删除子视图然后将其重新添加 [英] Removing a subview then adding it back

问题描述

我有一个带有渐变子视图的 UICollectionViewCell 。
在我的视图控制器中，我有一些按钮依次对CoreData进行排序，然后对 UICollectionView 上的 reloadData（）进行排序。
为了避免一次又一次绘制渐变子视图（就像过去那样），我在 prepareForReuse中实现了 removeFromSuperview（） （）。
在那里，我还实现了一个跟踪梯度存在的标记，因此当单元加载时我仍然添加新的梯度。
但是，删除渐变后，我的 willMove（toSuperview：）不起作用，并且没有出现渐变视图。
我的逻辑怎么了？

I have a UICollectionViewCell with a gradient subview. In my view controller, I have buttons that are sorting CoreData and then reloadData() on the UICollectionView. To avoid my gradient subview to be drawn again and again (as it happened in the past), I implement removeFromSuperview() in prepareForReuse(). There I also implement a flag that keeps track of gradient existence so I still add a new gradient when cell is load. However after removing the gradient, my willMove(toSuperview: ) doesn't work, and gradient view doesn't appear. What's wrong with my logic?

class CollectionCell: UICollectionViewCell {

@IBOutlet weak var mealImg: UIImageView!
@IBOutlet weak var mealTitleLbl: UILabel!
@IBOutlet weak var gradientView: UIView!

var gradientWasRemoved = false

func configureCell(meal: Meal) {
    mealTitleLbl.text = meal.title

    let img = meal.getMealImage()
    mealImg.image = img

    addGradient()    
}

  func addGradient () {
    let gradient = CAGradientLayer()
    gradient.frame = gradientView.bounds
    let topColor = UIColor(red:0.07, green:0.07, blue:0.07, alpha:1)
    let botomColor = UIColor.clear
    gradient.colors = [topColor.cgColor, botomColor.cgColor]
    gradientView.layer.insertSublayer(gradient, at: 0)

    if gradientWasRemoved == true {
        gradientView.willMove(toSuperview: self)
    } 
}

override func prepareForReuse() {
    super.prepareForReuse()

   gradientView.removeFromSuperview()
   gradientWasRemoved = true
}
}

推荐答案

我能够通过以下方式修复逻辑。
在UICollectionViewCell类中：

I was able to fix the logic with following. In UICollectionViewCell class:

import UIKit

class CollectionCell: UICollectionViewCell {

@IBOutlet weak var mealImg: UIImageView!
@IBOutlet weak var gradientView: UIView!

@IBOutlet weak var mealTitleLbl: UILabel!

var gradientWasRemoved = false

func configureCell(meal: Meal) {
    mealTitleLbl.text = meal.title

    let img = meal.getMealImage()
    mealImg.image = img

    addGradient()
}

  func addGradient () {

    let gradient = CAGradientLayer()
    gradient.frame = gradientView.bounds
    let topColor = UIColor(red:0.07, green:0.07, blue:0.07, alpha:1)
    let botomColor = UIColor.clear
    gradient.colors = [topColor.cgColor, botomColor.cgColor]

    if gradientWasRemoved == false {
    gradientView.layer.insertSublayer(gradient, at: 0)
    } else if gradientWasRemoved == true {
        self.addSubview(gradientView)
    }
}

override func prepareForReuse() {
    super.prepareForReuse()

   gradientView.removeFromSuperview()
   gradientWasRemoved = true
}

}

在 prepareForReus中e（）我没有删除 gradientView ，而是将其从Superview中删除了。我在那里设置了将其删除的标志。
因为我没有 nil 我的 gradientView ，所以我能够运行 addGradient （）并访问 gradientView.bounds 来创建新的 CGGradientLayer 。
在向 gradientView 添加新图层之前，我执行了 if 检查。如果确实删除了 gradientView ，那么我们就不会添加新的 CGGradientLayer ，而只需添加我们的 back 。
这样，我们只将 CGGradientLayer 添加到我们的gradientView中一次。

In prepareForReuse( ) I didn't delete gradientView, I removed it from the Superview. I set the flag there that it was removed. Since I didn't nil my gradientView i was able to run addGradient() and access gradientView.bounds for creation of new CGGradientLayer. Right before adding a new layer to gradientView, I performed if check. If we did remove gradientView then we don't add a new CGGradientLayer but simply put our gradientView back. This way we add CGGradientLayer to our gradientView only once.

我了解到，通过从Superview中删除视图，这些视图仍然有效并且可以进行编辑。

I learned that by removing views from Superview they are still alive and can be edited.

感谢@Luis和@LeoDabus。

Thank you @Luis and @LeoDabus for your contribution.

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