Disabling items in PropertyGrid using Custom Attributes

问题

I am able to selectively enable / disable items in a PropertyGrid by setting BrowsableAttributes to an array containing CategoryAttribute objects. However, I wish to enable some items within a category and disable others within the same category, so I thought I would create my own custom attribute class and apply this to the properties in my object, but this does not seem to work.

Here is my custom attribute class:

Public Enum HeadType
    DMA = 1
    TMA = 2
    Both = 0
End Enum
<AttributeUsage(AttributeTargets.Property)>
Public Class HeadTypeAttribute
    Inherits Attribute
    Public Property HeadType As HeadType
    Public Sub New(HeadType As HeadType)
        Me.HeadType = HeadType
    End Sub
    Public Overrides Function Match(obj As Object) As Boolean
        Debug.Print("HeadTypeAttribute.Match obj.HeadType=" & obj.HeadType.ToString())
        Debug.Print("HeadTypeAttribute.Match Me.HeadType=" & Me.HeadType.ToString())
        Dim bMatch As Boolean = TypeOf obj Is HeadTypeAttribute AndAlso CType(obj, HeadTypeAttribute).HeadType = Me.HeadType
        Debug.Print(bMatch)
        Return bMatch
    End Function
End Class

I set BrowsableAttibutes to an array containing two instances of my HeadTypeAttribute class, one with HeadType = HeadType.Both and one set to either HeadType.DMA or HeadType.TMA. I can see that the Match method is being called and is returning true for some items, but the grid is always empty.

回答1:

Not adding the Both item in BrowsableAttributes and changing the Match function to always return True when the Both value is encountered seems to fix it:

Public Overrides Function Match(obj As Object) As Boolean
    Return TypeOf obj Is HeadTypeAttribute AndAlso (CType(obj, HeadTypeAttribute).HeadType = Me.HeadType OrElse CType(obj, HeadTypeAttribute).HeadType = HeadType.Both)
End Function

来源：https://stackoverflow.com/questions/28761295/disabling-items-in-propertygrid-using-custom-attributes