UICollectionView设置首个cell默认选中(二)
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:[UIColor greenColor]]; [LBcell.nameLabel setTextColor:[UIColor redColor]]; } }
完整代码如下：
// // ViewController.m // testSelect // // Created by 李江波 on 2019/4/22. // Copyright © 2019年 jinxiaofu. All rights reserved. // #import "ViewController.h" #import "LBCollectionViewCell.h" static NSString *const cellId = @"cellId"; @interface ViewController ()<UICollectionViewDelegate, UICollectionViewDataSource> // 数据数组 @property (nonatomic, strong) NSMutableArray *dataArrayM; @property (nonatomic, weak) UICollectionView *testCollectionView; // 选中cell的indexPath @property (nonatomic, strong) NSIndexPath *selectIndexPath; // 取消选中的cell，防止由于重用，在取消选中的代理方法中没有设置 @property (nonatomic, strong) NSIndexPath *DeselectIndexpath; @end @implementation ViewController - (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]; } #pragma mark - private Method #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]; } #pragma mark - setupUI #pragma mark setupUICollectionView - (void)setupUICollectionView { // 设置uicollectionView样式 UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init]; flowLayout.minimumLineSpacing = 15; flowLayout.minimumInteritemSpacing = 15; flowLayout.scrollDirection = UICollectionViewScrollDirectionHorizontal; UICollectionView *testCollectionView = [[UICollectionView alloc] initWithFrame:self.view.bounds collectionViewLayout:flowLayout]; [testCollectionView registerClass:[LBCollectionViewCell class] forCellWithReuseIdentifier:cellId]; testCollectionView.delegate = self; testCollectionView.dataSource = self; [testCollectionView setBackgroundColor:[UIColor whiteColor]]; [self.view addSubview:testCollectionView]; self.testCollectionView = testCollectionView; } #pragma mark - UICollectionViewDatasource - (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView { return 1; } - (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section { return [self.dataArrayM count]; } - (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; } #pragma mark - UICollectionViewDelegate - (CGSize) collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath { return CGSizeMake(150, 150); } - (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]]; } - (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]]; } - (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:[UIColor greenColor]]; [LBcell.nameLabel setTextColor:[UIColor redColor]]; } } #pragma mark - 懒加载 - (NSMutableArray *)dataArrayM { if (!_dataArrayM) { _dataArrayM = [NSMutableArray array]; } return _dataArrayM; } @end
github地址: https://github.com/OLeGeB/selectCollectionViewCell.git
