)
End Sub 'OnFocusChange
' TODO Add event handling code.
' The arguments tell you which elements have lost and received focus.
''' <summary>
''' Cancel subscription to the event.
''' </summary>
Public Sub UnsubscribeFocusChange()
If (focusHandler IsNot Nothing) Then
Automation.RemoveAutomationFocusChangedEventHandler(focusHandler)
End If
End Sub 'UnsubscribeFocusChange
See Also
Reference
AddAutomationEventHandler
RemoveAllEventHandlers
RemoveAutomationEventHandler