System.Predicate 通用类 vb.net c#

Wrapper class for a Predicate(Of T)  (C#版本)

public delegate bool PredicateWrapperDelegate<T, A>(T item, A argument);
    public class PredicateWrapper<T, A>
    {
        private A _argument;
        private PredicateWrapperDelegate<T, A> _wrapperDelegate;

        public PredicateWrapper(A argument, PredicateWrapperDelegate<T, A> wrapperDelegate)
        {
            _argument = argument;
            _wrapperDelegate = wrapperDelegate;
        }

        private bool InnerPredicate(T item)
        {
            return _wrapperDelegate(item, _argument);
        }
        public static implicit operator Predicate<T>(PredicateWrapper<T, A> wrapper)
        {
            return new Predicate<T>(wrapper.InnerPredicate);
        }

}
Wrapper class for a Predicate(Of T)  (vb.net版本)


Code:


 

Public Delegate Function PredicateWrapperDelegate(Of T, A) _
 (ByVal item As T, ByVal argument As A) As Boolean

Public Class PredicateWrapper(Of T, A)

    Private _argument As A
    Private _wrapperDelegate As PredicateWrapperDelegate(Of T, A)

    Public Sub New(ByVal argument As A, _
     ByVal wrapperDelegate As PredicateWrapperDelegate(Of T, A))

        _argument = argument
        _wrapperDelegate = wrapperDelegate
    End Sub

    Private Function InnerPredicate(ByVal item As T) As Boolean
        Return _wrapperDelegate(item, _argument)
    End Function

    Public Shared Widening Operator CType( _
     ByVal wrapper As PredicateWrapper(Of T, A)) _
     As Predicate(Of T)

        Return New Predicate(Of T)(AddressOf wrapper.InnerPredicate)
    End Operator

End Class

 

Generic user class I used for testing.


Code:


 

Public Class User

    Public Sub New(ByVal firstName As String, ByVal lastName As String)
        Me._firstName = firstName
        Me._lastName = lastName
    End Sub

    Private _firstName As String
    Public Property firstName() As String
        Get
            Return _firstName
        End Get
        Set(ByVal value As String)
            _firstName = value
        End Set
    End Property


    Private _lastName As String
    Public Property lastName() As String
        Get
            Return _lastName
        End Get
        Set(ByVal value As String)
            _lastName = value
        End Set
    End Property

End Class

Example usage where I pass a search parameter 'Jim' in for the first name.


Code:


Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim userList As New List(Of User) _
         (New User() {New User("Jim", "Smith"), New User("John", "Doe"), New User("Bill", "Jones")})
        Dim searchedUser As User = _
         userList.Find(New PredicateWrapper(Of User, String)("Jim", AddressOf FirstNameMatch))
    End Sub

    Private Function FirstNameMatch(ByVal item As User, ByVal searchArg As String) As Boolean
        Return item.firstName.Equals(searchArg)
    End Function

End Class