上篇对于UICollectionView默认选中cell采取的是每个cell分别对应一个标识,也就代表着废除了UICollectionView的重用机制。对于较少的数据情况是可以的,但是对于数据比较大,就会造成性能问题。
于是思考在UICollectionView重用机制下,设置默认选中的cell,大致思路就是在cell被选中的时候设置一个selectIndexPath记录下来,在cell被取消选中的时候也用DeselectIndexPath记录下来,除了在cell被选中和取消选中的时候处理,还要在cell被赋值数据和cell即将出现的时候设置。
在为CollectionView设置完数据之后,设置第0个cell被选中:
#pragma mark 设置collectionView的数据 - (void)setupCollectionViewData { for (int i = 0; i < 20; i++) { [self.dataArrayM addObject:[NSString stringWithFormat:@"第%d个cell",i]]; } [self.testCollectionView reloadData]; NSIndexPath *indexPath = [NSIndexPath indexPathForRow:0 inSection:0]; [self.testCollectionView selectItemAtIndexPath:indexPath animated:NO scrollPosition:UICollectionViewScrollPositionNone]; [self collectionView:self.testCollectionView didSelectItemAtIndexPath:indexPath]; }
在viewDidLoad中为seleceIndex设置初试值,并在collectionView选中的方法中,赋值:
- (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib. self.selectIndexPath = [NSIndexPath indexPathForRow:0 inSection:0]; [self setupUICollectionView]; // 设置collectionView的数据 [self setupCollectionViewData]; }
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath { self.selectIndexPath = indexPath; LBCollectionViewCell *cell = (LBCollectionViewCell *)[collectionView cellForItemAtIndexPath:indexPath]; [cell setBackgroundColor:[UIColor greenColor]]; [cell.nameLabel setTextColor:[UIColor redColor]]; }
在collectionView取消选中的代理方法中,为DeselectIndexPath赋值:
- (void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndexPath:(NSIndexPath *)indexPath { self.DeselectIndexpath = indexPath; LBCollectionViewCell *cell = (LBCollectionViewCell *)[collectionView cellForItemAtIndexPath:indexPath]; if (cell == nil) { // 如果重用之后拿不到cell,就直接返回 return; } [cell setBackgroundColor:[UIColor grayColor]]; [cell.nameLabel setTextColor:[UIColor blackColor]]; }
在cell赋值的数据源方法中,设置cell的选中的样式:
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath { LBCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:cellId forIndexPath:indexPath]; [cell.nameLabel setText:self.dataArrayM[indexPath.row]]; if ([self.selectIndexPath isEqual:indexPath]) { [cell setBackgroundColor:[UIColor greenColor]]; [cell.nameLabel setTextColor:[UIColor redColor]]; } else { [cell setBackgroundColor:[UIColor grayColor]]; [cell.nameLabel setTextColor:[UIColor blackColor]]; } return cell; }
在cell出现正在展示的代理方法中再设置选中和未选中的样式:
- (void)collectionView:(UICollectionView *)collectionView didEndDisplayingCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath { LBCollectionViewCell *LBcell = (LBCollectionViewCell *)cell; if (self.DeselectIndexpath && [self.DeselectIndexpath isEqual:indexPath]) { [LBcell setBackgroundColor:[UIColor grayColor]]; [LBcell.nameLabel setTextColor:[UIColor blackColor]]; } if ([self.selectIndexPath isEqual:indexPath]) { [LBcell setBackgroundColor: