Entity Relationship Example

GoXam
1

Hi,

Could you provide a code snippet of changing the color of a link in the “Button_Click” event. When I see how you do this I should be able to change the other link properties.

Thanks
Rich

2

Throughout XAML-oriented programming there is always this tension between making programmatic changes “directly” and making changes indirectly and depending on data-binding.

Choice #1:

[code] private void Button_Click(object sender, System.Windows.RoutedEventArgs e) {
// find the Node that contains the Button
Node node = Part.FindAncestor(e.OriginalSource as UIElement);
if (node == null) return;

  // Programmatically toggling the colors of links connected to this node
  Brush brush = new SolidColorBrush(Colors.Orange);
  Brush black = new SolidColorBrush(Colors.Black);
  foreach (Link link in node.LinksConnected) {
    Shape linkshape = link.FindNamedDescendant("Shape") as Shape;
    if (linkshape != null) {
      SolidColorBrush br = linkshape.Stroke as SolidColorBrush;
      if (br != null && br.Color == Colors.Black)
        linkshape.Stroke = brush;
      else
        linkshape.Stroke = black;
    }
  }
}[/code]

Choice #2:

[code] private void Button_Click(object sender, System.Windows.RoutedEventArgs e) {
// find the Node that contains the Button
Node node = Part.FindAncestor(e.OriginalSource as UIElement);
if (node == null) return;

  // Toggling connected link colors via data-binding
  foreach (Link link in node.LinksConnected) {
    Relationship rel = link.Data as Relationship;
    if (rel != null) rel.Color = (rel.Color == "Black" ? "Orange" : "Black");
  }
}[/code]

Choice #2 also requires adding a Color property to the Relationship data class, which I did by just copy-and-paste from the Entity example class and also setting the initial value to “Black”.

And choice #2 requires changing the DataTemplate for links. Instead of setting Stroke=“Black” for the link shape path:

<Path go:LinkPanel.IsLinkShape="True" x:Name="Shape" Stroke="Black" StrokeThickness="1.5" />
Bind it to the Relationship.Color property:

<Path go:LinkPanel.IsLinkShape="True" x:Name="Shape" Stroke="{Binding Path=Data.Color, Converter={StaticResource theStringBrushConverter}}" StrokeThickness="1.5" />
Which choice is best for you depends on the nature of the operation.

Direct changes are sometimes easier to understand and implement.

Changes via data-binding are more tolerant of change, for example when there is a change to the template, or when there are multiple elements that want to use the same color.

Actually, there’s a better choice #2A – declaring the new Relationship.Color property to be a boolean, and defining the two colors in a BooleanBrushConverter in the XAML rather than in the C# code.