iOS开发之窥探UICollectionViewController(三) --使用UICollectionView自定义瀑布流

            1
            //
             The collection view calls -prepareLayout once at its first layout as the first message to the layout instance.

            2
            //
             The collection view calls -prepareLayout again after layout is invalidated and before requerying the layout information.

            3
            //
             Subclasses should always call super if they override.
            4 - (void)prepareLayout;

            1
            //
             Subclasses must override this method and use it to return the width and height of the collection view’s content. These values represent the width and height of all the content, not just the content that is currently visible. The collection view uses this information to configure its own content size to facilitate scrolling.
            2 - (CGSize)collectionViewContentSize; 

            1
            //
             UICollectionView calls these four methods to determine the layout information.

            2
            //
             Implement -layoutAttributesForElementsInRect: to return layout attributes for for supplementary or decoration views, or to perform layout in an as-needed-on-screen fashion.

            3
            //
             Additionally, all layout subclasses should implement -layoutAttributesForItemAtIndexPath: to return layout attributes instances on demand for specific index paths.

            4
            //
             If the layout supports any supplementary or decoration view types, it should also implement the respective atIndexPath: methods for those types.
            5 - (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect; // return an array layout attributes instances for all the views in the given rect6 - (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath;
7 - (UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryViewOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath;
8 - (UICollectionViewLayoutAttributes *)layoutAttributesForDecorationViewOfKind:(NSString*)elementKind atIndexPath:(NSIndexPath *)indexPath;

            1
            @property (nonatomic) CGRect frame;

            2
            @property (nonatomic) CGPoint center;

            3
            @property (nonatomic) CGSize size;

            4
            @property (nonatomic) CATransform3D transform3D;

            5
            @property (nonatomic) CGRect bounds NS_AVAILABLE_IOS(7_0);

            6
            @property (nonatomic) CGAffineTransform transform NS_AVAILABLE_IOS(7_0);

            7
            @property (nonatomic) CGFloat alpha;

            8 @property (nonatomic) NSInteger zIndex; // default is 09 @property (nonatomic, getter=isHidden) BOOL hidden; // As an optimization, UICollectionView might not create a view for items whose hidden attribute is YES

             1
            #pragma mark -- <UICollectionViewLayout>虚基类中重写的方法
 2 3/**
 4 * 该方法是预加载layout, 只会被执行一次
 5*/ 6 - (void)prepareLayout{
 7    [super prepareLayout];
 8 9    [self initData];
1011    [self initCellWidth];
1213    [self initCellHeight];
1415 }

            1
            /*
            *

            2
             * 该方法返回CollectionView的ContentSize的大小

            3
            */
            4 - (CGSize)collectionViewContentSize{
56     CGFloat height = [self maxCellYArrayWithArray:_cellYArray];
78return CGSizeMake(SCREEN_WIDTH,  height);
9 }

             1
            /*
            *

             2
             * 该方法为每个Cell绑定一个Layout属性~

             3
            */
             4 - (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
 5{
 6 7    [self initCellYArray];
 8 9     NSMutableArray *array = [NSMutableArray array];
1011//add cells12for (int i=0; i < _numberOfCellsInSections; i++)
13    {
14         NSIndexPath *indexPath = [NSIndexPath indexPathForItem:i inSection:0];
1516         UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForItemAtIndexPath:indexPath];
1718        [array addObject:attributes];
19    }
2021return array;
2223 }

            /*
            *
 * 该方法为每个Cell绑定一个Layout属性~
 
            */
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath{
    
    UICollectionViewLayoutAttributes *attributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
    
    CGRect frame = CGRectZero;
    
    CGFloat cellHeight = [_cellHeightArray[indexPath.row] floatValue];
    
    NSInteger minYIndex = [self minCellYArrayWithArray:_cellYArray];
    
    CGFloat tempX = [_cellXArray[minYIndex] floatValue];
    
    CGFloat tempY = [_cellYArray[minYIndex] floatValue];
    
    frame = CGRectMake(tempX, tempY, _cellWidth, cellHeight);
    
    //更新相应的Y坐标
    _cellYArray[minYIndex] = @(tempY + cellHeight + _padding);
    
    //计算每个Cell的位置
    attributes.frame = frame;
    
    return attributes;
}

            /*
            *
 * 初始化相关数据
 
            */
- (void) initData{
    _numberOfSections = [self.collectionView numberOfSections];
    _numberOfCellsInSections = [self.collectionView numberOfItemsInSection:0];
    
    //通过回调获取列数
    _columnCount = 5;
    _padding = 5;
    _cellMinHeight = 50;
    _cellMaxHeight = 150;
}

             1
            /*
            *

             2
             * 根据Cell的列数求出Cell的宽度

             3
            */
             4 - (void) initCellWidth{
 5//计算每个Cell的宽度 6     _cellWidth = (SCREEN_WIDTH - (_columnCount -1) * _padding) / _columnCount;
 7 8//为每个Cell计算X坐标 9     _cellXArray = [[NSMutableArray alloc] initWithCapacity:_columnCount];
10for (int i = 0; i < _columnCount; i ++) {
1112         CGFloat tempX = i * (_cellWidth + _padding);
1314        [_cellXArray addObject:@(tempX)];
15    }
1617 }

             1
            /*
            *

             2
             * 随机生成Cell的高度

             3
            */
             4 - (void) initCellHeight{
 5//随机生成Cell的高度 6     _cellHeightArray = [[NSMutableArray alloc] initWithCapacity:_numberOfCellsInSections];
 7for (int i = 0; i < _numberOfCellsInSections; i ++) {
 8 9         CGFloat cellHeight = arc4random() % (_cellMaxHeight - _cellMinHeight) + _cellMinHeight;
1011        [_cellHeightArray addObject:@(cellHeight)];
12    }
1314 }

            /*
            *
 * 初始化每列Cell的Y轴坐标
 
            */
- (void) initCellYArray{
    _cellYArray = [[NSMutableArray alloc] initWithCapacity:_columnCount];
    
    for (int i = 0; i < _columnCount; i ++) {
        [_cellYArray addObject:@(0)];
    }
}

             1
            /*
            *

             2
             * 求CellY数组中的最大值并返回

             3
            */
             4 - (CGFloat) maxCellYArrayWithArray: (NSMutableArray *) array{
 5if (array.count == 0) {
 6return0.0f;
 7    }
 8 9     CGFloat max = [array[0] floatValue];
10for (NSNumber *number in array) {
1112         CGFloat temp = [number floatValue];
1314if (max < temp) {
15             max = temp;
16        }
17    }
1819return max;
20 }

             1
            /*
            *

             2
             * 求CellY数组中的最小值的索引

             3
            */
             4 - (CGFloat) minCellYArrayWithArray: (NSMutableArray *) array{
 5 6if (array.count == 0) {
 7return0.0f;
 8    }
 910     NSInteger minIndex = 0;
11     CGFloat min = [array[0] floatValue];
1213for (int i = 0; i < array.count; i ++) {
14         CGFloat temp = [array[i] floatValue];
1516if (min > temp) {
17             min = temp;
18             minIndex = i;
19        }
20    }
2122return minIndex;
23 }