UIColletionView性能调研结果

在之前的code review会议中，遗留了两个问题:

一、

1. 复用cell，cell中嵌套子view

2. 全部使用复用cell

   哪种性能更好?

二、

1. cell中的子View，使用addSubView和removeFormSuperView来控制子View显示与隐藏

2. cell中的子View，一次性addSubView，然后使用hidden属性，来控制子view显示与隐藏

   哪种性能更好？

上述是使用文字表述可能理解起来略加困难，我们具体可以参考以下代码。并附上相应代码的视频，可以直观的看出性能的变化情况

一、

1. 复用cell，cell中嵌套子view

   每个UICollectoinViewCell中包含10个子view。

   UICollectoinView 总共返回5000个cell。每个cell的长宽为屏幕的1/3。总共15000个view

   代码表述如下：

​
@implementation ReuseAllView
- (instancetype)initWithFrame:(CGRect)frame {
 if (self = [super initWithFrame:frame]) {
 [self setUpView];
 }
 return self;
}
​
- (void)setUpView {
 NSInteger i = 0;
 CGFloat margin = 10;
 NSInteger count_row = 10;
 CGFloat v_w = (CGRectGetWidth(self.frame) - (count_row - 1)*margin)/count_row;
 for (; i<count_row; i++) {
 UIView *view = [[UIView alloc]initWithFrame:CGRectMake(i*(margin+v_w), 0, v_w, CGRectGetHeight(self.frame))];
 view.backgroundColor = [UIColor blueColor];
 [self.contentView addSubview:view];
 }
}
@end

#import "ViewController.h"
#import "reuseview/ReuseViewCell.h"
#import "reuseview/ReuserCellCell.h"
#import "reuseview/ReuseAllCell.h"
#import "reuseview/ReuseAllView.h"
​
#define UseCell ReuseAllCell
​
@interface ViewController ()<UICollectionViewDelegate,UICollectionViewDataSource>
@property (nonatomic, strong)UICollectionView *colletionView;
@end
​
@implementation ViewController
​
- (void)viewDidLoad {
 [super viewDidLoad];
 [self.view addSubview:self.colletionView];
}
​
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
 return 1;
}
​
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
 return 5000;
}
​
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
 UseCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:NSStringFromClass([UseCell class]) forIndexPath:indexPath];
 if ([cell respondsToSelector:@selector(updateView)]) {
 [cell performSelector:@selector(updateView)];
 }
 return cell;
}
​
- (UICollectionView *)colletionView {
 if (!_colletionView) {
 UICollectionViewFlowLayout *flowlayout = [[UICollectionViewFlowLayout alloc]init];
 flowlayout.scrollDirection = UICollectionViewScrollDirectionVertical;
 flowlayout.minimumLineSpacing = 0.;
 flowlayout.minimumInteritemSpacing = 0.;
 flowlayout.estimatedItemSize = CGSizeZero;
 flowlayout.itemSize = CGSizeMake(self.view.frame.size.width/3, self.view.frame.size.width/3);
 _colletionView = [[UICollectionView alloc]initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height) collectionViewLayout:flowlayout];
 _colletionView.backgroundColor = [UIColor whiteColor];
 [_colletionView registerClass:[UseCell class] forCellWithReuseIdentifier:NSStringFromClass([UseCell class])];
 _colletionView.delegate = self;
 _colletionView.dataSource = self;
 }
 return _colletionView;
}
​
@end

滑动到最底部，再滑动到最顶部，性能反馈如下：

image

2. 全部使用复用cell。

   UIColloctionView返回总共15000个cell。每个cell宽屏幕的1/30。长屏幕的1/3。

   代码表述如下：

    #import "ReuseAllCell.h"
    ​
    @implementation ReuseAllCell
    - (instancetype)initWithFrame:(CGRect)frame {
     if (self = [super initWithFrame:frame]) {
     self.backgroundColor = [UIColor orangeColor];
     }
     return self;
    }
    @end

