[英]how to prevent cell reuse of uicollectionview
我使用UICollectionView并引用此链接实现scroll table view Fixed single column and row
,如下图所示。
但是当我想添加shadow
属性时,它显示为混乱。
我认为原因是我在渲染可视视图时重用了cell
,但是我不知道如何解决它:(
在下面提供我的代码,谢谢您的宝贵时间!
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
}
}
您正在为某个节/行指定自定义项,在其他情况下,您只需设置文本即可。 您应该在else条件中指定所需的/默认的自定义。 考虑代码的这一部分
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
}
您已在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,则不会遇到现在遇到的问题。 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
}
如果在所有条件检查中都正确重置了所有内容,则不会出现此问题。
当行等于0时设置阴影:
if indexPath.row == 0 {...}
但是如果该行不等于零,则在设置阴影后,视图可以重用该单元格。 解决方案是在row不为0时重置阴影,在您的代码中您可以执行以下操作(请参见todo):
if indexPath.row == 0 { // Set up shadow here
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
//TODO: Remove the shadow here
}
如果您想每次在单元格出现时都保存单元格设置,则应设置方法“ func collectionView(collectionView:UICollectionView,cellForItemAtIndexPath indexPath:NSIndexPath)-> UICollectionViewCell”的所有可能条件。仅当您数据或项目很少。
在Objective-C中,但在Swift中,逻辑应该相同并且不难翻译。
在RNCollectionCell
。
//These enums may have a better nam, I agree
typedef enum : NSUInteger {
RNCollectionCellStyleColumnTitle,
RNCollectionCellStyleColumnValue,
RNCollectionCellStyleRowTitle,
RNCollectionCellStyleUpperLeftCorner,
} RNCollectionCellStyle;
-(void)titleIt:(NSString *)title forStyle:(RNCollectionCellStyle)style forSection:(NSUInteger)section
{
self.textLabel.textColor = [UIColor blackColor]; //Since it's always the same could be done elsewhere once for all.
//Note I didn't check completely if the case were good, and I didn't add the background color logic, but it should be done here too.
switch (style)
{
case RNCollectionCellStyleColumnTitle:
{
self.textLabel.font = [UIFont systemFontOfSize:12];
self.layer.shadowOffset = CGSizeMake(3, 3);
self.layer.shadowOpacity = 0.7;
self.layer.shadowRadius = 2;
}
break;
case RNCollectionCellStyleColumnValue:
{
self.textLabel.font = [UIFont systemFontOfSize:12];
self.layer.shadowOffset = CGSizeZero;
self.layer.shadowOpacity = 0;
self.layer.shadowRadius = 0;
}
break;
case RNCollectionCellStyleRowTitle:
{
self.textLabel.font = [UIFont systemFontOfSize:14];
self.layer.shadowOffset = CGSizeZero;
self.layer.shadowOpacity = 0;
self.layer.shadowRadius = 0;
}
break;
case RNCollectionCellStyleUpperLeftCorner:
{
self.textLabel.font = [UIFont systemFontOfSize:16];
self.layer.shadowOffset = CGSizeZero;
self.layer.shadowOpacity = 0;
self.layer.shadowRadius = 0;
}
break;
default:
break;
}
self.textLabel.text = title;
}
-(void)prepareForReuse
{
[super prepareForReuse];
self.layer.shadowOffset = CGSizeZero;
self.layer.shadowOpacity = 0;
self.layer.shadowRadius = 0;
}
在RNCollection
:
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(nonnull NSIndexPath *)indexPath
{
RNCollectionCell *contentCell = [collectionView dequeueReusableCellWithReuseIdentifier: contentCellIdentifier forIndexPath:indexPath];
//Here check what style you need to do
//Also, you seems to always do dataSource[indexPath.section][indexPath.row], you just use the "if test values".
[contentCell titleIt:dataSource[indexPath.section][indexPath.row]
forStyle:RNCollectionCellStyleColumnTitle
forSection:[indexPath section]];
return contentCell;
}
如前所述,我没有根据您的需要检查所有案例是否正确。 但是,您并没有“防止单元的重用”,而是对其进行了优化。 您需要在重用之前或设置值时“重置”值。 从理论上讲,在prepareForReuse
完成的工作应该足够了,您不必不必“重置” switch
的图层效果,但是老实说我没有检查它。
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