swift - 在自定义 UICollectionViewCell 中将叠加层添加到 UIImageView

Question

我有一个带有一些属性的自定义 UICollectionViewCell 类:

class SimpleCollectionCell: UICollectionViewCell {

    @IBOutlet weak var title_more: UILabel!

    @IBOutlet weak var image_more: UIImageView!

    @IBOutlet weak var title: UILabel!

    @IBOutlet weak var distance: UILabel!

    @IBOutlet weak var activity: UIImageView!

}

我填充数据的方法是这样的:

override func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {

    let cell = collectionView.dequeueReusableCellWithReuseIdentifier("cell", forIndexPath: indexPath) as! SimpleCollectionCell

    var place = Place()

    // set the current place
    place = Places[indexPath.row]

    // set the label
    cell.title.text = place.title

    // setup url
    let url = NSURL(string: currentThing.imageUrl!)

    // set the cell image
    cell.activity.hnk_setImageFromURL(url!)

    return cell

}

单元格按应有的方式呈现并显示:

我的问题是如何让图像变暗？

我尝试在 cellForItemAtIndexPath 方法的底部添加以下代码，但是当您滚动时它会变暗，因为它会不断添加更多 subview !

// Create a subview which will add an overlay effect on image view
let overlay: UIView = UIView(frame: CGRectMake(0, 0, cell.activity.frame.size.width, cell.activity.frame.size.height))
    overlay.backgroundColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.3);

// Add the subview to the UIImageView
cell.activity.addSubview(overlay)

Answer 1

一个快速的解决方案是检查是否已将叠加层添加到单元格中，如果是，则不添加另一个叠加层。

使用标签:

if cell.activity.viewWithTag(99) == nil {
    // Create a subview which will add an overlay effect on image view
    let overlay = UIView(frame: CGRect(x: 0, y: 0, width: cell.frame.size.width, height: cell.frame.size.height))
    overlay.backgroundColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.3);
    overlay.tag = 99

    // Add the subview to the UIImageView
    cell.activity.addSubview(overlay)
}

或者只是从单元格内创建叠加层。