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