java - Drag and Drop in JTree - can importData modify the tree? -


i experiencing difficulty drag , drop in jtree component. drag , drop allow user rearrange nodes in tree. implementation works fine, in situations there null pointer exception when moving node in between of children, on picture below dragging c under b (between b , a):

drag between children

the direct cause of exception seems while performing cleanup of dnd framework, path item being dragged invalidated changes have performed on tree implement required move.

more specifically, callstack this:

javax.swing.plaf.basic.basictreeui#getdroplinerect java.beans.propertychangesupport#firepropertychange ... javax.swing.transferhandler.drophandler#cleanup ... javax.swing.transferhandler.swingdroptarget#drop

the getdroplinerect attempting evaluate rectangle path in tree no longer exists, node deleted when move performed in importdata function.

my question is: expected? considered unsafe perform data changes while dnd has not completed yet, , should queued , performed later? did not see such requirement in documentation, , did not see such async implementation in of examples or tutorials.

imho not saver - stated - data modifications after drop occured, easier implement. if remove node on drag event, need have rollback @ hand handle situation of removing node window or making illegal drop. on other hand, if use drag event gain needed information successful drop , don't change in data yet, stated problems dissapear. on drop, use remembered information drag , complete whole operation, or discard drop, in return rollbacks visual actions (though i'm not 100% sure here), remaining consistent state time.

edit: "my question is: expected?": think exception occurs logic of changing tree model in between drag , drop, making inconsitent @ time event dispatching thread trying redraw model. apologies not being able state "this how it's done", maybe else finds quote swing tree dnd doc.


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