Question

我有这堂课：

Public Class AdDimensionsToAdDetails
    Public Sub New()
    End Sub

    Public Overrides Function equals(adDimensions As AdDimensions) As Boolean
        If adDimensions Is Nothing Then
            Return False
        End If

        Return Me.adDimensionsToAdDetails.Keys.First().width = adDimensions.width AndAlso
            Me.adDimensionsToAdDetails.Keys.First().height = adDimensions.height

    End Function

    Public ReadOnly Property adDimensionsToAdDetails As Dictionary(Of AdDimensions, AdDetails)
        Get
            Return New Dictionary(Of AdDimensions, AdDetails) From {
                {New AdDimensions(300, 250), New AdDetails(New MinMaxJobsCount(3, 3), True)},
                {New AdDimensions(300, 50), New AdDetails(New MinMaxJobsCount(1, 1), False)},
                {New AdDimensions(728, 90), New AdDetails(New MinMaxJobsCount(3, 3), True)},
                {New AdDimensions(160, 600), New AdDetails(New MinMaxJobsCount(3, 7), True)}
            }

        End Get
    End Property

End Class

我想检查adDimensionsToAdDetails是否包含300,250的密钥。

所以我尝试过：

dim adDimensions as new AdDimensions(300,250)

' it contains the key
if (AdDimensionsToAdDetails.adDimensionsToAdDetails.ContainsKey(adDimensions)) then

End If

我读到我需要覆盖equals。

所以我尝试了，但我得到了： function 'equals' cannot be declared 'overrides' because it does not override a function in a base class

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Answer 1

Dictionary类实现为哈希表。在比较键值时，Dictionary将在有问题的关键项上调用GetHashCode方法，并且只有当它具有该特定哈希码的条目时才会调用项目Equals Dictionary(Of AdDimensions, AdDetails).ContainsKey 1}}验证相等的方法。

因此，要使用Equals方法，您需要覆盖AdDimensions类继承自GetHashCode的{{1}}和System.Object方法。

以下是一种可能的实现，基于您的代码。

Class AdDimensions
    Public Sub New(height As Int32, width As Int32)
        Me.height = height
        Me.width = width
    End Sub
    Public height As Int32
    Public width As Int32

    Public Overrides Function Equals(obj As Object) As Boolean
        Dim other As AdDimensions = TryCast(obj, AdDimensions)
        Dim ret As Boolean
        If other IsNot Nothing Then
            ret = (Me.width = other.width) AndAlso (Me.height = other.height)
        End If
        Return ret
    End Function

    Public Overrides Function GetHashCode() As Integer
        Return Me.width Xor Me.height
    End Function
End Class

Answer 2

您无法更改要覆盖的方法的签名。 Object.Equals方法有一个Object类型的参数。您的覆盖必须具有相同的内容。

那就是说，我刚刚意识到你在错误的班级里有这种方法。如果意图是比较该类型的两个实例，则需要在AdDimensions类中。

当key是一个对象时，实现containsKey

2 个答案: