Question

I’ve been trying to rack my head over this but it’s just not working.

I’m using some proprietary technology that only allows the move of a single element at a time. Super annoying. Think of it as list.moveRow(before, after).

So imagine a todo list with 10 items in it: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

What I want to do is reorder multiple items in there,
so say I select items 2, 6, 7, and 8.

Then I drag and drop to position 4.

The idea is that the elements would now be in order: 1, 3, 2, 6, 7, 8, 4, 5, 9, 10.

Is there a simple way to do this? I tried using extra variables to keep track of offsets due to an element moved that throws off the index, but it’s super messy. 🙁

Answer 1

Sat down and wrote it out, and came up with a reasonable solution. This seems to work fine:

// Reorder list
function reorder(items, index)
{        
    // When we move, we have to account for previously moved rows too
    //  Go from bottom-most selected row first to preserve order
    for (var i = items.length - 1, itemOffset = 0, indexOffset = 0; i >= 0; --i) 
    {
        // Move
        list.moveRow(items[i] + itemOffset, index + indexOffset);

        // Change offsets based on location
        //  If next row index is after target index, add to row offset
        if (i-1 >= 0 && items[i-1] >= index) {
            itemOffset++;
        } else {    // If next index is before target, subtract from target
            itemOffset= 0;
            indexOffset--;
        }
    }
}