最近在开发软件的时候被要求,要让UICollectionView上面的cell之间的距离固定,但是cell的宽度不一定,所以一行有几个cell其实不固定,跟cell中的label的text有关,剩下的空白格平均分配的. 效果如下：

首先控制cell间的间距固定，左边对齐(这部分，我主要参照文章UICollectionView中Cell左对齐 居中 右对齐 等间距)

EqualSpaceFlowLayoutEvolve继承UICollectionViewFlowLayout。 .m文件的代码如下：

-(instancetype)init{     
        if(self = [super init]){
            self.scrollDirection = UICollectionViewScrollDirectionVertical;  
            self.minimumLineSpacing =5;
            self.minimumInteritemSpacing =5;
            self.sectionInset = UIEdgeInsetsMake(0,0,0,0);
            _betweenOfCell = 5.0;
            _cellType = AlignWithLeft;    
      }     
    return self;
} 

-(void)setBetweenOfCell:(CGFloat)betweenOfCell{
     _betweenOfCell = betweenOfCell;     
     self.minimumInteritemSpacing = betweenOfCell; 
} 

-(instancetype)initWthType:(AlignType)cellType{    
       if(self = [super init]){
            self.scrollDirection = UICollectionViewScrollDirectionVertical;         
            self.minimumLineSpacing =5;
            self.minimumInteritemSpacing =5;
            self.sectionInset = UIEdgeInsetsMake(0,0,0,0);
            _betweenOfCell =5.0;        
           _cellType = cellType;
     } 
    return self;
}  

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {    
      NSArray *layoutAttributes_t = [super layoutAttributesForElementsInRect:rect];
      NSArray *layoutAttributes = [[NSArray alloc] initWithArray:layoutAttributes_t copyItems:YES]; 
      //用来临时存放一行的Cell数组
      NSMutableArray *layoutAttributesTemp = [[NSMutableArray alloc] init]; 

      for(NSUInteger index =0; index < layoutAttributes.count ; index++) {

           UICollectionViewLayoutAttributes *currentAttr = layoutAttributes[index];// 当前cell的位置信息   
           UICollectionViewLayoutAttributes *previousAttr = index ==0? nil : layoutAttributes[index-1];// 上一个cell 的位置信    
           UICollectionViewLayoutAttributes *nextAttr = index +1== layoutAttributes.count ?    nil : layoutAttributes[index+1];//下一个cell 位置信息   
 
           //加入临时数组   
           [layoutAttributesTemp addObject:currentAttr];     
           _sumWidth += currentAttr.frame.size.width;    
           CGFloat previousY = previousAttr == nil ? 0: CGRectGetMaxY(previousAttr.frame);
           CGFloat currentY = CGRectGetMaxY(currentAttr.frame);    
           CGFloat nextY = nextAttr == nil ?0: CGRectGetMaxY(nextAttr.frame);

           //如果当前cell是单独一行    
           if(currentY != previousY && currentY != nextY){
                 if([currentAttr.representedElementKind isEqualToString:UICollectionElementKindSectionHeader]) {
                       [layoutAttributesTemp removeAllObjects];            
                       _sumWidth =0.0;
                 }else if([currentAttr.representedElementKind isEqualToString:UICollectionElementKindSectionFooter]){
                       [layoutAttributesTemp removeAllObjects];             
                       _sumWidth =0.0;
                 }else{
                       [self setCellFrameWith:layoutAttributesTemp];         
                 }        
            }     
//如果下一个cell在本行，这开始调整Frame位置        
           else if( currentY != nextY) {
                 [self setCellFrameWith:layoutAttributesTemp];     
            }     
      }     
    return layoutAttributes;
} 

-(void)setCellFrameWith:(NSMutableArray*)layoutAttributes{
    CGFloat nowWidth =0.0;
    switch(_cellType) {
         case AlignWithLeft: {
               nowWidth = self.sectionInset.left;         
               for(UICollectionViewLayoutAttributes * attributesinlayoutAttributes) {
                    CGRect nowFrame = attributes.frame;            
                    nowFrame.origin.x = nowWidth;             
                    attributes.frame = nowFrame;            
                    nowWidth += nowFrame.size.width + self.betweenOfCell;         
                }        
                _sumWidth =0.0;
                [layoutAttributes removeAllObjects];   
        } 
              break;
         case AlignWithCenter: {
               nowWidth = (self.collectionView.frame.size.width - _sumWidth - ((layoutAttributes.count -1) * _betweenOfCell)) /2;
               for(UICollectionViewLayoutAttributes * attributesinlayoutAttributes) {
                     CGRect nowFrame = attributes.frame;             
                     nowFrame.origin.x = nowWidth;             
                     attributes.frame = nowFrame;            
                     nowWidth += nowFrame.size.width + self.betweenOfCell;        
                }        
                _sumWidth =0.0;
                [layoutAttributes removeAllObjects];        
        } 
               break;
         case AlignWithRight: {
               nowWidth = self.collectionView.frame.size.width - self.sectionInset.right;         
               for(NSInteger index = layoutAttributes.count -1; index >=0; index-- ) {
                    UICollectionViewLayoutAttributes * attributes = layoutAttributes[index];            
                    CGRect nowFrame = attributes.frame;             
                    nowFrame.origin.x = nowWidth - nowFrame.size.width;             
                    attributes.frame = nowFrame;             
                    nowWidth = nowWidth - nowFrame.size.width - _betweenOfCell;             
                    if(index ==0) {
                         CGRect nowFrame = attributes.frame;                
                         nowFrame.origin.x = nowWidth;                
                         attributes.frame = nowFrame;             
                     }        
                 }        
                 _sumWidth =0.0;
                 [layoutAttributes removeAllObjects];   
          } 
                break;
     } 
}

然后在创建collectionView的地方写下如下代码：

EqualSpaceFlowLayoutEvolve *flowLayout = [[EqualSpaceFlowLayoutEvolve alloc]    initWthType:AlignWithLeft]; 
flowLayout.betweenOfCell =15;
flowLayout.scrollDirection = UICollectionViewScrollDirectionVertical; 
flowLayout.sectionInset = UIEdgeInsetsMake(0,0,0,0);
_collectionView = [[UICollectionView alloc] initWithFrame:CGRectMake(0,0,100,100) collectionViewLayout:flowLayout];

就这样就可以控制cell的间距固定，左边对齐了

cell右边对齐
首先一个数组存cell上label的text，然后调用一下方法：

- (void)calculateItemWidthsWith:(NSArray *)array{
       _itemWidths = [NSMutableArray array];    
      CGFloat maxWidth = self.view.frame.size.width -40;
      CGFloat sumWidth =0;
      int count =0;
      for(inti =0; i < array.count; i++) {
          CGFloat itemWidth = [array[i] boundingRectWithSize:CGSizeMake(maxWidth,33) options:NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingUsesFontLeading | NSStringDrawingTruncatesLastVisibleLine attributes:@{NSFontAttributeName: [UIFont systemFontOfSize:15]} context:nil].size.width +45;
          itemWidth = itemWidth > maxWidth ? maxWidth : itemWidth;     
          sumWidth += itemWidth;     
          count +=1;
          if(sumWidth > maxWidth && i !=0) {
              // XXX: 在iPhone5下，得减去一点点数值(0.00001)，cell排序才不会乱           
              CGFloat subWidth = maxWidth - (sumWidth - itemWidth) -0.00001;
              CGFloat space = subWidth/(count -1);
              for(inth =1; h < count; h++) {
                   self.itemWidths[i-h] = [NSString stringWithFormat:@"%f", [_itemWidths[i-h] floatValue] + space];
              }        
              sumWidth = itemWidth;        
              count =1;
          }     
          [_itemWidths addObject:[NSString stringWithFormat:@"%f", itemWidth]];
      } 
}

最后调用一下方法即可

#pragma mark -  
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {     
    return CGSizeMake([self.itemWidths[indexPath.row] floatValue] -15,33);
}