上篇對於UICollectionView預設選中cell採取的是每個cell分別對應一個標識,也就代表著廢除了UICollectionView的重用機制。對於較少的數據情況是可以的,但是對於數據比較大,就會造成性能問題。 於是思考在UICollectionView重用機制下,設置預設選中的cell, ...
上篇對於UICollectionView預設選中cell採取的是每個cell分別對應一個標識,也就代表著廢除了UICollectionView的重用機制。對於較少的數據情況是可以的,但是對於數據比較大,就會造成性能問題。
於是思考在UICollectionView重用機制下,設置預設選中的cell,大致思路就是在cell被選中的時候設置一個selectIndexPath記錄下來,在cell被取消選中的時候也用DeselectIndexPath記錄下來,除了在cell被選中和取消選中的時候處理,還要在cell被賦值數據和cell即將出現的時候設置。
在為CollectionView設置完數據之後,設置第0個cell被選中:
#pragma mark 設置collectionView的數據 - (void)setupCollectionViewData { for (int i = 0; i < 20; i++) { [self.dataArrayM addObject:[NSString stringWithFormat:@"第%d個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中為seleceIndex設置初試值,併在collectionView選中的方法中,賦值:
- (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]; // 設置collectionView的數據 [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取消選中的代理方法中,為DeselectIndexPath賦值:
- (void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndexPath:(NSIndexPath *)indexPath { self.DeselectIndexpath = indexPath; LBCollectionViewCell *cell = (LBCollectionViewCell *)[collectionView cellForItemAtIndexPath:indexPath]; if (cell == nil) { // 如果重用之後拿不到cell,就直接返回 return; } [cell setBackgroundColor:[UIColor grayColor]]; [cell.nameLabel setTextColor:[UIColor blackColor]]; }
在cell賦值的數據源方法中,設置cell的選中的樣式:
- (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出現正在展示的代理方法中再設置選中和未選中的樣式:
- (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]]; } }
完整代碼如下:
// // 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> // 數據數組 @property (nonatomic, strong) NSMutableArray *dataArrayM; @property (nonatomic, weak) UICollectionView *testCollectionView; // 選中cell的indexPath @property (nonatomic, strong) NSIndexPath *selectIndexPath; // 取消選中的cell,防止由於重用,在取消選中的代理方法中沒有設置 @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]; // 設置collectionView的數據 [self setupCollectionViewData]; } #pragma mark - private Method #pragma mark 設置collectionView的數據 - (void)setupCollectionViewData { for (int i = 0; i < 20; i++) { [self.dataArrayM addObject:[NSString stringWithFormat:@"第%d個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 { // 設置uicollectionView樣式 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) { // 如果重用之後拿不到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 - 懶載入 - (NSMutableArray *)dataArrayM { if (!_dataArrayM) { _dataArrayM = [NSMutableArray array]; } return _dataArrayM; } @end
github地址: https://github.com/OLeGeB/selectCollectionViewCell.git