collectionView 都是从第一位开始的,想要达到居中的效果就要自定义一个瀑布流.一个小 demo, 和大家分享一下.
在 viewcontroller 里面
#import "ViewController.h"
#import "CustomFlowLayout.h"
#define ScreenWidth [UIScreen mainScreen].bounds.size.width
#define ScreenHeight [UIScreen mainScreen].bounds.size.height
#define Scale [UIScreen mainScreen].bounds.size.width / 320
#define kMinimumLineSpacing 20
#define kMinimumInteritemSpacing 15
#define kItemWidth 45
#define kItemHeight kItemWidth
#define WIDTH self.view.frame.size.width
@interface ViewController ()
@property (nonatomic, strong) UICollectionView*myCollectionView;
@property (nonatomic, strong) CustomFlowLayout *flowLayout;
@property (nonatomic, strong) NSMutableArray *itemArray;
@end
@implementation ViewController
- (void)viewDidLoad{
[super viewDidLoad];
self.view.backgroundColor = [UIColor whiteColor];
_flowLayout = [[CustomFlowLayout alloc] init];
// 设置滚动方向
_flowLayout.scrollDirection = UICollectionViewScrollDirectionVertical;
// 设置item大小
_flowLayout.itemSize = CGSizeMake(kItemWidth * Scale, kItemHeight * Scale);
// 设置最小行间距
_flowLayout.minimumLineSpacing = kMinimumLineSpacing * Scale;
// 设置最小列间距
_flowLayout.minimumInteritemSpacing = kMinimumInteritemSpacing * Scale;
// 设置一个item边框,上下左右边距大小
_flowLayout.sectionInset = UIEdgeInsetsMake(kMinimumLineSpacing * Scale, 16.5 * Scale, 0, 16.5 * Scale);
for (int i = 0; i < 9; i++) {
NSNumber *number = [NSNumber numberWithInt:i];
[self.itemArray addObject:number];
}
NSInteger lineRow = 0;
NSInteger remainder = _itemArray.count % 5;
if (remainder == 0) {
lineRow = _itemArray.count / 5;
}else {
lineRow = _itemArray.count / 5 + 1;
}
_myCollectionView = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 0.4625 * WIDTH, ScreenWidth, ((kMinimumLineSpacing + kItemHeight) * Scale) * lineRow + kMinimumLineSpacing) collectionViewLayout:_flowLayout];
_myCollectionView.dataSource = self;
_myCollectionView.delegate = self;
_myCollectionView.backgroundColor = [UIColor cyanColor];
[_myCollectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"FightGroupsDetailCollectionCellReuse"];
[self.view addSubview:_myCollectionView];
}
- (NSMutableArray *)itemArray{
if (!_itemArray) {
_itemArray = [NSMutableArray array];
}
return _itemArray;
}
#pragma mark - collectionView的协议方法
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{
return _itemArray.count;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"FightGroupsDetailCollectionCellReuse" forIndexPath:indexPath]; cell.backgroundColor = [UIColor redColor];
return cell;
}
CustomFlowLayout- (NSArray*)layoutAttributesForElementsInRect:(CGRect)rect
{
NSArray* attributesToReturn = [super layoutAttributesForElementsInRect:rect];
for (UICollectionViewLayoutAttributes* attributes in attributesToReturn) {
if (nil == attributes.representedElementKind) {
NSIndexPath* indexPath = attributes.indexPath;
attributes.frame = [self layoutAttributesForItemAtIndexPath:indexPath].frame;
}
}
return attributesToReturn;
}
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
UICollectionViewLayoutAttributes *currentItemAttributes = [super layoutAttributesForItemAtIndexPath:indexPath];
NSInteger sectionCount = [self.collectionView numberOfSections];
NSInteger itemCount = 0;
for (int i = 0; i < sectionCount; i++) {
NSInteger rowCount = [self.collectionView numberOfItemsInSection:i];
itemCount = itemCount + rowCount;
}
// 余数
NSInteger yushu = itemCount % itemOneLineCount;
// 行数
NSInteger hangshu = itemCount / itemOneLineCount;
if (indexPath.item > hangshu * itemOneLineCount - 1) {
NSInteger index = indexPath.item - (hangshu * itemOneLineCount - 1);
switch (yushu) {
case 1: {
// 最后一行只有一个时候
// 由于作用域的问题 必须｛｝扩起来
CGPoint currentItemCenter = [currentItemAttributes center];
currentItemCenter.x = SCREENW / 2;
currentItemAttributes.center = currentItemCenter;
}
break;
case 2: {
// 最后一行只有两个时候
CGRect currentItemFrame = [currentItemAttributes frame];
if (index == 1) {
// 最后一行第一个
// (屏幕宽度 －（两个itemsize的宽度 ＋ 中间间隔）) / 2
currentItemFrame.origin.x = SCREENW / 2 - kMinimumInteritemSpacing * Scale / 2 - kItemWidth * Scale;
} else if (index == 2) {
// (屏幕宽度 － （两个itemsize的宽度 ＋ 中间间隔）) / 2 + 中间间隔 ＋ itemsize宽度
currentItemFrame.origin.x = SCREENW / 2 + kMinimumInteritemSpacing * Scale / 2;
}
currentItemAttributes.frame = currentItemFrame;
}
break;
case 3: {
CGRect currentItemFrame = [currentItemAttributes frame];
if (index == 1) {
currentItemFrame.origin.x = SCREENW / 2 - kMinimumInteritemSpacing * Scale - kItemWidth * Scale * 1.5;
} else if (index == 2) {
currentItemFrame.origin.x = SCREENW / 2 - kItemWidth * Scale / 2;
} else if (index == 3) {
currentItemFrame.origin.x = SCREENW / 2 + kItemWidth * Scale / 2 + kMinimumInteritemSpacing * Scale;
}
currentItemAttributes.frame = currentItemFrame;
}
break;
case 4: {
CGRect currentItemFrame = [currentItemAttributes frame];
if (index == 1) {
currentItemFrame.origin.x = SCREENW / 2 - kMinimumInteritemSpacing * Scale * 1.5 - kItemWidth * Scale * 2;
} else if (index == 2) {
currentItemFrame.origin.x = SCREENW / 2 - kMinimumInteritemSpacing / 2 - kItemWidth * Scale;
} else if (index == 3) {
currentItemFrame.origin.x = SCREENW / 2 + kMinimumInteritemSpacing * Scale / 2;
} else if (index == 4) {
currentItemFrame.origin.x = SCREENW / 2 + kItemWidth * Scale + kMinimumInteritemSpacing * Scale * 1.5;
}
currentItemAttributes.frame = currentItemFrame;
}
break;
default:
break;
}
}
return currentItemAttributes;
}
@end
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