ios - 如何防止 uicollectionview 的单元格重用

Question

我使用 UICollectionView 并引用 this link实现 滚动 TableView 固定单列和单行，如下图所示。

但是当我想添加shadow属性时，它显示的很乱。

我认为原因是我在渲染视觉 View 时重用了cell，但我不知道如何修复它:(

---

在下面提供我的代码，感谢您的宝贵时间!

import Foundation
import SwiftyJSON


@objc(RNCollection)
class RNCollection : UICollectionView, UICollectionViewDataSource, UICollectionViewDelegate {

  var contentCellIdentifier = "CellIdentifier"
  var collectionView: UICollectionView!

  static var dataSource = []
  static var sections = 0
  static var rows = 0

  override init(frame: CGRect, collectionViewLayout layout: UICollectionViewLayout) {
    super.init(frame: CGRectZero, collectionViewLayout: RNCollectionLayout())

    self.registerClass(RNCollectionCell.self, forCellWithReuseIdentifier: contentCellIdentifier)
    self.directionalLockEnabled = false
    self.backgroundColor = UIColor.whiteColor()

    self.delegate = self
    self.dataSource = self

    self.frame = frame
  }

  required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }

  func setConfig(config: String!) {
    var json: JSON = nil;
    if let data = config.dataUsingEncoding(NSUTF8StringEncoding) {
      json = JSON(data: data);
    };

    RNCollection.dataSource = json["dataSource"].arrayObject!
    RNCollection.sections = json["sections"].intValue
    RNCollection.rows = json["rows"].intValue
  }

  func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
    let contentCell: RNCollectionCell = collectionView.dequeueReusableCellWithReuseIdentifier(contentCellIdentifier, forIndexPath: indexPath) as! RNCollectionCell

    contentCell.textLabel.textColor = UIColor.blackColor()

    if indexPath.section == 0 {
      contentCell.backgroundColor = UIColor(red: 232/255.0, green: 232/255.0, blue: 232/255.0, alpha: 1.0)

      if indexPath.row == 0 {
        contentCell.textLabel.font = UIFont.systemFontOfSize(16)
        contentCell.textLabel.text = (RNCollection.dataSource[0] as! NSArray)[0] as? String
      } else {
        contentCell.textLabel.font = UIFont.systemFontOfSize(14)
        contentCell.textLabel.text = (RNCollection.dataSource[0] as! NSArray)[indexPath.row] as? String
      }
    } else {
      contentCell.textLabel.font = UIFont.systemFontOfSize(12)
      contentCell.backgroundColor = UIColor.whiteColor()

      if(indexPath.section % 2 == 0) {
        contentCell.backgroundColor = UIColor(red: 234/255.0, green: 234/255.0, blue: 236/255.0, alpha: 1.0)
      }

      if indexPath.row == 0 {
        contentCell.textLabel.text = (RNCollection.dataSource[indexPath.section] as! NSArray)[0] as? String
        contentCell.layer.shadowOffset = CGSize(width: 3, height: 3)
        contentCell.layer.shadowOpacity = 0.7
        contentCell.layer.shadowRadius = 2
      } else {
        contentCell.textLabel.text = (RNCollection.dataSource[indexPath.section] as! NSArray)[indexPath.row] as? String
      }
    }

    return contentCell
  }

  func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return RNCollection.rows
  }

  // MARK - UICollectionViewDataSource
  func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
    return RNCollection.sections
  }

}

Answer 1

您正在为某个部分/行指定您的自定义项，而在您的其他条件下，您只需设置文本。您应该在 else 条件中指定所需/默认的自定义。考虑这部分代码

  if indexPath.row == 0 {
    contentCell.textLabel.text = (RNCollection.dataSource[indexPath.section] as! NSArray)[0] as? String
    contentCell.layer.shadowOffset = CGSize(width: 3, height: 3)
    contentCell.layer.shadowOpacity = 0.7
    contentCell.layer.shadowRadius = 2
  } else {
    contentCell.textLabel.text = (RNCollection.dataSource[indexPath.section] as! NSArray)[indexPath.row] as? String
  }

您在 if 条件中指定了 shadowOffset、shadowOpacity 和 shadowRadius，但在 else 条件中忽略了它们。如果您在 else 条件下指定外观，您将不会遇到现在面临的问题。它应该看起来像这样

  if indexPath.row == 0 {
    contentCell.textLabel.text = (RNCollection.dataSource[indexPath.section] as! NSArray)[0] as? String
    contentCell.layer.shadowOffset = CGSize(width: 3, height: 3)
    contentCell.layer.shadowOpacity = 0.7
    contentCell.layer.shadowRadius = 2
  } else {
    contentCell.textLabel.text = (RNCollection.dataSource[indexPath.section] as! NSArray)[indexPath.row] as? String
contentCell.layer.shadowOffset = 0
    contentCell.layer.shadowOpacity = 0
    contentCell.layer.shadowRadius = 0
  }

如果您在所有条件检查中正确重置所有内容，则不会发生此问题。