Question

获取不可见的单元格可能会也可能不会获取单元格，即使索引位置不为空。

总结：我已经尝试在shouldSelectItemAt函数中选择和取消选择逻辑。选择顺利。但是在选择新单元时，需要取消选择先前选择的单元。当我使用自定义集合视图布局时，我怀疑由于单元格的可重用性而出现问题。

代码：

func collectionView(_ collectionView: UICollectionView, shouldSelectItemAt indexPath: IndexPath) -> Bool {
if(collectionView == customContentCollectionView){
let cell:MyContentCell = collectionView.cellForItem(at: indexPath)! as! MyCollectionViewController.MyContentCell

// DESELECTION CODE
if(previouslySelectedIndex != nil){
                                    // following line is error prone (executes but may or may not fetch the cell, sometimes deselect sometimes doesnt)
                                    let prevCell = try collectionView.cellForItem(at: previouslySelectedIndex) as? MyCollectionViewController.MyContentCell

                                    // Also tried with this following (executes but fails sometimes, in case not fetching the cell)
                                    //let prevCell = try collectionView.cellForItem(at: previouslySelectedIndex)! as! MyCollectionViewController.MyContentCell

                                    // Tried this one as well, fetching the previously selected cell using datasource, not directly from collection view
                                    // let prevCell = customContentCollectionView.dataSource?.collectionView(collectionView, cellForItemAt: previouslySelectedIndex) as? MyCollectionViewController.MyContentCell

                                    prevCell?.shapeLayer.strokeColor = bubbleBorder.cgColor
                                    prevCell?.shapeLayer.fillColor = bubbleFill.cgColor
                                    prevCell?.shapeLayer.shadowOpacity = 0.0
                                    prevCell?.labelCount.textColor = bubbleBorder
}

// SELECTION CODE HERE GOES PRETTY WELL
...
previouslySelectedIndex = indexPath
}

N.B。：我正在使用CustomUICollectionViewFlowLayout，我只需要使用shouldSelectItemAt函数。没有其他功能可供选择和取消选择。

Answer 1

let prevCell = try collectionView.cellForItem(at: previouslySelectedIndex) as? MyCollectionViewController.MyContentCell

返回nil，因为如果用户滚动了collectionView单元格可能已经被重用于其他一些indexPath，那么返回nil。

所以你不应该要求来自collectionView的单元格，而应该询问数据源

let cell = self.collectionView?.dataSource?.collectionView(self.collectionView!, cellForItemAt: IndexPath(row: 0, section: 0))

其他方法是在重用之前使用prepareForReuse重置单元状态。 prepareForReuse听起来更合理的解决方案：）

修改

第二个想法虽然上面的代码将返回单元格，更新未加载/重用的单元格的UI将导致不利影响。相反，只有当单元格可用时，您才可以在shouldSelectItemAt更新取消选择的单元格的UI

func collectionView(_ collectionView: UICollectionView, shouldSelectItemAt indexPath: IndexPath) -> Bool { if(collectionView == customContentCollectionView){ let cell:MyContentCell = collectionView.cellForItem(at: indexPath)! as! MyCollectionViewController.MyContentCell // DESELECTION CODE if(previouslySelectedIndex != nil){ // following line is error prone (executes but may or may not fetch the cell, sometimes deselect sometimes doesnt) if let prevCell = try collectionView.cellForItem(at: previouslySelectedIndex) as? MyCollectionViewController.MyContentCell { // Also tried with this following (executes but fails sometimes, in case not fetching the cell) //let prevCell = try collectionView.cellForItem(at: previouslySelectedIndex)! as! MyCollectionViewController.MyContentCell // Tried this one as well, fetching the previously selected cell using datasource, not directly from collection view // let prevCell = customContentCollectionView.dataSource?.collectionView(collectionView, cellForItemAt: previouslySelectedIndex) as? MyCollectionViewController.MyContentCell prevCell?.shapeLayer.strokeColor = bubbleBorder.cgColor prevCell?.shapeLayer.fillColor = bubbleFill.cgColor prevCell?.shapeLayer.shadowOpacity = 0.0 prevCell?.labelCount.textColor = bubbleBorder } } // SELECTION CODE HERE GOES PRETTY WELL previouslySelectedIndex = indexPath } }

如果在上面添加，则应注意确保更新单元格的UI，以便仅在可用时才取消选择。

现在在单元格中实现prepareForReuse

override func prepareForReuse() { //reset all the fields of cell self.shapeLayer.strokeColor = bubbleBorder.cgColor self.shapeLayer.fillColor = bubbleFill.cgColor self.shapeLayer.shadowOpacity = 0.0 self.labelCount.textColor = bubbleBorder }

最后在cellForItemAtIndexPath

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell { //your code to create cell n all if(indexPath == previouslySelectedIndex) { //your code to select the cell } return cell }

希望这有帮助

如何在自定义布局集合视图中取消选择不可见单元格？

1 个答案: