Question

对于我的课程项目，我必须创建成绩簿并编写LINQ语句以列出所有学生，按升序显示，并显示通过测试的每个人。我的所有陈述都返回了相同的信息，但情况并非如此。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，并更改显示（gradeBooks，＆＃34; Ascending Order＆＃34;）以显示（升序，＆＃34;升序＆＃34;）。

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

Answer 2

对于按分数订购的订单，您需要按分数请求订购

Dim ordered =
    From value In gradeBooks
    Order By value.Score
    Select value
display(ordered, "Ascending Order")

（我还更改了IEnumerable的名称以避免与关键字Ascending混淆）

在提取传递的可枚举

时也需要进行相同的更改

Dim passed =
    From gradeBook In gradeBooks
    Where gradeBook.Score > 60
    Order By gradeBook.Score
    Select gradeBook
display(passed, "Students who passed: ")

您的实际代码是将整个成绩单作为对象传递给。通过这种方式，您需要实现（如在其他答案中所解释的）IEnumerable接口，以教授编译器如何将成绩单与另一个成绩簿进行比较以对其进行排序。但这可能不是真的需要在这里，只需将字段（数字或字符串）传递给订单就足够了

Answer 3

您重复看到相同信息的原因是您在同一个集合上调用了两次显示。一旦纠正，你应该抛出一个异常，因为你试图整个对象而不是对象的属性/字段。

VB.net中的LINQ语句

3 个答案: