Linkable

GoXam
1

Hi,

I’ve nearly got to grips with the programming model, but occasionally get stuck and, after spending my day trying to resolve this myself, I have to give up and ask …

Part of the graph tool that I am building requires that, if a node has any connected links, then it cannot be dropped onto a Group node. This only applies to Group nodes that are not linkableTo or LinkableFrom.

I have a number of different templates that I use for the Groups, the one below defines that it is neither linkable to or from.

        <DataTemplate x:Name="PrioritizeTemplate">
            <go:NodePanel Style="{StaticResource SpotPanelStyle}" 
						  go:Node.LinkableFrom="False"
						  go:Node.LinkableTo="False"
						  go:Part.DropOntoBehavior="AddsToGroup"
					>
                    <TextBlock
						HorizontalAlignment="Left"
						VerticalAlignment="Top"
						Style="{StaticResource TextBlockStyle}" 
						Text="{Binding Data.Text, Mode=OneWay}" Foreground="White" />
            </go:NodePanel>
        </DataTemplate>

When I run this code, the diagram edit honours the LinkableFrom and LinkableTo conditions, but what I need to do is, before I allow a node to be dropped onto it (I have a custom DraggingTool) - I want to check that evaluate the LinkableFrom/To properties on the Group node.

I have used the static methods on the Group/Node classes, but they always return null…

            var top = this.Diagram.Panel.FindElementsAt<Group>(pt,
                                                                 Part.FindAncestor<Group>,
                                                                 px => !Diagram.SelectedParts.Contains(px),
                                                                 SearchLayers.Parts).FirstOrDefault();
 
            var linkableFrom = Group.GetLinkableFrom(top);
            var linkableTo = Group.GetLinkableTo(top);

The above code is called during a ConsiderDragOver method. The “top” returns the Group that I am expecting - but the GetLinkableFrom/To always returns a null.

I know that it’s going to something obvious, but can’t get to the bottom of it.

On another note … How do I enable the whole surface area of the Group node to be LinkStart’able and LinkEnd’able ?

2

I have resolved the issue of making the whole Group area to be LinkStartable/Endable …

I had modified the LinkingTool so that it only starts when the Ctrl key is pressed - but this also has the effect of altering the logic that enables the link to be dropped anywhere on the Group’s surface.

3

Which override method is your code in?
It’s normal to override DraggingTool.IsValidMember in order to decide whether add a particular Node is acceptable to a Group.
Using that method would mean you don’t have to search for the Group that it’s over.
I’m wondering if maybe you’re getting a different Group.

BTW, it’s a bit odd to be adding nodes to groups that don’t use a GroupPanel or at least some good sized Panels. It means that the added nodes won’t be visually “within” the group.

EDIT: oops – crossing messages…

4

Thanks for the speed response.

Thanks, I willl use the IsValidMember method override. Your program model is so extensible, it’s sometimes difficult to identify the correct override!

I have implemented a new Layout and DragDrop scheme, which allows a node to be reordered within a Group box. The layout scheme is basically an implementation of the GridLayout - but has extensions to enable the contained children to be reorganised by dragging the contained node to the new location within the Group.

I’m not entirely sure if I am re-inventing the wheel - but it works - that is - only if I use a NodePanel. If I use a GroupPanel, there are side effects (related to child positioning) - that I could not code around.

I’m quite happy with what I’ve developed - but am now stuck on the part where I need to progmattically identify if a node/group can accept links to/from. I’m sure that I’m doing it correctly, but I’m obviously missing something!

5

Sorted it ...

Confusion over FrameworkElements …

To access the DependencyProperties I should have been using the VisualElement - not the Node/Group object.