AutomationElement.TryGetCachedPattern(AutomationPattern, Object) 方法
定义
重要
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从缓存中检索控件模式。
public:
bool TryGetCachedPattern(System::Windows::Automation::AutomationPattern ^ pattern, [Runtime::InteropServices::Out] System::Object ^ % patternObject);public bool TryGetCachedPattern (System.Windows.Automation.AutomationPattern pattern, out object patternObject);member this.TryGetCachedPattern : System.Windows.Automation.AutomationPattern * obj -> boolPublic Function TryGetCachedPattern (pattern As AutomationPattern, ByRef patternObject As Object) As Boolean参数
- pattern
- AutomationPattern
要检索的控件模式的标识符。
- patternObject
- Object
返回时，如果模式在缓存中，则包含该模式；否则为 null。
返回
如果模式在缓存中，为 true；如果模式不在缓存中或不受支持，则为 false。
示例
以下示例演示如何缓存和检索控件模式。
/// <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