好的
我的拖放功能几乎可以完美运行。我长按一个单元格，它可以顺利地将按下的单元格移动到其他两个单元格之间的新位置。表格会调整，更改会保存到核心数据。伟大的！
坏的
我的问题是，如果我将单元格拖到表格底部单元格下方，即使我不放开（取消按下）单元格……应用程序也会崩溃。如果我慢慢拖动，当单元格穿过最后一个单元格的 y 中心时，它真的会崩溃……所以我认为这是与快照获取位置有关的问题。不太重要但可能相关的是，如果我在最后一个带有值的单元格下方长按，它也会崩溃。
拖放运行一个 switch 语句，该语句根据状态运行三组代码之一：
- 新闻开始时的一种情况
- 拖动单元格的一种情况
- 当用户放开单元格时的一种情况
我的代码改编自本教程：
我的代码：
func longPressGestureRecognized(gestureRecognizer: UIGestureRecognizer) {
let longPress = gestureRecognizer as! UILongPressGestureRecognizer
let state = longPress.state
var locationInView = longPress.locationInView(tableView)
var indexPath = tableView.indexPathForRowAtPoint(locationInView)
struct My {
static var cellSnapshot : UIView? = nil
}
struct Path {
static var initialIndexPath : NSIndexPath? = nil
}
let currentCell = tableView.cellForRowAtIndexPath(indexPath!) as! CustomTableViewCell;
var dragCellName = currentCell.nameLabel!.text
var dragCellDesc = currentCell.descLabel.text
//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 && 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
var appDel: AppDelegate = (UIApplication.sharedApplication().delegate as! AppDelegate)
var context: NSManagedObjectContext = appDel.managedObjectContext!
var fetchRequest = NSFetchRequest(entityName: currentListEntity)
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)) {
swap(&taskList_Cntxt[indexPath!.row], &taskList_Cntxt[Path.initialIndexPath!.row])
tableView.moveRowAtIndexPath(Path.initialIndexPath!, toIndexPath: indexPath!)
toolBox.updateDisplayOrder()
context.save(nil)
Path.initialIndexPath = indexPath
}
}
default:
if My.cellSnapshot != nil && indexPath != nil {
//Runs continuously while a long press is recognized (I think)
//Animates cell movement
//Completion block:
//Removes snapshot of cell, cleans everything up
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 {
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 longPressGestureRecognized
潜在的罪魁祸首
我的猜测是，这个问题与单元格一旦低于最后一个单元格就无法获取坐标有关。它并不是真正的浮动，它不断地设置它相对于其他单元格的位置。我认为解决方案将是一个 if 语句，当一个位置没有单元格可参考时，它会做一些神奇的事情。但是什么！？！由于某种原因，为每个案例添加 nil 检查不起作用。
明确提出的问题
如何避免崩溃并处理拖动的单元格被拖到最后一个单元格下方的事件？
崩溃截图：
