swift - 跟踪 NSCell 的位置变化

Question

我有一个 NSTableView，当用户滚动 tableView 时，我想跟踪包含它的 NSCell 的位置。

我找不到任何有用的东西。如果有人能引导我走向正确的方向，那就太好了!

编辑:

感谢 @Ken Thomases 和 @Code Different，我刚刚意识到我正在使用基于 View 的 tableView，使用 tableView(_ tableView:viewFor tableColumn:row:)，它返回一个 NSView。

但是，NSView 本质上是一个 NSCell。

let cell = myTableView.make(withIdentifier: "customCell", owner: self) as! MyCustomTableCellView // NSTableCellView

所以我真的希望我最初的问题没有误导。我仍在寻找一种方法如何跟踪单个单元格/ View 的位置。

我在 IB 中将 NSScrollView(包含 tableView)的行为设置为 Copy on Scroll。

但是当我检查 View /单元格 frame 的 x 和 y(在我的 MyCustomTableCellView 子类的 viewWillDraw 中)时，它仍然是 0, 0.

Answer 1

NSScrollView 不使用委托(delegate)。它使用通知中心通知观察者发生了变化。下面的解决方案假设垂直滚动。

override func viewDidLoad() {
    super.viewDidLoad()

    // Observe the notification that the scroll view sends out whenever it finishes a scroll
    let notificationName = NSNotification.Name.NSScrollViewDidLiveScroll
    NotificationCenter.default.addObserver(self, selector: #selector(scrollViewDidScroll(_:)), name: notificationName, object: scrollView)

    // Post an intial notification to so the user doesn't have to start scrolling to see the effect
    scrollViewDidScroll(Notification(name: notificationName, object: scrollView, userInfo: nil))
}

// Whenever the scroll view finished scrolling, we will start coloring the rows
// based on how much they are visible in the scroll view. The idea is we will
// perform hit testing every n-pixel in the scroll view to see what table row
// lies there and change its color accordingly
func scrollViewDidScroll(_ notification: Notification) {
    // The data's part of a table view begins with at the bottom of the table's header
    let topEdge = tableView.headerView!.frame.height
    let bottomEdge = scrollView.bounds.height

    // We are going to do hit-testing every 10 pixel. For best efficiency, set
    // the value to your typical row's height
    let step = CGFloat(10.0)

    for y in stride(from: topEdge, to: bottomEdge, by: step) { 
        let point = NSPoint(x: 10, y: y)                        // the point, in the coordinates of the scrollView
        let hitPoint = scrollView.convert(point, to: tableView) // the same point, in the coordinates of the tableView

        // The row that lies that the hitPoint
        let row = tableView.row(at: hitPoint)

        // If there is a row there
        if row > -1 {
            let rect = tableView.rect(ofRow: row)                     // the rect that contains row's view
            let rowRect = tableView.convert(rect, to: scrollView)     // the same rect, in the scrollView's coordinates system
            let visibleRect = rowRect.intersection(scrollView.bounds) // the part of the row that visible from the scrollView
            let visibility = visibleRect.height / rowRect.height      // the percentage of the row that is visible

            for column in 0..<tableView.numberOfColumns {
                // Now iterate through every column in the row to change their color
                if let cellView = tableView.view(atColumn: column, row: row, makeIfNecessary: true) as? NSTableCellView {
                    let color = cellView.textField?.textColor

                    // The rows in a typical text-only tableView is 17px tall
                    // It's hard to spot their grayness so we exaggerate the
                    // alpha component a bit here:
                    let alpha = visibility == 1 ? 1 : visibility / 3

                    cellView.textField?.textColor = color?.withAlphaComponent(alpha)
                }
            }
        }
    }
}

结果: