Question

I have a UserControl class in a Windows Application project. One of the properties of it is a collection of another class that I have defined. I can’t seem to find a good example of how to get the standard collection editor working for it at design time.

I got it working using some example code I found to a degree, but the data in my collection doesn’t get saved. When I exit the form and open it back up in design time the data isn’t there any more.

Here is my class:

Public Class Gauge
Inherits Control

Private WithEvents _Captions As New CaptionCollection

<Category("Gauge"), _
TypeConverter(GetType(CaptionCollectionConverter)), _
Description("Custom text displayed on the gauge.")> _
Public Property Captions() As CaptionCollection
    Get
        Return _Captions
    End Get
    Set(ByVal value As CaptionCollection)
        _Captions = value
    End Set
End Property

<Category("Gauge"), _
TypeConverter(GetType(CaptionConverter)), _
Description("Custom text displayed on the gauge.")> _
Public Class Caption
    Private _Text As String = ""
    Private _Color As Color = Color.Black
    Private _TextIsValue As Boolean
    Private _Position As New Point(0, 0)

    Public Property Text() As String
        Get
            Return _Text
        End Get
        Set(ByVal value As String)
            If _Text <> value Then
                _Text = value
            End If
        End Set
    End Property

    Public Property Color() As Color
        Get
            Return _Color
        End Get
        Set(ByVal value As Color)
            If _Color <> value Then
                _Color = value
            End If
        End Set
    End Property

    Public Property TextIsValue() As Boolean
        Get
            Return _TextIsValue
        End Get
        Set(ByVal value As Boolean)
            If _TextIsValue <> value Then
                _TextIsValue = value
            End If
        End Set
    End Property

    Public Property Position() As Point
        Get
            Return _Position
        End Get
        Set(ByVal value As Point)
            If _Position <> value Then
                _Position = value
            End If
        End Set
    End Property
End Class

Public Class CaptionCollection
    Inherits CollectionBase
    Implements ICustomTypeDescriptor

    Public Sub Add(ByVal c As Caption)
        Me.List.Add(c)
    End Sub

    Public Sub Remove(ByVal c As Caption)
        Me.List.Remove(c)
    End Sub

    Default Public ReadOnly Property Item(ByVal index As Integer) As Caption
        Get
            Return DirectCast(Me.List(index), Caption)
        End Get
    End Property

    ' Implementation of interface ICustomTypeDescriptor 
    Public Function GetClassName() As String Implements System.ComponentModel.ICustomTypeDescriptor.GetClassName
        Return TypeDescriptor.GetClassName(Me, True)
    End Function

    Public Function GetAttributes() As AttributeCollection Implements System.ComponentModel.ICustomTypeDescriptor.GetAttributes
        Return TypeDescriptor.GetAttributes(Me, True)
    End Function

    Public Function GetComponentName() As String Implements System.ComponentModel.ICustomTypeDescriptor.GetComponentName
        Return TypeDescriptor.GetComponentName(Me, True)
    End Function

    Public Function GetConverter() As TypeConverter Implements System.ComponentModel.ICustomTypeDescriptor.GetConverter
        Return TypeDescriptor.GetConverter(Me, True)
    End Function

    Public Function GetDefaultEvent() As EventDescriptor Implements System.ComponentModel.ICustomTypeDescriptor.GetDefaultEvent
        Return TypeDescriptor.GetDefaultEvent(Me, True)
    End Function

    Public Function GetDefaultProperty() As PropertyDescriptor Implements System.ComponentModel.ICustomTypeDescriptor.GetDefaultProperty
        Return TypeDescriptor.GetDefaultProperty(Me, True)
    End Function

    Public Function GetEditor(ByVal editorBaseType As Type) As Object Implements System.ComponentModel.ICustomTypeDescriptor.GetEditor
        Return TypeDescriptor.GetEditor(Me, editorBaseType, True)
    End Function

    Public Function GetEvents(ByVal attributes As Attribute()) As EventDescriptorCollection Implements System.ComponentModel.ICustomTypeDescriptor.GetEvents
        Return TypeDescriptor.GetEvents(Me, attributes, True)
    End Function

    Public Function GetEvents() As EventDescriptorCollection Implements System.ComponentModel.ICustomTypeDescriptor.GetEvents
        Return TypeDescriptor.GetEvents(Me, True)
    End Function

    Public Function GetPropertyOwner(ByVal pd As PropertyDescriptor) As Object Implements System.ComponentModel.ICustomTypeDescriptor.GetPropertyOwner
        Return Me
    End Function

    Public Function GetProperties(ByVal attributes As Attribute()) As PropertyDescriptorCollection Implements System.ComponentModel.ICustomTypeDescriptor.GetProperties
        Return GetProperties()
    End Function

    Public Function GetProperties() As PropertyDescriptorCollection Implements System.ComponentModel.ICustomTypeDescriptor.GetProperties
        ' Create a collection object to hold property descriptors
        Dim pds As New PropertyDescriptorCollection(Nothing)

        ' Iterate the list of employees
        For i As Integer = 0 To Me.List.Count - 1
            ' Create a property descriptor for the caption item and add to the property descriptor collection
            Dim pd As New CaptionCollectionPropertyDescriptor(Me, i)
            pds.Add(pd)
        Next
        ' return the property descriptor collection
        Return pds
    End Function
End Class

' This is a special type converter which will be associated with the Caption class.
' It converts a Caption object to string representation for use in a property grid.
Friend Class CaptionConverter
    Inherits ExpandableObjectConverter

    Public Overloads Overrides Function ConvertTo(ByVal context As ITypeDescriptorContext, ByVal culture As System.Globalization.CultureInfo, ByVal value As Object, ByVal destType As Type) As Object
        'Return "(Collection)"
        If destType Is GetType(String) AndAlso TypeOf value Is Caption Then
            ' Cast the value to an Caption type
            Dim emp As Caption = DirectCast(value, Caption)
            ' Return the text for display.
            Return emp.Text
        End If
        Return MyBase.ConvertTo(context, culture, value, destType)
    End Function
End Class

' This is a special type converter which will be associated with the CaptionCollection class.
' It converts a CaptionCollection object to a string representation for use in a property grid.
Friend Class CaptionCollectionConverter
    Inherits ExpandableObjectConverter

    Public Overloads Overrides Function ConvertTo(ByVal context As ITypeDescriptorContext, ByVal culture As System.Globalization.CultureInfo, ByVal value As Object, ByVal destType As Type) As Object
        If destType Is GetType(String) AndAlso TypeOf value Is CaptionCollection Then
            ' Return department and department role separated by comma.
            Return "(Collection)"
        End If
        Return MyBase.ConvertTo(context, culture, value, destType)
    End Function
End Class

Public Class CaptionCollectionPropertyDescriptor
    Inherits PropertyDescriptor
    Private collection As CaptionCollection = Nothing
    Private index As Integer = -1

    Public Sub New(ByVal coll As CaptionCollection, ByVal idx As Integer)
        MyBase.New("#" & idx.ToString(), Nothing)
        Me.collection = coll
        Me.index = idx
    End Sub

    Public Overloads Overrides ReadOnly Property Attributes() As AttributeCollection
        Get
            Return New AttributeCollection(Nothing)
        End Get
    End Property

    Public Overloads Overrides Function CanResetValue(ByVal component As Object) As Boolean
        Return True
    End Function

    Public Overloads Overrides ReadOnly Property ComponentType() As Type
        Get
            Return Me.collection.[GetType]()
        End Get
    End Property

    Public Overloads Overrides ReadOnly Property DisplayName() As String
        Get
            Return "Caption" + (index + 1).ToString()
        End Get
    End Property

    Public Overloads Overrides ReadOnly Property Description() As String
        Get
            Return "Caption" + (index + 1).ToString()
        End Get
    End Property

    Public Overloads Overrides Function GetValue(ByVal component As Object) As Object
        Return Me.collection(index)
    End Function

    Public Overloads Overrides ReadOnly Property IsReadOnly() As Boolean
        Get
            Return False
        End Get
    End Property

    Public Overloads Overrides ReadOnly Property Name() As String
        Get
            Return "#" & index.ToString()
        End Get
    End Property

    Public Overloads Overrides ReadOnly Property PropertyType() As Type
        Get
            Return Me.collection(index).[GetType]()
        End Get
    End Property

    Public Overloads Overrides Sub ResetValue(ByVal component As Object)
    End Sub

    Public Overloads Overrides Function ShouldSerializeValue(ByVal component As Object) As Boolean
        Return True
    End Function

    Public Overloads Overrides Sub SetValue(ByVal component As Object, ByVal value As Object)
        ' this.collection[index] = value;
    End Sub
End Class

End Class

Answer 1

I found my answer. The thing I was missing was this attribute in the Captions property: DesignerSerializationVisibility(DesignerSerializationVisibility.Content