用户完成拖放操作后重新排列多个选定的列表视图项

Question

INTRODUCTON:

I am working on a drag and drop feature of the listview. I am stuck at the last step -> rearranging multiple selected items after user finishes drag and drop.

QUESTION:

Can you explain me the algorithm that implements item rearrangment?

I have the index of the clicked item after user releases the mouse. I have indexes of dragged items and their count. Pseudo code is acceptable as well, but be warned that I might have follow up questions.

NOTE:

This post has been edited in response to the comments that claimed my original question did not seek user friendly implementation.

The point is to implement standard drag & drop behavior, and the reason I phrased my question poorly at the first place was my lack of experience with this topic.

If further clarifications are required I will update my post.

Regards.

Answer 1

Normal drag & drop reordering removes the selected items and reinserts them in the new spot. It would be pretty unintuitive for the existing items in the new spot to jump to where the old ones came from.

To implement "standard" reordering, basically you:

• Remember the index of the item below where the user drags your items to. In your example above, this would be 5 (assuming the new items are to be inserted above Item 6)
• Remove the dragged items from the list one at a time using LVM_DELETEITEM
• If the dragged items were originally above the new position, subtract the total number of dragged items from the index you remembered in step 1. This would give us 2 using the examples above.
• Finally, reinsert the dragged items at the remembered index (remembering to increment the new index for each additional item). For example, the first dragged item would be inserted at position 2 , then the next at 3 and so on.

Also note you need special handling for the case where the items are dragged to the top of the list. In that case, you would start the insertion at 0 , then 1 and so on.