在第一次加载视图时预选择/突出显示 UICollectionViewCell
Posted
技术标签:
【中文标题】在第一次加载视图时预选择/突出显示 UICollectionViewCell【英文标题】：pre select/highlight UICollectionViewCell on first load of view 【发布时间】：2015-04-23 14:34:26 【问题描述】：我试图在 UICollectionView 中预选第一个对象/UICollectionViewCell？我试过了：
self.dateCollectionView.allowsMultipleSelection=NO;
[self.dateCollectionView selectItemAtIndexPath:0 animated:YES scrollPosition:UICollectionViewScrollPositionLeft];
[self collectionView:self.dateCollectionView didSelectItemAtIndexPath:0];
[self.dateCollectionView reloadData];
在viewDidLoad.
这是我的UICollectionView 方法；
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
return self.titles.count;
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
UICollectionViewCell * cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];
cell.backgroundColor= [UIColor clearColor];
UILabel * dateLabel = (UILabel *)[cell viewWithTag:1];
UILabel * subText = (UILabel *)[cell viewWithTag:2];
subText.text=self.titles[indexPath.row];
subText.adjustsFontSizeToFitWidth=YES;
if (cell.selected)
cell.backgroundColor = [UIColor blueColor]; // highlight selection
else
cell.backgroundColor = [UIColor redColor]; // Default color
return cell;
-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
UICollectionViewCell *datasetCell =[collectionView cellForItemAtIndexPath:indexPath];
datasetCell.backgroundColor = [UIColor blueColor]; // highlight selection
-(void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndexPath:(NSIndexPath *)indexPath
UICollectionViewCell *datasetCell =[collectionView cellForItemAtIndexPath:indexPath];
datasetCell.backgroundColor = [UIColor redColor]; // Default color
- (BOOL)collectionView:(UICollectionView *)collectionView
shouldHighlightItemAtIndexPath:(NSIndexPath *)indexPath
return YES;
- (BOOL)collectionView:(UICollectionView *)collectionView
shouldSelectItemAtIndexPath:(NSIndexPath *)indexPath;
return YES;
【问题讨论】：
【参考方案1】：在viewDidAppear:
NSIndexPath *indexPathForFirstRow = [NSIndexPath indexPathForRow:0 inSection:0];
[self.dateCollectionView selectItemAtIndexPath:indexPathForFirstRow animated:NO scrollPosition:UICollectionViewScrollPositionNone];
[self collectionView:self.dateCollectionView didSelectItemAtIndexPath:indexPathForFirstRow];
【讨论】：
【参考方案2】：对于 Swift 3.0.1 你可以试试这个：
self.collectionView.selectItem(at: indexPath, animated: true, scrollPosition: [])
或
self.collectionView.selectItem(at: indexPath, animated: true, scrollPosition: UICollectionViewScrollPosition(rawValue: 0))
对于 Objective-C 你可以试试这个：
self.collectionView selectItemAtIndexPath:indexPath animated:YES scrollPosition:UICollectionViewScrollPositionNone];
注意：你应该在viewDidAppear
中使用它【讨论】：
【参考方案3】：对于 swift 3
在这个重载collectionView(UICollectionView, IndexPath)中使用collectionView.selectItem
这是我的代码，在此代码中，我预先选择了带有indexPath.row = 0 的行
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell
let cell = ScenarioCollectionView.dequeueReusableCell(withReuseIdentifier: "ReuseScenarioCollectionViewCell", for: indexPath as IndexPath) as! ScenarioCollectionViewCell
if (indexPath.row == 0)
collectionView.selectItem(at: indexPath, animated: true, scrollPosition: UICollectionViewScrollPosition.centeredHorizontally)
cell.layer.borderColor=UIColor.gray.cgColor
else
cell.layer.borderColor=UIColor.white.cgColor
return cell
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath)
let cell = collectionView.cellForItem(at: indexPath)
cell?.layer.borderColor = UIColor.gray.cgColor
func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath)
let cell = collectionView.cellForItem(at: indexPath as IndexPath)
cell?.layer.borderColor = UIColor.white.cgColor
collectionView.deselectItem(at: indexPath, animated: true)
【讨论】：
【参考方案4】：我通过子类化UICollectionView 并在layoutSubviews 中选择需要的项目解决了这个问题：
class InitialSelectionCollectionView: UICollectionView
var initialSetupPerformed: Bool = false
var initialSelectedIndexPath: IndexPath!
override func layoutSubviews()
super.layoutSubviews()
if !initialSetupPerformed && initialSelectedIndex != nil
selectItem(at: initialSelectedIndexPath, animated: false, scrollPosition: .centeredHorizontally)
initialSetupPerformed = true
然后，当您初始化自定义集合视图时，只需将需要的 IndexPath 设置为 initialSelectedIndexPath
【讨论】：
【参考方案5】：对我来说，将其放入 viewDidAppear: 会导致第二次选择，因此用户将看到两种状态（即未选择和已选择）。
为了避免这种情况，我把它放在viewWillAppear: 中，并像魅力一样工作
override func viewWillAppear(_ animated: Bool)
let selectedIndexPath = IndexPath(item: 0, section: 0)
collectionView.selectItem(at: selectedIndexPath, animated: false, scrollPosition: .left)
【讨论】：
【参考方案6】：对于 Swift 3：
override func viewDidAppear(_ animated: Bool)
super.viewDidAppear(animated)
//auto selected 1st item
let indexPathForFirstRow = IndexPath(row: 0, section: 0)
self.collectionView?.selectItem(at: indexPathForFirstRow, animated: true, scrollPosition: .top)
【讨论】：
【参考方案7】： [self.collectionView reloadData];
[self.collectionView layoutIfNeeded]; //important
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:0];
[self.collectionView selectItemAtIndexPath:indexPath animated:NO scrollPosition:UICollectionViewScrollPositionNone];
[self collectionView:self.collectionView didSelectItemAtIndexPath:indexPath];
【讨论】：
layoutIfNeeded 拯救了我的一天！【参考方案8】：
用于初始选择单元格的快速代码
func selectinitialCell()
let cell = venueTypeCollectionView.cellForItemAtIndexPath(NSIndexPath(forItem: 0, inSection: 0)) as! SearchTypeCollectionViewCell
self.indexPathOfSelectedItem = NSIndexPath(forItem: 0, inSection: 0)
cell.venueType.textColor = UIColor.whiteColor()
cell.selected = true
但这不会调用didSelectItemAtIndexPath、didDeselectItemAtIndexPath等委托函数。
【讨论】：
【参考方案9】： Here is full code link就我而言。我通过带有Generic types 的UICollectionView 类的子类解决了它
// ******************************************
//
// MARK: - Config injection, Extend whatever you want
//
// ******************************************
struct CCCollectionViewConfig
var itemSize: CGSize?
