To exactly specify where the item will be dropped, you will need to introduce a field that sets the item ordering, and set this field in the data item prior to inserting, based on the drop event handler. You would also need to enforce that the dataSource is sorted by that field.
If you do not need the ordering field in your business layer (i.e. ordering the items is only meant to serve as feedback for the user), you may pop a status message that the operation was successful.
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