为什么 FxCop 给我一个 "DoNotCastUnnecessarily" 警告？

Question

我有以下内容：

Option Strict On
Public NotInheritable Class Root
    Public Overrides Function Equals(obj As Object) As Boolean
        If TypeOf obj Is Root Then
            Dim rt As Root = DirectCast(obj, Root)
            Return rt.container.Equals(Me.container) AndAlso
                rt.question.Equals(Me.question)
        End If
        Return False
    End Function
End Class

FxCop 给我这个警告：

Warning, Certainty 95, for DoNotCastUnnecessarily
{
    Target       : #Equals(System.Object)  (IntrospectionTargetMember)
    Location     : file:///C:/..../Root.vb<46>  (String)
    Resolution   : "'obj', a parameter, is cast to type 'Root' multiple 
                   times in method 'Root.Equals(Object)'. Cache the result 
                   of the 'as' operator or direct cast in order to eliminate 
                   the redundant castclass instruction."
    Help         : http://msdn2.microsoft.com/library/ms182271(VS.90).aspx  (String)
    Category     : Microsoft.Performance  (String)
    CheckId      : CA1800  (String)
    RuleFile     : Performance Rules  (String)
    Info         : "Avoid duplicate casts where possible, since there is 
                   a cost associated with them."
    Created      : 4/21/2015 8:45:17 PM  (DateTime)
    LastSeen     : 4/21/2015 8:55:16 PM  (DateTime)
    Status       : Active  (MessageStatus)
    Fix Category : NonBreaking  (FixCategories)
}

我做错了什么？我检查类型，如果相同则进行转换。

Answer 1

因为您可以将演员表重写为

Dim rt As String = TryCast(obj, Root)
If Not (rt is Nohting) Then

这比 is 和 DirectCast

的组合更高效

Answer 2

正在使用的语言似乎是为 C# 量身定制的，但它基本上要求您使用 TryCast 而不是 Is

    Dim rt As Root = TryCast(obj, Root)
    If Not (rt Is Nothing) Then
        ' code
    End If

原因是无论如何这在内部执行等同于 TryCast，所以工作是重复的。

为什么 FxCop 给我一个 "DoNotCastUnnecessarily" 警告？

Why is FxCop giving me a "DoNotCastUnnecessarily" warning?

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