UILongPressGestureRecognizer在tableview中被拖动到视图顶部时崩溃 - SWIFT

我使用UILongPressGestureRecognizer为表格视图中的每个单元具有两个节/节标题。当我在第一部分中对单元格进行长按并拖动到表格视图顶部时，我的应用程序崩溃。（我为第二部分禁用了longPressGestureRecognizer）。我在下面一行得到一个异常点，UILongPressGestureRecognizer在tableview中被拖动到视图顶部时崩溃 - SWIFT

var indexPath：NSIndexPath？ = self.routeTableView.indexPathForRowAtPoint（位置）！

我收到此错误调试器，

致命错误：意外发现零而展开的可选值

我的代码如下，

FUNC longPressGestureRecognized（手势：UILongPressGestureRecognizer）{

var state: UIGestureRecognizerState = gesture.state 

    var location:CGPoint = gesture.locationInView(self.routeTableView) 
    var indexPath: NSIndexPath? = self.routeTableView.indexPathForRowAtPoint(location)! 

    if indexPath == nil { 
     return 
    } 

    if indexPath?.section != 1 { 

      switch(state){ 
      case UIGestureRecognizerState.Began: 
       sourceIndexPath = indexPath 

       var cell: UITableViewCell = self.routeTableView .cellForRowAtIndexPath(indexPath!)! as! RouteSelectionCell 

       //take a snapshot of the selected row using helper method 
       snapshot = customSnapshotFromView(cell) 

       //add snapshot as subview, centered at cell's center 
       var center: CGPoint = cell.center 
       snapshot?.center = center 
       snapshot?.alpha = 0.0 
       self.routeTableView.addSubview(snapshot!) 
       UIView.animateWithDuration(0.25, animations: {() -> Void in 
        center.y = location.y 
        self.snapshot?.center = center 
        self.snapshot?.transform = CGAffineTransformMakeScale(1.05, 1.05) 
        self.snapshot?.alpha = 0.98 
        cell.alpha = 0.0 
        }, completion: { (finished) in 
         cell.hidden = true 
       }) 

      case UIGestureRecognizerState.Changed: 
       var center: CGPoint = snapshot!.center 
       center.y = location.y 
       snapshot?.center = center 


       //is destination valid and is it different form source? 
       if indexPath != sourceIndexPath{ 
        //update data source 
        self.messageOptions.exchangeObjectAtIndex(indexPath!.row, withObjectAtIndex: sourceIndexPath!.row) 
        //move the row 
        self.routeTableView.moveRowAtIndexPath(sourceIndexPath!, toIndexPath: indexPath!) 
        //and update source so it is in sync with UI changes 
        sourceIndexPath = indexPath 
       } 

      default: 
       //clean up 
       let cell: UITableViewCell = routeTableView.cellForRowAtIndexPath(sourceIndexPath!)! 
       cell.alpha = 0.0 
       cell.hidden = false 

       UIView.animateWithDuration(0.25, animations: {() -> Void in 

        self.snapshot?.center = cell.center 
        self.snapshot?.transform = CGAffineTransformIdentity 
        self.snapshot?.alpha = 0.0 
        //undo fade out 
        cell.alpha = 1.0 

        }, completion: { (finished) in 
         self.sourceIndexPath = nil 
         self.snapshot?.removeFromSuperview() 
         self.snapshot = nil 
       }) 
       break 
      } 
     } 
    }

任何人都有如何避免这个问题的建议？

来源

2015-07-21 booklynios

当您致电self.routeTableView.indexPathForRowAtPoint(location)!时，您会强制解开返回的值，在这种情况下，它将为零。这是你崩溃的地方。

您的代码应该做这样的事情：

if let indexPath = self.routeTableView.indexPathForRowAtPoint(location) { 
    //do normal code 
} else { 
    //the point didn't map back to a cell! Maybe it was on the header or footer? 
    //Handle this case differently. 
}

另外，我发现这个答案可能会有所帮助：

indexPathForRowAtPoint returns nil only for first cell in a uitableview

来源

2015-07-21 19:46:56 72A12F4E

唉唉。所以我删除了“！”我不再崩溃。但是，当我拖动到视图的顶部时，我的单元格/快照被禁用。它似乎在其他单元格上盘旋。 – booklynios

在else语句中，您将不得不管理如何处理这些特定边界情况。例如，如果它结束在屏幕的顶部，可以将它插入索引0处。如果它位于底部，则将其插入到表格的末尾。 – 72A12F4E

你在说什么snapshot.layer.edgeAntialiasingMask？抱歉。我只有一年多的时间开发。 – booklynios

UILongPressGestureRecognizer在tableview中被拖动到视图顶部时崩溃 - SWIFT

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