vb.net - VB.net 中的 LINQ 语句

Question

对于我的类(class)项目，我必须创建一个成绩簿并编写 LINQ 语句来列出所有学生，按升序显示，并显示通过测试的每个人。我所有的陈述都返回相同的信息，但事实并非如此。这是我的代码。

Public Class GradeBook
Private nameValue As String
Private scoreValue As Integer
Public Sub New(ByVal n As String, ByVal s As Integer)
    nameValue = n
    scoreValue = s
End Sub
Public Property Name() As String
    Get
        Return nameValue
    End Get
    Set(ByVal value As String)
        nameValue = value
    End Set
End Property

Public Property Score() As Integer
    Get
        Return scoreValue
    End Get
    Set(ByVal value As Integer)
        scoreValue = value
    End Set
End Property
Public Sub displayGradeBook()
    Console.WriteLine("Name: " & Name & vbTab & "Score: " & Score)
End Sub

End Class

 Sub Main()
    Dim g1 As New GradeBook("AAA", 70)
    Dim g2 As New GradeBook("BBB", 50)
    Dim g3 As New GradeBook("CCC", 100)
    Dim g4 As New GradeBook("DDD", 80)
    'add g1, g2, g3 and g4 in a array and display all student scores 
    Dim gradeBooks As GradeBook() = {g1, g2, g3, g4}
    display(gradeBooks, "Scores for all students: ")

    'create a LINQ which get all scores in ascending order and display them.
    Dim ascending =
        From value In gradeBooks
        Order By value Ascending
        Select value
    display(gradeBooks, "Ascending Order")


    'create a LINQ which get all students who passed the exam
    Dim passed =
        From gradeBook In gradeBooks
        Where gradeBook.Score > 60
        Order By gradeBook
        Select gradeBook
    display(passed, "Students who passed: ")



    'display number of passed students, their names and scores  




End Sub


'display gradeBook's information 
Private Sub display(ByVal gradeBooks As IEnumerable, ByVal header As String)
    Console.WriteLine(header)
    For Each g As GradeBook In gradeBooks
        g.displayGradeBook()
    Next
    Console.WriteLine()
    Console.ReadLine()

End Sub

End Module

Answer 1

实现Icomparable接口(interface)，将display(gradeBooks, "Ascending Order")改为display(ascending, "Ascending Order")。

这段代码对我有用。

Module Module1


    Public Class GradeBook
        Implements IComparable(Of GradeBook)

        Private nameValue As String
        Private scoreValue As Integer
        Public Sub New(ByVal n As String, ByVal s As Integer)
            nameValue = n
            scoreValue = s
        End Sub
        Public Property Name() As String
            Get
                Return nameValue
            End Get
            Set(ByVal value As String)
                nameValue = value
            End Set
        End Property

        Public Property Score() As Integer
            Get
                Return scoreValue
            End Get
            Set(ByVal value As Integer)
                scoreValue = value
            End Set
        End Property
        Public Sub displayGradeBook()
            Console.WriteLine("Name: " & Name & vbTab & "Score: " & Score)
        End Sub

        Public Function CompareTo(ByVal other As GradeBook) As Integer Implements System.IComparable(Of GradeBook).CompareTo
            '-1 = less than other; 0 = same as other; +1 = greater than other'
            If IsNothing(other) Then
                Return 1
            End If

            If Me.Score > other.Score Then
                Return 1
            End If

            If Me.Score < other.Score Then
                Return -1
            End If

            Return 0


        End Function

    End Class

    Sub Main()
        Dim g1 As New GradeBook("AAA", 70)
        Dim g2 As New GradeBook("BBB", 50)
        Dim g3 As New GradeBook("CCC", 100)
        Dim g4 As New GradeBook("DDD", 80)
        'add g1, g2, g3 and g4 in a array and display all student scores 
        Dim gradeBooks As GradeBook() = {g1, g2, g3, g4}
        display(gradeBooks, "Scores for all students: ")

        'create a LINQ which get all scores in ascending order and display them.
        Dim ascending =
            From value In gradeBooks
            Order By value Ascending
            Select value
        display(ascending, "Ascending Order")


        'create a LINQ which get all students who passed the exam
        Dim passed =
            From gradeBook In gradeBooks
            Where gradeBook.Score > 60
            Order By gradeBook
            Select gradeBook

        display(passed, "Students who passed: ")



        'display number of passed students, their names and scores  




    End Sub


    'display gradeBook's information 
    Private Sub display(ByVal gradeBooks As IEnumerable, ByVal header As String)
        Console.WriteLine(header)
        For Each g As GradeBook In gradeBooks
            g.displayGradeBook()
        Next
        Console.WriteLine()
        Console.ReadLine()

    End Sub

End Module