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POWanted : Theory for Copy, Move in Nodes in Trees (such as Drag and Drop)
 

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  1. POWanted : Theory for Copy, Move in Nodes in Trees (such as Drag and Drop)
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    <p>One of my apps maintains a tree of objects, displayed in an outline view. I've implemented a long routine for moving or copying object(s) from one node to another. This routine is invoked, for example, when the user executes a drag and drop in the outline view.</p> <p>It gets to be fun when objects are moved within the same parent. Or when objects are not allowed at certain nodes, although I do allow the user to drop them there, I helpfully adjust their final location. After several weeks, and a few bug fixes during the first few releases, I got this routine to always behave as expected. I think. But I'm not sure, because this method was developed <em>ad hoc</em>. That means: When I found something that didn't work, I fixed it.</p> <p>Currently I'm working on improving its performance in a few corner cases. For example, code which re-indexes all affected nodes immediately after each any object is moved is logically bullet-proof, but costly when the user moves 1000 items in at the head of a node already containing 1000 items.</p> <p>As I look at this code, it seems to me that some computer scientist might at some point have written a textbook chapter or something on this topic, and I should buy that book, read it, rip out my <em>ad hoc</em> code and do it the <em>right</em> way. But I can't find any in a web search. Does anyone know of any such book?</p> <p>Or maybe not. Maybe this is one of those cases where, after all is said and done, each application too different to propose a general solution?</p> <p>Thanks,</p> <p>Jerry Krinock</p>
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