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