Drag to empty section

[jhollez]

Everything works fine as long as there are other cells in a section, but when you drag all cells away, there is no way to drag them back to the now empty section. Also sections that are empty from the start can't receive dragged cells. Is there a way to make this work?

[shusta]

Hmm, I didn’t check for this scenario at all. You’re right, though. And UITableView’s built-in editing mode properly handles empty sections so I should match it.

I’m a little pressed for time this week but I think I could find some free time later this month to look at this. If you want to take a crack at it, be my guest. You’ll want to look in the -shuffleCellsOutOfWayOfDraggedCellIfNeeded method. It looks like it just needs to check the dragged cell’s frame against the tableview’s -rectForSection: and similar methods.

[jhollez]

It would be great if you could have a look. I will also try this weekend to see if I can help resolve this issue.
In any case, thanks for your component, it's much more usable then the default one.
There's one other issue I noticed that the original apple component has. When there's no header or footer and no cells in the first section or the last section, it's impossible to drag cells there, since they can't be dragged far enough. Would be great if the solution for draging to emty sections could include these borderline cases.

[timothyarmes]

I've hit this too - no solution forthcoming ? :(

[shusta]

Not immediately forthcoming, no. I'm really sorry about that, lost track that I was going to do this. And now things are kinda frantic since I'm 2 feet from graduating college.

[timothyarmes]

That's OK, I've got this working in my version. However there's a big in UITableView that causes a strange cell reloading animation on a row that has a blank section above it. To get around this I've had to avoid reloading the cell in your code, which is fine in my specific case, but not great in general.

For that reason I won't be posting a pull request on this mod.

Tim

[joslinm]

Anytime for this @shusta ? Or @timothyarmes , might you share with me how you fixed it? I really like this but without being able to drag into an empty section, I can't incorporate it into my project.

[davehakim]

No idea how well (or otherwise) this mod would work with tableviews with cells of different heights but in my case it appears to solve the empty section problem. It could definitely be improved. I'm replacing top half of shuffleCellsOutOfWayOfDraggedCellIfNeeded with code that moves the blank cell up or down by a single row depending on where the dragitem is relative to it. It would likely be better to look at exactly what table view rows and sections are being overlapped by the dragitem in the way the current code does for rows (as @shusta suggested) but this appears to work for me for the moment. Also, I'm only considering tables with section headers. No accounting is made for section footers.

- (NSIndexPath*) indexPathBeforeBlankCellIndex : (NSIndexPath*)blankCellIndex {

    if(blankCellIndex.row > 0 ) {
        return [NSIndexPath indexPathForRow:blankCellIndex.row - 1 inSection:blankCellIndex.section];
    } else if (blankCellIndex.section > 0) {
        return [NSIndexPath indexPathForRow:[self.tableView numberOfRowsInSection:blankCellIndex.section-1] inSection:blankCellIndex.section-1];
    }

    return blankCellIndex; // can't go up
}

- (NSIndexPath*) indexPathAfterBlankCellIndex : (NSIndexPath*)blankCellIndex {

    // Subtract 1 from the row count before moving forward because this section contains the blank cell
    if(blankCellIndex.row < [self.tableView numberOfRowsInSection:blankCellIndex.section] - 1) {
        return [NSIndexPath indexPathForRow:blankCellIndex.row + 1 inSection:blankCellIndex.section];
    } else if (blankCellIndex.section < self.tableView.numberOfSections) {
        return [NSIndexPath indexPathForRow:0 inSection:blankCellIndex.section+1];
    }

    return blankCellIndex; // can't go down
}

/*
 Description:
 If necessary, move blank cell so that it appears that the tableview's cells are shuffling out of the way of the draggedCell
 */

- (void)shuffleCellsOutOfWayOfDraggedCellIfNeeded {

    /*
        Use blank rect instead of the cell itself. The cell might be offscreen and thus nil.
        Blank cell might not be covered either, if the dragged cell is smaller than the nearby cell.
     */
    CGRect blankCellFrame = [self.tableView rectForRowAtIndexPath:self.indexPathBelowDraggedCell];

