Swift - Fading cells in UITableView

问题:

I'm having troubles with my UITableView in swift on Xcode 6 :

I would like my UITableView cells to fade in / out when appearing / disappearing.

I looked a lot on the web for fade animations but I didn't find what I wanted because it's based on duration animations.

I Think what I need is sort of mask based on alpha ? I'm not sur and I don't even know have to create one...

I have a UIViewController containing a tableView and some blank space (for now) upside and downside of the UITableView.

Thank's for your help !!

Best,

Anatole

回答1:

animateWithDuration seems appropriate, since the fade in/out has a duration: the cell gradually becoming visible or invisible over time.

Here is an example of making table cells fade-in:

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

    var cell = self.tableView.dequeueReusableCellWithIdentifier("cell") as UITableViewCell

    cell.textLabel?.text = self.items[indexPath.row]
    cell.backgroundColor = UIColor.grayColor()
    cell.alpha = 0

    UIView.animateWithDuration(2, animations: { cell.alpha = 1 })

    return cell
}

EDIT:

This sets the cell's alpha based on their y position, which is probably closer to what you want:

func scrollViewDidScroll(scrollView: UIScrollView) {

    for cell in tableView.visibleCells() as [UITableViewCell] {

        var point = tableView.convertPoint(cell.center, toView: tableView.superview)
        cell.alpha = ((point.y * 100) / tableView.bounds.maxY) / 100
    }
}

回答2:

I was looking for the same thing, I ended up making my own and I thought I'd share it:

func scrollViewDidScroll(_ scrollView: UIScrollView) {

    let cellCount = tableView.visibleCells.count
    let alphaInterval:CGFloat = 1.0 / CGFloat(cellCount / 2)

    for (index,cell) in (tableView.visibleCells as [UITableViewCell]).enumerated() {

        if index < cellCount / 2 {
            cell.alpha = CGFloat(index) * alphaInterval
        } else {
            cell.alpha = CGFloat(cellCount - index) * (alphaInterval)
        }
    }
}

and here is the cell:

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = UITableViewCell()
    cell.textLabel?.text = countries[indexPath.row].uppercased()
    cell.textLabel?.textColor = .white
    cell.backgroundColor = .clear
    cell.alpha = 0.25

    UIView.animate(withDuration: 0.5, animations: {
        cell.alpha = 1 
    })

    return cell
}

Ends up looking like this: