Prevent a Connection creation, by looking its ToConnectionPoint

Hello,

I tried to prevent a Connection creation (I look at my conditions and then I try to remove the Connection) in a ConnectionsCollectionChange event, but it doesn't work. I know it's because I can't edit the Collection when I am in his Change event. It's OK for me.

But can I do this implementation somewhere else? I want to prevent a Connection creation depending on the FromConnectionPoint and the ToConnectionPoint. The final aim is to prevent a 'loop' in the connections, there mustn't be any loop of Nodes/Connections on the Diagram.

Thank you !

Leon

Hello Leon

Yes we provide a convenient place for this logic to be placed. What you'll want to do is create a class that implements the IDiagramConnectionBuilder interface. In the CanCreateConnection method, you get the fromConnectionPoint as a parameter, and dropTarget.ConnectionPoint provides the destination connection point. If the dropTarget or dropTarget.ConnectionPoint is null, just return true. Otherwise, if the two connection points exist on the same node (i.e. they have the same Connectable property value) then return false. In the CreateConnection method, simply create an instance of whatever type of connection you want - using the two given connection points, and then add that connection instance to the diagram.Connections collection.

Let me know if you have any questions about this.

-Jason Fauchelle

Hi Jason,

Thank you for your answer, I understood what you explained to me, but how can I tell to the diagram to use my ConnectionBuilder class instead of the default ConnectionBuilder class?

Thank you.

Hello Leon

Ah yes, I'd forgotten to mention. This can be done by setting the DefaultConnectionBuilder property of the IDiagramModel. (Your diagram model is probably an instance of the Diagram class). Let me know if you have questions about this.

-Jason Fauchelle

Ok nice, thank you Jason.

I wrote this code :

public class my_connectionBuilder : IDiagramConnectionBuilder
{
    bool IDiagramConnectionBuilder.CanCreateConnection(IDiagramModel diagram, IDiagramConnectionPoint fromConnectionPoint, ConnectionDropTarget dropTarget)
    {
        if (fromConnectionPoint.Connectable.GetType().ToString().EndsWith("Node"))
            return true;
        return false;
    }

    void IDiagramConnectionBuilder.CreateConnection(IDiagramModel diagram, IDiagramConnectionPoint fromConnectionPoint, IDiagramConnectionPoint toConnectionPoint)
    {
        if (fromConnectionPoint.Connectable != toConnectionPoint.Connectable)
        {
            var coco = new DiagramConnection((DiagramConnectionPoint)fromConnectionPoint, (DiagramConnectionPoint)toConnectionPoint);
            diagram.Connections.Add(coco);
        }
    }
}

And I had to create a new Diagram instance (I didn't succeed in change DefaultConnectionBuilder of default ds.Diagram (readonly)) :

var coco = new Diagram();
coco.DefaultConnectionBuilder = new my_connectionBuilder();
ds.Diagram = coco;

And now it works.

Hello Leon

Great to hear you've got it all working.

-Jason Fauchelle