CacheRequest.Activate Methode
Definitie
Belangrijk
Bepaalde informatie heeft betrekking op een voorlopige productversie die aanzienlijk kan worden gewijzigd voordat deze wordt uitgebracht. Microsoft biedt geen enkele expliciete of impliciete garanties met betrekking tot de informatie die hier wordt verstrekt.
Hiermee stelt u dit CacheRequest in als de actieve specificatie voor de items die worden geretourneerd wanneer een AutomationElement item wordt aangevraagd op dezelfde thread.
public:
IDisposable ^ Activate();public IDisposable Activate();member this.Activate : unit -> IDisposablePublic Function Activate () As IDisposableRetouren
Het object dat kan worden gebruikt om de CacheRequest.
Voorbeelden
In het volgende voorbeeld ziet u hoe Activate u patronen en eigenschappen in de cache kunt opslaan.
/// <summary>
/// Caches and retrieves properties for a list item by using CacheRequest.Activate.
/// </summary>
/// <param name="elementList">Element from which to retrieve a child element.</param>
/// <remarks>
/// This code demonstrates various aspects of caching. It is not intended to be
/// an example of a useful method.
/// </remarks>
private void CachePropertiesByActivate(AutomationElement elementList)
{
AutomationElement elementListItem;
// Set up the request.
CacheRequest cacheRequest = new CacheRequest();
cacheRequest.Add(AutomationElement.NameProperty);
cacheRequest.Add(AutomationElement.IsEnabledProperty);
cacheRequest.Add(SelectionItemPattern.Pattern);
cacheRequest.Add(SelectionItemPattern.SelectionContainerProperty);
// Obtain an element and cache the requested items.
using (cacheRequest.Activate())
{
Condition cond = new PropertyCondition(AutomationElement.IsSelectionItemPatternAvailableProperty, true);
elementListItem = elementList.FindFirst(TreeScope.Children, cond);
}
// The CacheRequest is now inactive.
// Retrieve the cached property and pattern.
SelectionItemPattern pattern;
String itemName;
try
{
itemName = elementListItem.Cached.Name;
pattern = elementListItem.GetCachedPattern(SelectionItemPattern.Pattern) as SelectionItemPattern;
}
catch (InvalidOperationException)
{
Console.WriteLine("Object was not in cache.");
return;
}
// Alternatively, you can use TryGetCachedPattern to retrieve the cached pattern.
object cachedPattern;
if (true == elementListItem.TryGetCachedPattern(SelectionItemPattern.Pattern, out cachedPattern))
{
pattern = cachedPattern as SelectionItemPattern;
}
// Specified pattern properties are also in the cache.
AutomationElement parentList = pattern.Cached.SelectionContainer;
// The following line will raise an exception, because the HelpText property was not cached.
/*** String itemHelp = elementListItem.Cached.HelpText; ***/
// Similarly, pattern properties that were not specified in the CacheRequest cannot be
// retrieved from the cache. This would raise an exception.
/*** bool selected = pattern.Cached.IsSelected; ***/
// This is still a valid call, even though the property is in the cache.
// Of course, the cached value and the current value are not guaranteed to be the same.
itemName = elementListItem.Current.Name;
}
''' <summary>
''' Caches and retrieves properties for a list item by using CacheRequest.Activate.
''' </summary>
''' <param name="elementList">Element from which to retrieve a child element.</param>
''' <remarks>
''' This code demonstrates various aspects of caching. It is not intended to be
''' an example of a useful method.
''' </remarks>
Private Sub CachePropertiesByActivate(ByVal elementList As AutomationElement)
' Set up the request.
Dim myCacheRequest As New CacheRequest()
myCacheRequest.Add(AutomationElement.NameProperty)
myCacheRequest.Add(AutomationElement.IsEnabledProperty)
myCacheRequest.Add(SelectionItemPattern.Pattern)
myCacheRequest.Add(SelectionItemPattern.SelectionContainerProperty)
Dim elementListItem As AutomationElement
' Obtain an element and cache the requested items.
Using myCacheRequest.Activate()
Dim myCondition As New PropertyCondition( _
AutomationElement.IsSelectionItemPatternAvailableProperty, True)
elementListItem = elementList.FindFirst(TreeScope.Children, myCondition)
End Using
' The CacheRequest is now inactive.
' Retrieve the cached property and pattern.
Dim pattern As SelectionItemPattern
Dim itemName As String
Try
itemName = elementListItem.Cached.Name
pattern = DirectCast(elementListItem.GetCachedPattern(SelectionItemPattern.Pattern), _
SelectionItemPattern)
Catch ex As InvalidOperationException
Console.WriteLine("Object was not in cache.")
Return
End Try
' Alternatively, you can use TryGetCachedPattern to retrieve the cached pattern.
Dim cachedPattern As Object = Nothing
If True = elementListItem.TryGetCachedPattern(SelectionItemPattern.Pattern, cachedPattern) Then
pattern = DirectCast(cachedPattern, SelectionItemPattern)
End If
' Specified pattern properties are also in the cache.
Dim parentList As AutomationElement = pattern.Cached.SelectionContainer
' The following line will raise an exception, because the HelpText property was not cached.
'** String itemHelp = elementListItem.Cached.HelpText; **
' Similarly, pattern properties that were not specified in the CacheRequest cannot be
' retrieved from the cache. This would raise an exception.
'** bool selected = pattern.Cached.IsSelected; **
' This is still a valid call, even though the property is in the cache.
' Of course, the cached value and the current value are not guaranteed to be the same.
itemName = elementListItem.Current.Name
End Sub
Opmerkingen
Het gebruik van deze methode verdient meestal de voorkeur aan het gebruik Push en Pop als een middel om de CacheRequest. Het object wordt naar de stapel gepusht wanneer Activate het wordt aangeroepen en wordt vervolgens uitgelicht wanneer het wordt verwijderd. Plaats de retourwaarde binnen een using blok (Using in Visual Basic) om de verwijdering te garanderen.
