简化select case语句以避免DRY

Question

如何重构这段代码以避免重复?特别是如果有更多的病例!我读过关于用字典简化选择情况的文章，但我不知道如何在这种情况下使用它。有什么建议吗?

    Dim sPath As String = String.Empty
    Dim aThing As Decimal
    Select Case True
        Case (aThing < 7.5)
            sPath = "~/images/Grafik_7.5.png"
        Case (aThing >= 7.5 AndAlso aThing < 8.75)
            sPath = "~/images/Grafik_18.75.png"
        Case (aThing >= 58.75 AndAlso aThing < 60)
            sPath = "~/images/Grafik_60.png"
        Case (aThing >= 60 AndAlso aThing < 61.25)
            sPath = "~/images/Grafik_61.25.png"
        Case (aThing >= 61.25 AndAlso aThing < 62.5)
            sPath = "~/images/Grafik_62.5.png"
        Case (aThing >= 62.5 AndAlso aThing < 63.75)
            sPath = "~/images/Grafik_63.75.png"
        Case (aThing >= 63.75 AndAlso aThing < 65)
            sPath = "~/images/Grafik_65.png"
        Case (aThing >= 65 AndAlso aThing < 66.25)
            sPath = "~/images/Grafik_66.25.png"
        Case (aThing >= 66.25)
            sPath = "~/images/Grafik_67.5.png"
    End Select

Answer 1

使用字典，您可以这样做:

Dim conditions = new Dictionary(of Predicate(of Double), String) From
{
    {Function(a) a < 7.5, "Grafik_7.5.png"},
    {Function(a) a >= 7.5 AndAlso a <= 8.75, "Grafik_8.75.png"},
    {Function(a) a >= 58.75 AndAlso a < 60, "Grafik_60.png"} 
}
Dim aThing = 8.3
Dim result = conditions.Single(Function (c) c.Key(aThing)).Value

但是请注意字典是没有排序的，所以要确保只有一个函数对任何给定的值返回True。

另一种方法是动态创建文件名，像这样:

Dim sizes = new List(Of Double) From {7.5, 8.75, 60, 61.25} 
Dim InvC = System.Globalization.CultureInfo.InvariantCulture
DIm size = sizes.First(Function(s) s > aThing).ToString(InvC)
Dim result = "Grafik_" + size + ".png"

Answer 2

这可能需要稍微改变，这取决于最大数值可以是什么，但我在想这样的东西:

    Dim values = {7.5D, 18.75D, 60D, 61.25D} 'etc.
    Dim value = values.First(Function(x) x > aThing)
    sPath = $"~images/Grafik_{value}.png