在列舉中找到最接近的值

下一個程式碼說明了如何找到最接近的列舉值。

首先，我們定義此 Enum ，用於指定搜尋條件（搜尋方向）

Public Enum EnumFindDirection As Integer
    Nearest = 0
    Less = 1
    LessOrEqual = 2
    Greater = 3
    GreaterOrEqual = 4
End Enum

現在我們實現搜尋演算法：

<DebuggerStepThrough>
Public Shared Function FindNearestEnumValue(Of T)(ByVal value As Long,
                                                  ByVal direction As EnumFindDirection) As T

    Select Case direction

        Case EnumFindDirection.Nearest
            Return (From enumValue As T In [Enum].GetValues(GetType(T)).Cast(Of T)()
                    Order By Math.Abs(value - Convert.ToInt64(enumValue))
                    ).FirstOrDefault

        Case EnumFindDirection.Less
            If value < Convert.ToInt64([Enum].GetValues(GetType(T)).Cast(Of T).First) Then
                Return [Enum].GetValues(GetType(T)).Cast(Of T).FirstOrDefault

            Else
                Return (From enumValue As T In [Enum].GetValues(GetType(T)).Cast(Of T)()
                        Where Convert.ToInt64(enumValue) < value
                        ).LastOrDefault
            End If

        Case EnumFindDirection.LessOrEqual
            If value < Convert.ToInt64([Enum].GetValues(GetType(T)).Cast(Of T).First) Then
                Return [Enum].GetValues(GetType(T)).Cast(Of T).FirstOrDefault

            Else
                Return (From enumValue As T In [Enum].GetValues(GetType(T)).Cast(Of T)()
                        Where Convert.ToInt64(enumValue) <= value
                        ).LastOrDefault
            End If

        Case EnumFindDirection.Greater
            If value > Convert.ToInt64([Enum].GetValues(GetType(T)).Cast(Of T).Last) Then
                Return [Enum].GetValues(GetType(T)).Cast(Of T).LastOrDefault

            Else
                Return (From enumValue As T In [Enum].GetValues(GetType(T)).Cast(Of T)()
                        Where Convert.ToInt64(enumValue) > value
                        ).FirstOrDefault
            End If

        Case EnumFindDirection.GreaterOrEqual
            If value > Convert.ToInt64([Enum].GetValues(GetType(T)).Cast(Of T).Last) Then
                Return [Enum].GetValues(GetType(T)).Cast(Of T).LastOrDefault

            Else
                Return (From enumValue As T In [Enum].GetValues(GetType(T)).Cast(Of T)()
                        Where Convert.ToInt64(enumValue) >= value
                        ).FirstOrDefault
            End If

    End Select

End Function

用法示例：

Public Enum Bitrate As Integer
    Kbps128 = 128
    Kbps192 = 192
    Kbps256 = 256
    Kbps320 = 320
End Enum

Dim nearestValue As Bitrate = FindNearestEnumValue(Of Bitrate)(224, EnumFindDirection.GreaterOrEqual)