public class DashboardViewModelBase :
    ViewModelBase

Public Class DashboardViewModelBase
    Inherits ViewModelBase

//...
IDashboardControlProvider provider = (IDashboardControlProvider)values[1];
ChartDashboardItem chartItem = provider.Dashboard.Items[itemName] as ChartDashboardItem;
//...

'...
Dim provider As IDashboardControlProvider = CType(values(1), IDashboardControlProvider)
Dim chartItem As ChartDashboardItem = TryCast(provider.Dashboard.Items(itemName), ChartDashboardItem)
'...

<dxc:ChartControl Style="{Binding Path=(dxdash:DashboardLayoutItem.ViewStyle), RelativeSource={RelativeSource TemplatedParent}}">
//...
    <MultiBinding Converter="{StaticResource ConstantLinesConverter}">
        <Binding RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType={x:Type dxc:ChartControl}}" Path="DataContext.DashboardItemName"/>
        <Binding RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType={x:Type dxc:ChartControl}}" Path="DataContext.DashboardControlProvider"/>
    </MultiBinding>
//...
</dxc:ChartControl>
//...
<dxdash:DashboardControl x:Name="dashboardControl1">
  <dxdash:DashboardControl.ChartItemStyle>
    <Style TargetType="dxdash:ChartDashboardLayoutItem">
        <Setter Property="ContentTemplate" Value="{StaticResource chartTemplate}" />
    </Style>
  </dxdash:DashboardControl.ChartItemStyle>
</dxdash:DashboardControl>