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Thread: Drag and Drop in JTrees

  1. #1
    Super Moderator helloworld922's Avatar
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    Default Drag and Drop in JTrees

    Is there a good way to track drags with a mouse listener? Or does anyone here understand how dnd (drag-and-drop) works with JTree? I'm stuck on converting a DefaultMutableTreeNode into a MIME string that I can use with DataFlavor. Ideally, I'd like to be able to have the dnd be done in my application rather than using JTree's (for undo/redo implemented by my application), but I've read from quite a few sources that doing so now is impractical, and it's best to implement a TransferHandler.

    I'm using a basic JTree object with:

    this.tree.getSelectionModel().setSelectionMode(TreeSelectionModel.DISCONTIGUOUS_TREE_SELECTION);
    this.tree.setAutoscrolls(true);
    this.tree.setDragEnabled(true);
    this.tree.setDropMode(DropMode.ON_OR_INSERT);
    this.setTransferHandler(new TestTransferHandler());

    It also has a bunch of nodes that all extend from DefaultMutableTreeNode. It is possible to select multiple nodes that are not next to each other. The TestTransferHandler class is really nothing more than a class that extends TransferHandler (I haven't figured out which methods I need to override, and with what). Also, do I need to have my custom node objects implement Transferable? If so, how would/should I go about this?


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    Administrator copeg's Avatar
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    Default Re: Drag and Drop in JTrees

    Drag and Drop is always a pain in the you know what. Its been a while since I last played with dnd in a JTree, but its similar to dnd in other Components. One needs to implement and set the TransferHandler (createTranferable is one method that should be overridden) and implement/register a DropTargetListener. In the drop method of DropTargetListener, you can use the mouse location from the event to see where the drop needs to go, then deal with the tree rearrangement (and on success you can deal with the undo/redo). In your case transferring multiple nodes that are not consecutive may be a bit complex depending upon your tree structure, so you may need to create a custom Transferable and DataFlavor

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    Super Moderator helloworld922's Avatar
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    Default Re: Drag and Drop in JTrees

    I think I found the answer to my question... It's much more concise than the example given at Sun's website
    Java Tip 97: Add drag and drop to your JTrees. So much work, though. Oh well, I hope it's worth the trouble.

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