var minimumInteritemSpacing: CGFloat?
var minimumLineSpacing: CGFloat?
var allowsDefaultSelection: Bool = true
// ******************************************
//
// MARK: - Generic CCCollectionView
//
// ******************************************
final class CCCollectionView<T, Cell: UICollectionViewCell>: UICollectionView, UICollectionViewDataSource, UICollectionViewDelegate
typealias SelectHandler = (T, IndexPath?) -> Void
typealias CellConfigure = (Cell, T) -> Void
var contents: [T] = []
didSet
DispatchQueue.main.async
self.reloadData()
self.selectedIndexPath = IndexPath(item: (self.config.allowsDefaultSelection) ? 0 : -1, section: 0)
var configure: CellConfigure
var selectHandler: SelectHandler
var selectedIndexPath: IndexPath
private var config: CCCollectionViewConfig
private let identifier = "identifier"
init(contents: [T], config: CCCollectionViewConfig, configure: @escaping CellConfigure, selectHandler: @escaping SelectHandler)
self.config = config
self.contents = contents
self.configure = configure
self.selectHandler = selectHandler
self.selectedIndexPath = IndexPath(item: (config.allowsDefaultSelection) ? 0 : -1, section: 0)
let layout = UICollectionViewFlowLayout()
if let size = config.itemSize
layout.itemSize = size
layout.minimumInteritemSpacing = config.minimumInteritemSpacing ?? 0
layout.minimumLineSpacing = config.minimumLineSpacing ?? 0
layout.scrollDirection = .vertical
layout.sectionInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
super.init(frame: .zero, collectionViewLayout: layout)
setup()
required init?(coder aDecoder: NSCoder)
fatalError("init(coder:) has not been implemented")
private func setup()
register(Cell.self, forCellWithReuseIdentifier: identifier)
super.delegate = self
super.dataSource = self
allowsMultipleSelection = false
isScrollEnabled = false
backgroundColor = .clear
// ******************************************
//
// MARK: - UICollectionViewDataSource, UICollectionViewDelegate
//
// ******************************************
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int
return contents.count
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: identifier, for: indexPath) as! Cell
cell.isSelected = (selectedIndexPath == indexPath)
let content = contents[indexPath.row]
configure(cell, content)
return cell
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath)
let content = contents[indexPath.row]
selectHandler(content, indexPath)
/// If selected item is equal to current selected item, ignore it
if selectedIndexPath == indexPath
return
/// Handle selected cell
let selectedCell = collectionView.cellForItem(at: indexPath)
selectedCell?.isSelected = true
/// Handle deselected cell
let deselectItem = collectionView.cellForItem(at: selectedIndexPath)
deselectItem?.isSelected = false
selectedIndexPath = indexPath
// ******************************************
//
// MARK: - CollectionViewCell
//
// ******************************************
final class CCCollectionViewCell: UICollectionViewCell
var title: String = ""
didSet
titleLabel.text = title
private let titleLabel: UILabel =
let label = UILabel()
return label
()
var _isSelected: Bool = false
override var isSelected: Bool
get
return _isSelected
set(newValue)
_isSelected = newValue
updateSelection()
private func updateSelection() -> Void
contentView.layer.borderColor = isSelected ? UIColor.red.cgColor : UIColor.green.cgColor
override init(frame: CGRect)
super.init(frame: frame)
contentView.addSubview(titleLabel)
contentView.layer.cornerRadius = 2.0
contentView.layer.borderWidth = 2.0
required init?(coder aDecoder: NSCoder)
fatalError("init(coder:) has not been implemented")
然后在你的 ViewController 中使用它
private let fakeContents = Array(repeating: "123123", count: 40)
/// Collection View Config
private lazy var config: CCCollectionViewConfig =
return CCCollectionViewConfig(itemSize: CGSize(width: 100, height: 30),
minimumInteritemSpacing: 4.0,
minimumLineSpacing: 4.0)
()
/// Collection View Config
private lazy var collectionView: CCCollectionView<String, CCCollectionViewCell> =
let cv = CCCollectionView<String, CCCollectionViewCell>(contents: fakeContents, config: config, configure: (cell: CCCollectionViewCell, content) in
cell.title = content
) [weak self] (content, indexPath) in
guard let self = self else return
guard let row = indexPath?.row else return
return cv
()
【讨论】：
以上是关于在第一次加载视图时预选择/突出显示 UICollectionViewCell的主要内容，如果未能解决你的问题，请参考以下文章
在应用程序启动时预加载 UITabBar 选项卡时出现问题（崩溃）