在 UI 自动化中使用缓存
备注
本文档适用于想要使用 System.Windows.Automation 命名空间中定义的托管 UI 自动化类的 .NET Framework 开发人员。 有关 UI 自动化的最新信息,请参阅 Windows 自动化 API:UI 自动化。
本部分演示如何实现 AutomationElement 属性和控件模式的缓存。
激活缓存请求
创建 CacheRequest。
使用 Add指定要缓存的属性和模式。
通过设置 TreeScope 属性来指定缓存的范围。
通过设置 TreeFilter 属性来指定子树视图。
如果想通过不检索对对象的完全引用来提高效率,请将 AutomationElementMode 属性设置为 None 。 (这将导致无法从那些对象中检索当前值。)
使用
using
块(Microsoft Visual Basic .NET 中的Using
)中的 Activate 激活请求。
在获得 AutomationElement 对象或订阅事件后,通过使用 Pop (如果使用了 Push )或处理 Activate创建的对象来禁用请求。 (使用 using
块(Microsoft Visual Basic .NET 中的 Using
)中的 Activate)。
缓存 AutomationElement 属性
当 CacheRequest 处于活动状态时,使用 AutomationElement 或 FindFirst 获取 FindAll对象,或者获取 AutomationElement 并将其作为 CacheRequest 处于活动状态时注册的事件的源。 (也可以通过下面的方法创建缓存:将 CacheRequest 传递给 GetUpdatedCache 或 TreeWalker 方法之一。)
使用 GetCachedPropertyValue 或从 Cached 的 AutomationElement属性中检索属性。
获取缓存模式及其属性
当 CacheRequest 处于活动状态时,使用 AutomationElement 或 FindFirst 获取 FindAll对象,或者获取 AutomationElement 并将其作为 CacheRequest 处于活动状态时注册的事件的源。 (也可以通过下面的方法创建缓存:将 CacheRequest 传递给 GetUpdatedCache 或 TreeWalker 方法之一。)
使用 GetCachedPattern 或 TryGetCachedPattern 检索缓存的模式。
控件模式的
Cached
属性中检索属性值。
示例 1
下面的代码示例使用 Activate 激活 CacheRequest,演示了缓存的各个方面。
/// <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
示例 2
下面的代码示例使用 Push 激活 CacheRequest,演示了缓存的各个方面。 除非希望嵌套缓存请求,否则最好是使用 Activate。
/// <summary>
/// Caches and retrieves properties for a list item by using CacheRequest.Push.
/// </summary>
/// <param name="autoElement">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 CachePropertiesByPush(AutomationElement elementList)
{
// Set up the request.
CacheRequest cacheRequest = new CacheRequest();
// Do not get a full reference to the cached objects, only to their cached properties and patterns.
cacheRequest.AutomationElementMode = AutomationElementMode.None;
// Cache all elements, regardless of whether they are control or content elements.
cacheRequest.TreeFilter = Automation.RawViewCondition;
// Property and pattern to cache.
cacheRequest.Add(AutomationElement.NameProperty);
cacheRequest.Add(SelectionItemPattern.Pattern);
// Activate the request.
cacheRequest.Push();
// Obtain an element and cache the requested items.
Condition cond = new PropertyCondition(AutomationElement.IsSelectionItemPatternAvailableProperty, true);
AutomationElement elementListItem = elementList.FindFirst(TreeScope.Children, cond);
// At this point, you could call another method that creates a CacheRequest and calls Push/Pop.
// While that method was retrieving automation elements, the CacheRequest set in this method
// would not be active.
// Deactivate the request.
cacheRequest.Pop();
// Retrieve the cached property and pattern.
String itemName = elementListItem.Cached.Name;
SelectionItemPattern pattern = elementListItem.GetCachedPattern(SelectionItemPattern.Pattern) as SelectionItemPattern;
// The following is an alternative way of retrieving the Name property.
itemName = elementListItem.GetCachedPropertyValue(AutomationElement.NameProperty) as String;
// This is yet another way, which returns AutomationElement.NotSupported if the element does
// not supply a value. If the second parameter is false, a default name is returned.
object objName = elementListItem.GetCachedPropertyValue(AutomationElement.NameProperty, true);
if (objName == AutomationElement.NotSupported)
{
itemName = "Unknown";
}
else
{
itemName = objName as String;
}
// The following call raises an exception, because only the cached properties are available,
// as specified by cacheRequest.AutomationElementMode. If AutomationElementMode had its
// default value (Full), this call would be valid.
/*** bool enabled = elementListItem.Current.IsEnabled; ***/
}
''' <summary>
''' Caches and retrieves properties for a list item by using CacheRequest.Push.
''' </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 CachePropertiesByPush(ByVal elementList As AutomationElement)
' Set up the request.
Dim cacheRequest As New CacheRequest()
' Do not get a full reference to the cached objects, only to their cached properties and patterns.
cacheRequest.AutomationElementMode = AutomationElementMode.None
' Cache all elements, regardless of whether they are control or content elements.
cacheRequest.TreeFilter = Automation.RawViewCondition
' Property and pattern to cache.
cacheRequest.Add(AutomationElement.NameProperty)
cacheRequest.Add(SelectionItemPattern.Pattern)
' Activate the request.
cacheRequest.Push()
' Obtain an element and cache the requested items.
Dim myCondition As New PropertyCondition(AutomationElement.IsSelectionItemPatternAvailableProperty, _
True)
Dim elementListItem As AutomationElement = elementList.FindFirst(TreeScope.Children, myCondition)
' At this point, you could call another method that creates a CacheRequest and calls Push/Pop.
' While that method was retrieving automation elements, the CacheRequest set in this method
' would not be active.
' Deactivate the request.
cacheRequest.Pop()
' Retrieve the cached property and pattern.
Dim itemName As String = elementListItem.Cached.Name
Dim pattern As SelectionItemPattern = _
DirectCast(elementListItem.GetCachedPattern(SelectionItemPattern.Pattern), SelectionItemPattern)
' The following is an alternative way of retrieving the Name property.
itemName = CStr(elementListItem.GetCachedPropertyValue(AutomationElement.NameProperty))
' This is yet another way, which returns AutomationElement.NotSupported if the element does
' not supply a value. If the second parameter is false, a default name is returned.
Dim objName As Object = elementListItem.GetCachedPropertyValue(AutomationElement.NameProperty, True)
If objName Is AutomationElement.NotSupported Then
itemName = "Unknown"
Else
itemName = CStr(objName)
End If
' The following call raises an exception, because only the cached properties are available,
' as specified by cacheRequest.AutomationElementMode. If AutomationElementMode had its
' default value (Full), this call would be valid.
'** bool enabled = elementListItem.Current.IsEnabled; **
End Sub