SankeyLayoutAlgorithmBase Class

<dxsa:SankeyDiagramControl x:Name="sankeyDiagramControl1" DataSource="{Binding Data}" 
                            SourceDataMember="Source" 
                            TargetDataMember="Target" 
                            WeightDataMember="Value">
    <dxsa:SankeyDiagramControl.DataContext>
        <local:SankeyViewModel/>
    </dxsa:SankeyDiagramControl.DataContext>
    <dxsa:SankeyDiagramControl.LayoutAlgorithm>
        <local:MyLayoutAlgorithm/>
    </dxsa:SankeyDiagramControl.LayoutAlgorithm>
</dxsa:SankeyDiagramControl>

public class SankeyViewModel {
    public List<SankeyItem> Data {
        get { return GetData(); }
    }
    public List<SankeyItem> GetData() {
        List<SankeyItem> data = new List<SankeyItem>{
            new SankeyItem { Source = "France", Target = "UK", Value = 53 },
            new SankeyItem { Source = "Australia", Target = "UK", Value = 72 },
            new SankeyItem { Source = "France", Target = "Canada", Value = 81 },
            new SankeyItem { Source = "China", Target = "Canada", Value = 96 },
            new SankeyItem { Source = "UK", Target = "France", Value = 61 },
            new SankeyItem { Source = "Canada", Target = "France", Value = 89 }
        };
        return data;
    }
}
public class SankeyItem {
    public string Source { get; set; }
    public string Target { get; set; }
    public double Value { get; set; }
}
public class MyLayoutAlgorithm : SankeyLayoutAlgorithmBase {
    void SpreadLevelIndex(ISankeyNodeLayoutItem node, int startingLevelIndex = 0) {
        node.LevelIndex = startingLevelIndex;
        if (node.OutputLinks == null)
            return;
        foreach (var outputLink in node.OutputLinks)
            SpreadLevelIndex(outputLink.Target, startingLevelIndex + 1);
    }
    protected override ChartDependencyObject CreateObject() => new MyLayoutAlgorithm();
    public override void CalculateNodeBounds(IEnumerable<ISankeyNodeLayoutItem> nodes, System.Drawing.Rectangle bounds) {
        foreach (var node in nodes)
            if (node.InputLinks == null || node.InputLinks.Count == 0)
                SpreadLevelIndex(node);
        int nodeWidth = bounds.Width / 10;
        int nodeHeight = bounds.Height / 10;
        int levelCount = nodes.Max(node => node.LevelIndex) + 1;
        int spaceBetweenLevels = (bounds.Width - nodeWidth) / (levelCount - 1);
        int maxNodeCountInALevel = nodes.GroupBy(node => node.LevelIndex).Max(group => group.Count());
        int spaceBetweenNodes = (bounds.Height - nodeHeight) / (maxNodeCountInALevel - 1);
        Dictionary<int, int> levelNodeCountPairs = new Dictionary<int, int>();
        foreach (var node in nodes) {
            if (!levelNodeCountPairs.TryGetValue(node.LevelIndex, out int nodeCount))
                levelNodeCountPairs.Add(node.LevelIndex, 0);
            levelNodeCountPairs[node.LevelIndex]++;
            node.Bounds = new System.Drawing.Rectangle(bounds.Left + node.LevelIndex * spaceBetweenLevels, bounds.Top + nodeCount * spaceBetweenNodes, nodeWidth, nodeHeight);
        }
    }
}

Public Class SankeyViewModel
    Public ReadOnly Property Data As List(Of SankeyItem)
        Get
            Return GetData()
        End Get
    End Property

    Public Function GetData() As List(Of SankeyItem)
        Dim data As List(Of SankeyItem) = New List(Of SankeyItem) From {
            New SankeyItem With {
                .Source = "France",
                .Target = "UK",
                .Value = 53
            },
            New SankeyItem With {
                .Source = "Australia",
                .Target = "UK",
                .Value = 72
            },
            New SankeyItem With {
                .Source = "France",
                .Target = "Canada",
                .Value = 81
            },
            New SankeyItem With {
                .Source = "China",
                .Target = "Canada",
                .Value = 96
            },
            New SankeyItem With {
                .Source = "UK",
                .Target = "France",
                .Value = 61
            },
            New SankeyItem With {
                .Source = "Canada",
                .Target = "France",
                .Value = 89
            }
        }
        Return data
    End Function
End Class

Public Class SankeyItem
    Public Property Source As String
    Public Property Target As String
    Public Property Value As Double
End Class

Public Class MyLayoutAlgorithm
    Inherits SankeyLayoutAlgorithmBase

    Private Sub SpreadLevelIndex(ByVal node As ISankeyNodeLayoutItem, ByVal Optional startingLevelIndex As Integer = 0)
        node.LevelIndex = startingLevelIndex
        If node.OutputLinks Is Nothing Then Return

        For Each outputLink In node.OutputLinks
            SpreadLevelIndex(outputLink.Target, startingLevelIndex + 1)
        Next
    End Sub

    Protected Overrides Function CreateObject() As ChartDependencyObject
        Return New MyLayoutAlgorithm()
    End Function

    Public Overrides Sub CalculateNodeBounds(ByVal nodes As IEnumerable(Of ISankeyNodeLayoutItem), ByVal bounds As Drawing.Rectangle)
        For Each node In nodes
            If node.InputLinks Is Nothing OrElse node.InputLinks.Count = 0 Then SpreadLevelIndex(node)
        Next

        Dim nodeWidth As Integer = bounds.Width / 10
        Dim nodeHeight As Integer = bounds.Height / 10
        Dim levelCount As Integer = nodes.Max(Function(node) node.LevelIndex) + 1
        Dim spaceBetweenLevels As Integer = (bounds.Width - nodeWidth) / (levelCount - 1)
        Dim maxNodeCountInALevel As Integer = nodes.GroupBy(Function(node) node.LevelIndex).Max(Function(group) group.Count())
        Dim spaceBetweenNodes As Integer = (bounds.Height - nodeHeight) / (maxNodeCountInALevel - 1)
        Dim levelNodeCountPairs As Dictionary(Of Integer, Integer) = New Dictionary(Of Integer, Integer)()
        Dim nodeCount As Integer = Nothing

        For Each node In nodes
            If Not levelNodeCountPairs.TryGetValue(node.LevelIndex, nodeCount) Then levelNodeCountPairs.Add(node.LevelIndex, 0)
            levelNodeCountPairs(node.LevelIndex) += 1
            node.Bounds = New Drawing.Rectangle(bounds.Left + node.LevelIndex * spaceBetweenLevels, bounds.Top + nodeCount * spaceBetweenNodes, nodeWidth, nodeHeight)
        Next
    End Sub
End Class