VB.NET中，如何根据值x、y、z在List(Of T)中精确查找特定项目？

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我有以下设置：plaintextClass Aproperty x as stringproperty y as intproperty z as StringEnd Class

Class CollOfAinherits List(Of A)End Class我想得到的是集合中的Item属性，我可以这样表示：plaintextdim c as new CollOfA.item(this, 2, that)

我有以下设置：

Class A property x as string property y as int property z as String End Class Class CollOfA inherits List(Of A) End Class

我想要的是集合中的Item属性,我可以说：

dim c as new CollOfA c.item("this", 2, "that")

我试过在CollOfA中实现以下内容：

Class CollOfA inherits List(Of A) Default Public Overridable Shadows ReadOnly Property Item(ByVal x As String, ByVal y As Integer, byval z as string) Get ' I want to do something like: ' ForEach item in me see if anything matches these three things End Get End Property End Class

我知道谓词,但我正在努力设置谓词的标准(即传递x,y和z).

有没有人实现类似的东西？

以下是我提出的两种完成问题的方法.一种方法是使用LINQ查询语法进行过滤;第二个使用自定义对象来保存谓词参数,然后使用该对象来执行过滤器.

在Item属性中使用LINQ语法：

Default Public Overridable Shadows ReadOnly Property Item(ByVal x As String, ByVal y As Integer, ByVal z As String) As IEnumerable(Of A) Get Return (From theA In Me Where (theA.x = x And theA.y = y And theA.z = z) Select theA) End Get End Property

另一种方法是创建一个PredicateParameter类来保存您的参数,以及一个用于执行过滤器的委托方法.我在MSDN评论中看到了这一点 – 这是link.这是课程：

Class PredicateParams Public Sub New(ByVal theA As A) Criteria = theA End Sub Public Property Criteria As A Public Function IsMatch(ByVal theA As A) As Boolean Return (theA.x = Criteria.x And theA.y = Criteria.y And theA.z = Criteria.z) End Function End Class

这是使用它的CollOfA类中的属性：

Public Overridable Shadows ReadOnly Property ItemPred(ByVal x As String, ByVal y As Integer, ByVal z As String) As IEnumerable(Of A) Get Dim predA As New A predA.x = x predA.y = y predA.z = z Dim pred As New PredicateParams(predA) Return Me.FindAll(AddressOf pred.IsMatch) End Get End Property

最后,这是一个测试它的控制台运行器.

Sub Main() Dim mycoll As New CollOfA() For index = 1 To 100 Dim anA As New A() anA.x = (index Mod 2).ToString() anA.y = index Mod 4 anA.z = (index Mod 3).ToString() mycoll.Add(anA) Next Dim matched As IEnumerable(Of A) = mycoll.Item("1", 3, "2") Dim matched2 As IEnumerable(Of A) = mycoll.ItemPred("1", 3, "2") Console.WriteLine(matched.Count.ToString()) 'output from first search Console.WriteLine(matched2.Count.ToString()) 'output from second search (s/b same) Console.ReadLine() End Sub

希望这会有所帮助.可能有更优雅的方式来做到这一点,但我没有看到一个. (顺便说一句,我通常使用C#,所以我的VB.NET有点生锈.)