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 = ; i < ; i++) {
[self.dataArrayM addObject:[NSString stringWithFormat:@"第%d个cell",i]];
} [self.testCollectionView reloadData]; NSIndexPath *indexPath = [NSIndexPath indexPathForRow: inSection:]; [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: inSection:];
[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: inSection:]; [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 = ; i < ; i++) {
[self.dataArrayM addObject:[NSString stringWithFormat:@"第%d个cell",i]];
} [self.testCollectionView reloadData]; NSIndexPath *indexPath = [NSIndexPath indexPathForRow: inSection:]; [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 = ;
flowLayout.minimumInteritemSpacing = ;
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 ;
} - (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(, );
} - (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