为什么FxCop会给我一个"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正在给我这个警告:

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)
}

我究竟做错了什么？我检查类型,如果它是相同的,则抛出.

Answer 1

因为你可以重写你的演员阵容

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

比的组合更好的性能 is和DirectCast