    /*
        nil unless we actually are going to move cells.
     */
    NSIndexPath *rowToMoveTo = nil;


    /*
     We may want to move if the center point of the dragged cell is above the blank cell ...
     */
    if (draggedCell.center.y < blankCellFrame.origin.y) {

        CGRect sectionHeaderRect = [self.tableView rectForHeaderInSection:self.indexPathBelowDraggedCell.section];
        float sectionMidpointY = sectionHeaderRect.origin.y + sectionHeaderRect.size.height / 2;

        if (!self.indexPathBelowDraggedCell.row == 0 || draggedCell.center.y < sectionMidpointY)
            rowToMoveTo = [self indexPathBeforeBlankCellIndex:self.indexPathBelowDraggedCell];

    /*
     Or below it
     */
    } else if (draggedCell.center.y > blankCellFrame.origin.y + blankCellFrame.size.height) {


        if(self.indexPathBelowDraggedCell.row < [self.tableView numberOfRowsInSection:self.indexPathBelowDraggedCell.section] - 1
             || self.indexPathBelowDraggedCell.section + 1 < self.tableView.numberOfSections){

            rowToMoveTo = [self indexPathAfterBlankCellIndex:self.indexPathBelowDraggedCell];
        }
    /*
     Or one very special case if we're potentially dealing with what was the very last row in a section all by itself
     */
    } else if (self.indexPathBelowDraggedCell.row == [self.tableView numberOfRowsInSection:self.indexPathBelowDraggedCell.section] - 1 && self.indexPathBelowDraggedCell.section < self.tableView.numberOfSections - 1 && [self.tableView numberOfRowsInSection:self.indexPathBelowDraggedCell.section+1] == 0) {

        /* 
         In this case if we hit bottom we want to move back to the last section ... Apple must be doing something private to give
         its drag items more space to move below the current bounds of the table view
         */
        CGRect sectionHeaderRect = [self.tableView rectForHeaderInSection:self.indexPathBelowDraggedCell.section+1];
        if (draggedCell.frame.origin.y + draggedCell.frame.size.height == sectionHeaderRect.origin.y + sectionHeaderRect.size.height) {
            rowToMoveTo = [self indexPathAfterBlankCellIndex:self.indexPathBelowDraggedCell];
        }
    }


    /*
        If the dragged cell is covering a new row that isn't the one with the blank item, move the blank item to that new row.
     */
    if (rowToMoveTo != nil && !(rowToMoveTo.section == self.indexPathBelowDraggedCell.section && rowToMoveTo.row == self.indexPathBelowDraggedCell.row)) {
        /*
            Tableview's dataSource must update before we ask the tableview to update rows.
         */
        [self.tableView.dataSource tableView:self.tableView moveRowAtIndexPath:self.indexPathBelowDraggedCell toIndexPath:rowToMoveTo];

        /*
            Update the blank index path
         */
        NSIndexPath *formerBlankIndexPath = self.indexPathBelowDraggedCell;
        self.indexPathBelowDraggedCell = rowToMoveTo;

        /*
            Then animate the row updates.
         */
        if ( [self.tableView respondsToSelector:@selector(moveRowAtIndexPath:toIndexPath:)] )
            [self.tableView moveRowAtIndexPath:formerBlankIndexPath toIndexPath:rowToMoveTo];
        else {
            [self.tableView beginUpdates];
            [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:formerBlankIndexPath] withRowAnimation:UITableViewRowAnimationNone];
            [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:self.indexPathBelowDraggedCell] withRowAnimation:UITableViewRowAnimationNone];
            [self.tableView endUpdates];
        }


        /*
            Keep the cell under the dragged cell hidden.
            This is a crucial line of code. Otherwise we get all kinds of graphical weirdness
         */
        UITableViewCell *cellToHide = [self.tableView cellForRowAtIndexPath:self.indexPathBelowDraggedCell];
        cellToHide.hidden = YES;

    }
}