Question

I am using a PropertyGrid control to edit my class properties and I am trying to set certain properties read-only depending on other property settings.

This is the code of my class:

Imports System.ComponentModel
Imports System.Reflection

Public Class PropertyClass

    Private _someProperty As Boolean = False

    <DefaultValue(False)>
    Public Property SomeProperty As Boolean
        Get
            Return _someProperty
        End Get
        Set(value As Boolean)
            _someProperty = value
            If value Then
                SetReadOnlyProperty("SerialPortNum", True)
                SetReadOnlyProperty("IPAddress", False)
            Else
                SetReadOnlyProperty("SerialPortNum", False)
                SetReadOnlyProperty("IPAddress", True)
            End If
        End Set
    End Property

    Public Property IPAddress As String = "0.0.0.0"

    Public Property SerialPortNum As Integer = 0

    Private Sub SetReadOnlyProperty(ByVal propertyName As String, ByVal readOnlyValue As Boolean)
        Dim descriptor As PropertyDescriptor = TypeDescriptor.GetProperties(Me.GetType)(propertyName)
        Dim attrib As ReadOnlyAttribute = CType(descriptor.Attributes(GetType(ReadOnlyAttribute)), ReadOnlyAttribute)
        Dim isReadOnly As FieldInfo = attrib.GetType.GetField("isReadOnly", (BindingFlags.NonPublic Or BindingFlags.Instance))
        isReadOnly.SetValue(attrib, readOnlyValue)
    End Sub
End Class

This is the code I am using to edit the values:

    Dim c As New PropertyClass
    PropertyGrid1.SelectedObject = c

The problem is that when I set SomeProperty to True, nothing happens and when I then set it to False again it sets all properties Read-Only. Can someone see an error in my code?

Answer 1

Try decorating ALL of your class properties with the ReadOnly attribute:

<[ReadOnly](False)> _
Public Property SomeProperty As Boolean
  Get
    Return _someProperty
  End Get
  Set(value As Boolean)
    _someProperty = value
    If value Then
      SetReadOnlyProperty("SerialPortNum", True)
      SetReadOnlyProperty("IPAddress", False)
    Else
      SetReadOnlyProperty("SerialPortNum", False)
      SetReadOnlyProperty("IPAddress", True)
    End If
  End Set
End Property

<[ReadOnly](False)> _
Public Property IPAddress As String = "0.0.0.0"

<[ReadOnly](False)> _
Public Property SerialPortNum As Integer = 0

Found it from this Code Project: Enabling/disabling properties at runtime in the PropertyGrid

In order for all this to work properly, it is important to statically define the ReadOnly attribute of every property of the class to whatever value you want. If not, changing the attribute at runtime that way will wrongly modify the attributes of every property of the class.