How to prevent connections manipulation.

[Maxim]

How to prevent attach connection to shape, detach connection from shape and delete connection from diagram? I want to make decision on ObservableGraphSourceBase level.

[Petar Mladenov]

Hi Maxim,

To be honest the connection manipulation is not well suited for MVVM. The best way to handle it is via ConnectionManiopulation events.

For GraphSource handling of connection creating, removing and inserting in graphsource you can override the following methods of GraphSoureBase:

public override void AddLink(Link link)
       {
           base.AddLink(link);
       }

       public override ILink CreateLink(object source, object target)
       {
           return base.CreateLink(source, target);
       }

       public override bool RemoveLink(Link link)
       {
           return base.RemoveLink(link);
       }

When you set Source or Target (which can also be set internally, in Diagram's core code), the OnPropertyChanged of the LinkViewModelBase will be fired, so you can try some code like:

public class Link : LinkViewModelBase<NodeViewModelBase>
    {
        protected override void OnPropertyChanged(string propertyName)
        {
            if (propertyName == "Target" && this.Target != null)
            {
                // your custom logic here
                this.Target = null;
            }
            base.OnPropertyChanged(propertyName);
        }

I hope this will help you move forward.

Regards,
Petar Mladenov
Progress Telerik