Banner, 小众三方库WSCycle 源码分析

目标，侧边图，先缩小，再调整间距
比较麻烦的是， 自定义的 banner视图回收机制 和 坐标换算(因为里面有一个视图层级关系)

• 重写 _scrollViewDen.frame ， 覆盖原来的
• [_dataSource numberOfPagesInFlowView:self] * 3; 我觉得 多了，
  应该是 ，多于两张视图的情况下， +1 ，就好了

- (void)layoutSubviews{
    [super layoutSubviews];

    //重置pageCount
    if (_dataSource && [_dataSource respondsToSelector:@selector(numberOfPagesInFlowView:)]) {
        //原始页数
        self.orginPageCount = [_dataSource numberOfPagesInFlowView:self];
        //总页数
        _pageCount = self.orginPageCount == 1 ? 1: [_dataSource numberOfPagesInFlowView:self] * 3;
//我觉得 多了，   应该是 ，多于两张视图的情况下， +1 ，就好了
        if (self.pageControl && [self.pageControl respondsToSelector:@selector(setNumberOfPages:)]) {
            [self.pageControl setNumberOfPages:self.orginPageCount];
        }
    }
    //重置pageWidth
    if (_delegate && [_delegate respondsToSelector:@selector(sizeForPageInFlowView:)]) {
        _pageSize = [_delegate sizeForPageInFlowView:self];
        _sideCellWidth = _pageSize.width * kZoomInPageScale + 2*kInteritemSpacing ;
    }
    [_reusableCells removeAllObjects];
    _visibleRange = NSMakeRange(0, 0);
    //填充cells数组
    [_mutableCells removeAllObjects];
    for (NSInteger index=0; index<_pageCount; index++){
        [_mutableCells addObject:[NSNull null]];
    }
    
    _scrollViewDen.frame = CGRectMake(0, 0, _pageSize.width, _pageSize.height); // 这行代码 ，涉及坐标转换， 很 关键 Deng
    
    CGFloat contentWidthDen = _sideCellWidth * (_pageCount - 1) + _pageSize.width;
    
    _scrollViewDen.contentSize = CGSizeMake(contentWidthDen, _pageSize.height);
    CGPoint theCenter = CGPointMake(CGRectGetMidX(self.bounds), CGRectGetMidY(self.bounds));
    _scrollViewDen.center = theCenter;
    if (self.orginPageCount > 1) {
        //不仅仅 只有一张图 , 滚到第二组
        [_scrollViewDen setContentOffset: CGPointMake(_sideCellWidth, 0) animated:NO];
        self.pageIndex = self.orginPageCount;
    }
    [self toSetPagesAtContentOffset: _scrollViewDen.contentOffset];//根据当前scrollView的offset设置cell
    [self refreshVisibleCellAppearance];//更新各个可见Cell的显示外貌
    
}

想要先缩小侧边图，再调整间距， 感觉ScrollView 的 不足（先天不足），他是这么算的。

• CGRect originCellFrame = CGRectMake(_sideCellWidth * i, 0, _pageSize.width, _pageSize.height);//如果没有缩小效果的情况下的本该的Frame
  调整ScrollView上面的间距， 就是 修改addSubView的 view的originX,
  不应该用乘法，应该用加法， 至少乘法需要条件判断

• cellIndexBanner.frame = UIEdgeInsetsInsetRect(originCellFrame, UIEdgeInsetsMake(insetV, kInteritemSpacing, insetV, kInteritemSpacing));
  所以感觉ScrollView addSubView 的 centerPoint没变， 以此为中心，缩进缩小。
  以此库设置inter item spacing 困难， 需重新设计

- (void)refreshVisibleCellAppearance{
    CGFloat offset = _scrollViewDen.contentOffset.x;
    NSUInteger startIndex = self.visibleRange.location;
    NSUInteger endIndex = self.visibleRange.location + _visibleRange.length;
    for (NSUInteger i = startIndex; i < endIndex; i++) {
        WSIndexBanner *cellIndexBanner = [_mutableCells objectAtIndex:i];
        CGFloat origin = cellIndexBanner.frame.origin.x;
        CGFloat delta = fabs(origin - offset);
        CGRect originCellFrame = CGRectMake(_sideCellWidth * i, 0, _pageSize.width, _pageSize.height);//如果没有缩小效果的情况下的本该的Frame
        CGFloat insetV = _pageSize.width * (1 - kZoomInPageScale) / 2.0 ;
        if (delta < _pageSize.width) {
            cellIndexBanner.coverView.alpha = (delta / _pageSize.width) * (1 - _minimumPageAlpha);
            insetV = insetV * (delta / _sideCellWidth);
            cellIndexBanner.frame = UIEdgeInsetsInsetRect(originCellFrame, UIEdgeInsetsMake(insetV, kInteritemSpacing, insetV, kInteritemSpacing));
            cellIndexBanner.mainImageView.frame = cellIndexBanner.bounds;
        } else {
            cellIndexBanner.coverView.alpha = _minimumPageAlpha;
            cellIndexBanner.frame = UIEdgeInsetsInsetRect(originCellFrame, UIEdgeInsetsMake(insetV, kInteritemSpacing, insetV, kInteritemSpacing));
            cellIndexBanner.mainImageView.frame = cellIndexBanner.bounds;
        }
    }
}

或许 UICollectionFlowLayout ， 会合适一些