WP7中的扩展

Question

Imports System.Runtime.CompilerServices

Public Module ColorExtension
    <Extension()> _
    Public Function ToColor(ByVal argb As UInteger) As Global.System.Windows.Media.Color
        Return Global.System.Windows.Media.Color.FromArgb(CByte((argb And -16777216) >> &H18), CByte((argb And &HFF0000) >> &H10), CByte((argb And &HFF00) >> 8), CByte(argb And &HFF))
    End Function
End Module



Public Class Test
    Private Sub TestExt()
        Dim Col As System.Windows.Media.Color
        Col = System.Windows.Media.Color.ToColor(100)'<-- Error
        Col.ToColor(100)'<-- Error
    End Sub
End Class

When I use this code, I got this exception Error 1 'ToColor' is not a member of 'System.Windows.Media.Color'. C:...\\ColorExtension.vb

Please any advice how to develop Extension functions like this Color extension one.

Answer 1

1. Extension methods can be fired on object of class, not the class itself.
2. Your extension method is set on UInteger class, not on Color . Type you extends is the type of first method parameter.
3. You cannot add new method to a class that could be fired like you tried to do it.

You can use your extension method in two ways:

1. Standard method invocation: ColorExtension.ToColor(100)
2. Using the extension method syntax: 100.ToColor()