    #import "ViewController.h"
    #import "reuseview/ReuseViewCell.h"
    #import "reuseview/ReuserCellCell.h"
    #import "reuseview/ReuseAllCell.h"
    #import "reuseview/ReuseAllView.h"
    ​
    #define UseCell ReuseAllCell
    ​
    @interface ViewController ()<UICollectionViewDelegate,UICollectionViewDataSource>
    @property (nonatomic, strong)UICollectionView *colletionView;
    @end
    ​
    @implementation ViewController
    ​
    - (void)viewDidLoad {
     [super viewDidLoad];
     [self.view addSubview:self.colletionView];
    }
    ​
    - (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
     return 1;
    }
    ​
    - (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
     return 5000*3;
    }
    ​
    - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
     UseCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:NSStringFromClass([UseCell class]) forIndexPath:indexPath];
     if ([cell respondsToSelector:@selector(updateView)]) {
     [cell performSelector:@selector(updateView)];
     }
     return cell;
    }
    ​
    - (UICollectionView *)colletionView {
     if (!_colletionView) {
     UICollectionViewFlowLayout *flowlayout = [[UICollectionViewFlowLayout alloc]init];
     flowlayout.scrollDirection = UICollectionViewScrollDirectionVertical;
     flowlayout.minimumLineSpacing = 0.;
     flowlayout.minimumInteritemSpacing = 0.;
     flowlayout.estimatedItemSize = CGSizeZero;
     flowlayout.itemSize = CGSizeMake(self.view.frame.size.width/30, self.view.frame.size.width/3);
     _colletionView = [[UICollectionView alloc]initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height) collectionViewLayout:flowlayout];
     _colletionView.backgroundColor = [UIColor whiteColor];
     [_colletionView registerClass:[UseCell class] forCellWithReuseIdentifier:NSStringFromClass([UseCell class])];
     _colletionView.delegate = self;
     _colletionView.dataSource = self;
     }
     return _colletionView;
    }
    ​
    @end

滑动到最底部，再滑动到最顶部，性能反馈如下：

image

可以从视频上看出：无论从CPU峰值还是，RAM的占用情况，全部复用cell的性能都比复用cell再嵌套view的性能要差一些。

二、

1. cell中的子View，使用addSubView和removeFormSuperView来控制子View显示与隐藏

   UICollectionView总共返回5000个cell。

   其中每个cell中嵌套500个view。

   代码表述如下：

    #import "ReuseViewCell.h"
    @interface ReuseViewCell ()
    @property (nonatomic, strong)NSMutableArray *views;
    @end
    @implementation ReuseViewCell
    - (instancetype)initWithFrame:(CGRect)frame {
     if (self = [super initWithFrame:frame]) {
     self.views = [NSMutableArray array];
     [self setUpView];
     }
     return self;
    }
    ​
    - (void)setUpView {
     if (self.views.count) {
     [self updateView];
     } else {
     for (NSInteger i = 0; i<500; i++) {
     UIView *view = [[UIView alloc]initWithFrame:CGRectMake(0, 0, CGRectGetWidth(self.frame), CGRectGetHeight(self.frame))];
     view.backgroundColor = [UIColor redColor];
     [self.contentView addSubview:view];
     [self.views addObject:view];
     }
     }

    }
    ​
    - (void)updateView {
     [self.views makeObjectsPerformSelector:@selector(removeFromSuperview)];
     for (UIView *view in self.views) {
     [self.contentView addSubview:view];
     }
    }
    @end

滑动到最底部，再滑动到最顶部，性能反馈如下：

image

2. cell中的子View，一次性addSubView，然后使用hidden属性，来控制子view显示与隐藏。

UICollectionView返回5000个cell，每个cell中嵌套500个view。

代码表述如下：

        #import "ReuserCellCell.h"
        @interface ReuserCellCell ()
        ​
        @end
        @implementation ReuserCellCell
        - (instancetype)initWithFrame:(CGRect)frame {
         if (self = [super initWithFrame:frame]) {
         [self setUpView];
         }
         return self;
        }
        ​
        - (void)setUpView {
         if (self.contentView.subviews.count) {
         [self updateView];
         } else {
         for (NSInteger i = 0; i<500; i++) {
         UIView *view = [[UIView alloc]initWithFrame:CGRectMake(0, 0, CGRectGetWidth(self.frame), CGRectGetHeight(self.frame))];
         view.backgroundColor = [UIColor greenColor];
         [self.contentView addSubview:view];
         }
         }
        }
        ​
        - (void)updateView {
         [self.contentView.subviews makeObjectsPerformSelector:@selector(setHidden:) withObject:@(YES)];
         [self.contentView.subviews makeObjectsPerformSelector:@selector(setHidden:) withObject:@(NO)];
        }
        @end

滑动到最底部，再滑动到最顶部，性能反馈如下：

image

从上述结果，可以很明显的看出，第一种方式比第二种方式，无论从cup使用率还是RAM的占用情况，都差了很多，并且，第一种方式，明显造成了页面卡顿。

于此同时，在代码中，第一种方式的写法也会造成不必要的内存占用

综上所述，后续我们在使用复用机制的时候，例如日历，可以复用大cell然后嵌套子View去实现，并且，一定要一次性addSubView后再单独控制子view的显示。此种做法，对于性能的要求最小