UICollectionView自定义布局

例子：一个正方形里面排列不同大小的cell

1.继承UICollectionViewLayout
2.重写-(NSArray *)layoutAttributesForElementsInRect:(CGRect)rect

//设置所有cell的布局属性
-(NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSArray *arr = [super layoutAttributesForElementsInRect:rect];
    if ([arr count] > 0) {
        return arr;
    }
    
    NSMutableArray *attributes = [NSMutableArray array];
    for (NSInteger i = 0 ; i < [self.collectionView numberOfItemsInSection:0]; i++) {
        NSIndexPath *indexPath = [NSIndexPath indexPathForItem:i inSection:0];
        [attributes addObject:[self layoutAttributesForItemAtIndexPath:indexPath]];
    }
  
    return attributes;
}

3.重写

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewLayoutAttributes *attributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
    
    CGFloat width = self.collectionView.width;
    
    NSInteger count = [self.collectionView numberOfItemsInSection:0];
    if (count == 1) {
        attributes.size = CGSizeMake(width, width);
        attributes.center = CGPointMake(width/2, width/2);
    }else if (count == 2){
        CGFloat x = 0;
        CGFloat height = (self.collectionView.width-self.margin)/2;
        CGFloat y = indexPath.row * (height+self.margin);
        attributes.frame = CGRectMake(x, y, width, height);
    }
    else if (count == 3) {
        width = (self.collectionView.width-self.margin)/2;
        CGFloat height = (self.collectionView.width-self.margin)/2;
        CGFloat y = 0;
        CGFloat x = (indexPath.row-1) * (width + self.margin);
        if (indexPath.row == 0) {
            x = 0;
            y = 0;
            width = self.collectionView.width;
        }else {
            y = height + self.margin;
        }
        attributes.frame = CGRectMake(x, y, width, height);
    }
    else if (count == 4) {
        width = (self.collectionView.width-self.margin)/2;
        
        CGFloat y = 0;
        CGFloat x = 0;
        CGFloat height = width;
        x = indexPath.row%2 * (width + self.margin);
        if (indexPath.row < 2) {
            
        }else {
            y = height + self.margin;
        }
        attributes.frame = CGRectMake(x, y, width, height);
    }else if (count == 5) {
        CGFloat height = 0;
        CGFloat x = 0;
        CGFloat y = 0;
        if (indexPath.row == 0) {
            width = (self.collectionView.width-self.margin)/3*2;
            height = self.collectionView.width;
        }else {
            width = (self.collectionView.width-self.margin)/3;
            height = (self.collectionView.width - self.margin *3)/4;
            x = (self.collectionView.width-self.margin)/3*2 +self.margin;
            y = (indexPath.row -1) * (height + self.margin);
        }
        attributes.frame = CGRectMake(x, y, width, height);
        
    }else if (count == 6){
        width = (self.collectionView.width-self.margin)/2;
        CGFloat height = (self.collectionView.width-self.margin*2)/3;
        CGFloat y = 0;
        CGFloat x = 0;
        x = indexPath.row%2 * (width + self.margin);
        y = (indexPath.row/2)*(height +self.margin);
        attributes.frame = CGRectMake(x, y, width, height);
    }
 
    
    return attributes;
}

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