Drag & Drop Works - Autoscroll Doesn't

Question

I have a drag and drop function (code below) for my table that works great. Except, I can't drag a cell to a location not showing on screen / in view.

In other words, I haven't figured out how to make it autoscroll.

Is anyone able to look at my code and know where to add code that enables autoscrolling when the user drags the cell towards the top or bottom of the view?

func animateCellDrag (gestureRecognizer: UIGestureRecognizer, tableView: UITableView, whichList: String) {

    let longPress = gestureRecognizer as! UILongPressGestureRecognizer
    let state = longPress.state
    var locationInView = longPress.locationInView(tableView)
    var indexPath = tableView.indexPathForRowAtPoint(locationInView)
    var count = 0

    struct My {
        static var cellSnapshot : UIView? = nil
    }
    struct Path {
        static var initialIndexPath : NSIndexPath? = nil
    }

    if indexPath != nil {
        //Steps to take a cell snapshot. Function to be called in switch statement
        func snapshotOfCell(inputView: UIView) -> UIView {
            UIGraphicsBeginImageContextWithOptions(inputView.bounds.size, false, 0.0)
            inputView.layer.renderInContext(UIGraphicsGetCurrentContext()!)
            let image = UIGraphicsGetImageFromCurrentImageContext() as UIImage
            UIGraphicsEndImageContext()
            let cellSnapshot : UIView = UIImageView(image: image)
            cellSnapshot.layer.masksToBounds = false
            cellSnapshot.layer.cornerRadius = 0.0
            cellSnapshot.layer.shadowOffset = CGSizeMake(-5.0, 0.0)
            cellSnapshot.layer.shadowRadius = 5.0
            cellSnapshot.layer.shadowOpacity = 0.4
            return cellSnapshot
        }

        switch state {
        case UIGestureRecognizerState.Began:
            //Calls above function to take snapshot of held cell, animate pop out
            //Run when a long-press gesture begins on a cell
            if indexPath != nil {
                Path.initialIndexPath = indexPath
                let cell = tableView.cellForRowAtIndexPath(indexPath!) as UITableViewCell!
                My.cellSnapshot  = snapshotOfCell(cell)
                var center = cell.center

                My.cellSnapshot!.center = center
                My.cellSnapshot!.alpha = 0.0

                tableView.addSubview(My.cellSnapshot!)

                UIView.animateWithDuration(0.25, animations: { () -> Void in
                    center.y = locationInView.y

                    My.cellSnapshot!.center = center
                    My.cellSnapshot!.transform = CGAffineTransformMakeScale(1.05, 1.05)
                    My.cellSnapshot!.alpha = 0.98

                    cell.alpha = 0.0

                    }, completion: { (finished) -> Void in

                        if finished {
                            cell.hidden = true
                        }
                })
            }
        case UIGestureRecognizerState.Changed:

            if My.cellSnapshot != nil || indexPath != nil {
                //Runs when the user "lets go" of the cell
                //Sets CG Y-Coordinate of snapshot cell to center of current location in table (snaps into place)
                var center = My.cellSnapshot!.center
                center.y = locationInView.y
                My.cellSnapshot!.center = center

                let appDel: AppDelegate = (UIApplication.sharedApplication().delegate as! AppDelegate)
                let context: NSManagedObjectContext = appDel.managedObjectContext!
                let fetchRequest = NSFetchRequest(entityName: whichList)
                let sortDescriptor = NSSortDescriptor(key: "displayOrder", ascending: true )
                fetchRequest.sortDescriptors = [ sortDescriptor ]

                //If the indexPath is not 0 AND is not the same as it began (didn't move): Update array and table row order
                if ((indexPath != nil) && (indexPath != Path.initialIndexPath) && (indexPath?.row < taskList_Cntxt.count)) {

                    switch whichList {
                        case "TodayTask", "TomTask", "TBDTask", "FinTask":
                            swap(&taskList_Cntxt[indexPath!.row], &taskList_Cntxt[Path.initialIndexPath!.row])
                            tableView.moveRowAtIndexPath(Path.initialIndexPath!, toIndexPath: indexPath!)
                            toolBox.updateDisplayOrder()
                        default:
                            swap(&curLifeList_Context[indexPath!.row], &curLifeList_Context[Path.initialIndexPath!.row])
                            tableView.moveRowAtIndexPath(Path.initialIndexPath!, toIndexPath: indexPath!)
                            toolBox.llvc_updateDisplayOrder()
                    }

                    do {
                        try context.save()
                    } catch _ { print("Drag and drop error. State: Changed")}

                    Path.initialIndexPath = indexPath
                }
            }
        default:
            if My.cellSnapshot != nil || indexPath != nil {
                //Runs continuously while a long press is recognized / Animates cell movement
                let cell = tableView.cellForRowAtIndexPath(Path.initialIndexPath!) as UITableViewCell!

                cell.hidden = false
                cell.alpha = 0.0
                UIView.animateWithDuration(0.25, animations: { () -> Void in
                    My.cellSnapshot!.center = cell.center
                    My.cellSnapshot!.transform = CGAffineTransformIdentity
                    My.cellSnapshot!.alpha = 0.0
                    cell.alpha = 1.0
                    }, completion: { (finished) -> Void in
                        if finished {
                            //Completion block removes snapshot of cell, cleans everything up
                            Path.initialIndexPath = nil
                            My.cellSnapshot!.removeFromSuperview()
                            My.cellSnapshot = nil
                        }
                })//End of competion block & end of animation
            }//End of 'if nil'
        }//End of switch
    }//End of longPress if-nil
}//End of longPressGestureRecognized

Answer 1

I was able to resolve it using this code:

if locationOnScreen.y < 200 && indexPath!.row > 1 {
    let indexPath = NSIndexPath(forRow: indexPath!.row-1, inSection: 0)
    tableView.scrollToRowAtIndexPath(indexPath, atScrollPosition: UITableViewScrollPosition.Top, animated: false)
} else if locationOnScreen.y > 550 && indexPath!.row < listCount {
    let indexPath = NSIndexPath(forRow: indexPath!.row+1, inSection: 0)
    tableView.scrollToRowAtIndexPath(indexPath, atScrollPosition: UITableViewScrollPosition.Bottom, animated: false)
}

Where:

var locationOnScreen = longPress.locationInView(tableView.superview)
listCount = listArrayOrContext.count

Inserted in the switch case:

case UIGestureRecognizerState.Changed:

I set animate to false because otherwise I got very jerky, messy scrolling. If anyone figures out how to get a slow, gradual scroll, please post it.