Automation.AddAutomationPropertyChangedEventHandler Method (AutomationElement, TreeScope, AutomationPropertyChangedEventHandler, AutomationProperty[])

 

Registers a method that will handle property-changed events.

Namespace:   System.Windows.Automation
Assembly:  UIAutomationClient (in UIAutomationClient.dll)

public static void AddAutomationPropertyChangedEventHandler(
	AutomationElement element,
	TreeScope scope,
	AutomationPropertyChangedEventHandler eventHandler,
	params AutomationProperty[] properties
)

Parameters

element
Type: System.Windows.Automation.AutomationElement

The UI Automation element with which to associate the event handler.

scope
Type: System.Windows.Automation.TreeScope

The scope of events to be handled; that is, whether they are on the element itself, or on its ancestors and children.

eventHandler
Type: System.Windows.Automation.AutomationPropertyChangedEventHandler

The method to call when the event occurs.

properties
Type: System.Windows.Automation.AutomationProperty[]

The UI Automation properties of interest.

The user interface (UI) item specified by the supplied UI Automation element might not support the properties specified by the properties parameter.

eventHandler can be an instance of the method, or a reference to the method (AddressOf in Visual Basic).

The following example code adds an event handler that listens for a change in the enabled state of a specified element.


AutomationPropertyChangedEventHandler propChangeHandler;
/// <summary>
/// Adds a handler for property-changed event; in particular, a change in the enabled state.
/// </summary>
/// <param name="element">The UI Automation element whose state is being monitored.</param>
public void SubscribePropertyChange(AutomationElement element)
{
    Automation.AddAutomationPropertyChangedEventHandler(element, 
        TreeScope.Element, 
        propChangeHandler = new AutomationPropertyChangedEventHandler(OnPropertyChange),
        AutomationElement.IsEnabledProperty);

}

/// <summary>
/// Handler for property changes.
/// </summary>
/// <param name="src">The source whose properties changed.</param>
/// <param name="e">Event arguments.</param>
private void OnPropertyChange(object src, AutomationPropertyChangedEventArgs e)
{
    AutomationElement sourceElement = src as AutomationElement;
    if (e.Property == AutomationElement.IsEnabledProperty)
    {
        bool enabled = (bool)e.NewValue;
        // TODO: Do something with the new value. 
        // The element that raised the event can be identified by its runtime ID property.
    }
    else
    { 
        // TODO: Handle other property-changed events.
    }
}

public void UnsubscribePropertyChange(AutomationElement element)
{
    if (propChangeHandler != null)
    {
        Automation.RemoveAutomationPropertyChangedEventHandler(element, propChangeHandler);
    }
}

.NET Framework
Available since 3.0
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