Hello there,

You cannot select nodes when they are locked, you will have to set Locked to false first. If you need selection to work while preventing end-users from modifying a node, set node.EnabledHandles to None. If you need a kind of read-only mode for whole diagram, set the Behavior property to either DoNothing or SelectOnly.

You can select nodes from code-behind by setting their Selected property, or by calling diagram.Selection methods like Add, Toggle, Change.

Regards,
Slavcho
Mindfusion