在自定义到的UIImageView添加覆盖UICollectionViewCell

Question

我有几个属性的自定义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! 

} 

我来填充数据的方法是这样：

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 

} 

细胞呈现为它应该与显示为这样：

我的问题是如何让图像变暗？

我试图添加下面的代码在cellForItemAtIndexPath方法的底部，但它会变得越来越黑，因为它不断添加更多的子视图！

// 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

一个快速解决方案是检查是否已经添加叠加到单元格，如果没有添加另一个。

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) 
} 

或者刚刚从单元格中创建的覆盖。