iOS：如何在长按时启用 UIScrollView 平移

Question

我可以使用scrollView.scrollEnabled 属性有效地启用/禁用滚动。

目前我在longPressRecognizer 的状态为UIGestureStateBegan 时启用滚动，并在UIGestureStateEnded 时禁用滚动。

当我长按然后拖动手指时，scrollView 不会滚动。

我认为 scrollView 的 panGestureRecognizer 不知何故没有收到触摸事件，这很奇怪，因为 scrollView 是 （我使用 touchesBegan、touchesMoved 等方法进行了检查）。

Answer 1

UIScrollView 没有被触摸，因为触摸是在您启用 UIScrollView 上的滚动之前开始的。此示例代码使用 UILongPressGestureRecognizer 为您管理滚动，滚动一个大 UIImageView：

@IBOutlet weak var scrollView: UIScrollView!
@IBOutlet var gr: UILongPressGestureRecognizer!
var initialPos = CGPointZero
var dragPos = CGPointZero

// This action is bound to long press gesture recognizer within Interface Builder
@IBAction func longpressHandler(sender: UILongPressGestureRecognizer) {
    if sender.state == .Began {
        // Save initial position for moving
        initialPos = sender.locationInView(scrollView)
    }
    else if sender.state == .Changed {
        // Get new drag location
        let loc = sender.locationInView(scrollView)
        let newPos = CGPoint(x: initialPos.x - loc.x + dragPos.x, y: initialPos.y - loc.y + dragPos.y)
        dragPos = newPos
        scrollView.contentOffset = newPos
    }
    else if sender.state == .Ended {
        // Check for end position of the content, snap it back to the edge of the screen if moved too far
        var newOffset = scrollView.contentOffset
        var move = false
        if scrollView.contentOffset.x < 0 {
            newOffset.x = 0
            move = true
        }
        if scrollView.contentOffset.y < 0 {
            newOffset.y = 0
            move = true
        }
        if scrollView.contentOffset.x > photo.frame.size.width - scrollView.frame.size.width {
            newOffset.x = max(self.photo.frame.size.width - self.scrollView.frame.size.width, 0)
            move = true
        }
        if scrollView.contentOffset.y > photo.frame.size.height - scrollView.frame.size.height {
            newOffset.y = max(self.photo.frame.size.height - self.scrollView.frame.size.height, 0)
            move = true
        }
        if move {
            UIView.animateWithDuration(0.25, animations: {
                self.scrollView.contentOffset = newOffset
            })
        }
    }
}

var photo = UIImageView(image: UIImage(named: "photo"))

override func viewDidLoad() {
    super.viewDidLoad()

    // Set up your scrollview
    scrollView.addSubview(photo)
    scrollView.contentSize = photo.frame.size

    // add the long press gesture recognizer to the scrollview
    scrollView.addGestureRecognizer(gr)
}