Question

我似乎无法让这个工作，我试图在uicollectionview上植入长按手势在SO中发现此代码，现在我只需将其转换为swift，所以我可以使用它探测

obj-c

-(void)handleLongPress:(UILongPressGestureRecognizer *)gestureRecognizer
{
    if (gestureRecognizer.state != UIGestureRecognizerStateEnded) {
        return;
    }

    CGPoint p = [gestureRecognizer locationInView:self.collectionView];

    NSIndexPath *indexPath = [self.collectionView indexPathForItemAtPoint:p];
    if (indexPath == nil){
        NSLog(@"couldn't find index path");
    } else {
        // get the cell at indexPath (the one you long pressed)
        UICollectionViewCell* cell =
            [self.collectionView cellForItemAtIndexPath:indexPath];
        // do stuff with the cell
    }
}

我的快速方法

func handleLongPress(gestureRecognizer: UILongPressGestureRecognizer){
    if (gestureRecognizer.state != UIGestureRecognizerState.Ended){
        return
    }

    let p: CGPoint = gestureRecognizer.locationInView(self.collectionView)
    let indexPath: NSIndexPath = self.collectionView.indexPathForItemAtPoint(p)!
    if (indexPath == nil) {      // Error here 'NSIndexPath' is not convertible to 'UIGestureRecognizerState'
        println("couldn't find index path")

    } else {
        let cell: UICollectionViewCell = self.collectionView.cellForItemAtIndexPath(indexPath)
    }
}

感谢任何帮助，它失败了if（indexPath == nil）错误＆＃39; NSIndexPath＆＃39;不能转换为＆＃39; UIGestureRecognizerState＆＃39;

Answer 1

尝试使用可选绑定来确定optional是否包含值。 indexPathForItemAtPoint返回一个可选值。

if let indexPath = self.collectionView.indexPathForItemAtPoint(p)
{
    let cell: UICollectionViewCell = self.collectionView.cellForItemAtIndexPath(indexPath)
}
else
{
     println("couldn't find index path")
}

阅读Apple快速书中的选项。 https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/TheBasics.html#//apple_ref/doc/uid/TP40014097-CH5-ID309

Answer 2

您还可以使用可选链接并映射可选的索引路径。

let cell = collectionView.indexPathForItemAtPoint(p).map {
  self.collectionView.cellForItemAtIndexPath($0)
}

if let cell = cell {
  // Do something with non-optional cell
} else {
  println("No cell for point")
}

单元格变量是UICollectionViewCell吗？（可选）但这仍然是cellForItemAtIndexPath调用的返回类型。

如果您可以继续或返回可选单元格，则可以跳过整个if let部分，尤其是在您不需要打印错误时（或if cell == nil { println("No cell for point") }

有关处理选项的更多方法，请参阅此博文：How I Handle Optionals In Swift

将Obj-c转换为快速，长按手势

2 个答案: