Creating a custom ImageList class by extended image property

I would like to replace my existing ImageLists with custom imagelists.

Public Class clsImageList

    Public Images As New List(Of clsImageItem)

    Public Sub Add(ByVal uGUID As String, ByRef uImage As Image)

        Dim nItem As New clsImageItem(uImage, uGUID)

        Images.Add(nItem)

    End Sub
    Public Function Image(ByVal uIndex As Integer) As Image

        Return Images.Item(uIndex).Image

    End Function

End Class

Public Class clsImageItem

    Public ReadOnly Property [Image] As Image
    Private _sGUID As String

    Public Sub New(uImage As Image, uGUID As String)

        Image = uImage
        _sGUID = uGUID

    End Sub

End Class

I am trying to make my class compatible with the .NET ImageList so that I don't have to change much code.

            Using g As Graphics = Graphics.FromImage(SomeBitmap)
                g.DrawImage(il.Images(myIndex), 0, 0, 256, 256)
            End Using

The error I'm getting is "There are no overloads for this function.".

I do understand this error, it can't render my clsImageItem, but I wonder if I could perhaps extend the Graphics to accept my clsImageItem.

Do I have to replace

.il.Images(myIndex)

.il.Images(myIndex).Image

or is there a simpler / more convinient way?

Solution

You can use il.Images(myIndex).Image that refers to the Images list in il.

You can use il.Image(myIndex) that refers to the Image function in il.

I wonder if I could perhaps extend the Graphics to accept my clsImageItem?

Yes you can create an extension method that accepts your clsImageItem class.

Imports System.Drawing
Imports System.Runtime.CompilerServices

Module GraphicsExtensions
    <Extension()>
    Public Sub DrawImage(ByVal g As Graphics, c As clsImageItem, x As Integer, y As Integer , w As Integer, h As integer)
        g.DrawImage(c.Image, x, y, w, h)
    End Sub
End Module

Then to use this overload, import the module that holds the extension method and then you can write:

g.DrawImage(il.Images(myIndex), 0, 0, 256, 256)

More information about Extension Methods

Extension methods enable developers to add custom functionality to data types that are already defined without creating a new derived type. Extension methods make it possible to write a method that can be called as if it were an instance method of the existing type.