【iOS】仿喜马拉雅首页背景颜色渐变效果

前言

以前公司要求实现喜马拉雅的首页背景颜色渐变效果，因而花了一段时间实现了出来，在这里记录下，实现该效果主要用到了下面两个库： JXCategoryView一个功能强大的分类控件 GKCycleScrollView我本身写的一个轮播图控件git

效果图

先来看下效果图： github

说明

经过研究喜马拉雅首页你会发现，要实现该功能有三个地方须要注意一、轮播图的滑动（左右滑动背景颜色根据图片渐变）二、分类切换页面（两个页面的当前背景色渐变）三、页面上下滑动（滑动到临界位置后背景色再也不根据轮播图变化）下面来讲明下实现过程 JXCategoryView里面有个方法，传入两个颜色及渐变百分比，返回对应的渐变颜色，这里直接用这个方法实现渐变bash

一、轮播图滑动

轮播图用的GKCycleScrollView,须要监听UIScrollView的滑动，根据滑动的距离和方向，计算出当前图片和下一张图片以及渐变百分比，下面看下具体代码：微信

// 滑动渐变背景色
- (void)cycleScrollView:(GKCycleScrollView *)cycleScrollView didScroll:(UIScrollView *)scrollView {
    if (self.isCriticalPoint) return;
    
    CGFloat offsetX = scrollView.contentOffset.x;
    CGFloat maxW = self.bannerLists.count * scrollView.bounds.size.width;
    
    CGFloat changeOffsetX = offsetX - maxW;
    
    BOOL isFirstRight = NO;
    
    if (changeOffsetX < 0) {
        changeOffsetX = -changeOffsetX;
        isFirstRight = YES;
    }
    
    CGFloat ratio = (changeOffsetX / scrollView.bounds.size.width);
    
    // 超过了边界，不须要处理
    if (ratio > self.bannerLists.count || ratio < 0) return;
    
    ratio = MAX(0, MIN(self.bannerLists.count, ratio));
    
    NSInteger baseIndex = floorf(ratio);
    
    // 最后一个
    if (baseIndex + 1 > self.bannerLists.count) {
        baseIndex = 0;
    }
    
    CGFloat remainderRatio = ratio - baseIndex;
    if (remainderRatio <= 0 || remainderRatio >= 1) return;
    
    GKHomeBannerModel *leftModel  = self.bannerLists[baseIndex];
    
    NSInteger nextIndex = 0;
    if (isFirstRight) {
        nextIndex = self.bannerLists.count - 1;
    }else if (baseIndex == self.bannerLists.count - 1) {
        nextIndex = 0;
    }else {
        nextIndex = baseIndex + 1;
    }
    
    GKHomeBannerModel *rightModel = self.bannerLists[nextIndex];
    
    UIColor *leftColor  = leftModel.headerBgColor ? leftModel.headerBgColor : GKHomeBGColor;
    UIColor *rightColor = rightModel.headerBgColor ? rightModel.headerBgColor : GKHomeBGColor;
    
    UIColor *color = [JXCategoryFactory interpolationColorFrom:leftColor to:rightColor percent:remainderRatio];
    
    self.bgColor = color;
    
    if (self.isSelected && [self.delegate respondsToSelector:@selector(listVC:didChangeColor:)]) {
        [self.delegate listVC:self didChangeColor:color];
    }
}
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二、分类切换页面

监听JXCategoryView的delegate方法，根据滑动距离找出当前页面和下一个页面及滑动百分比，渐变背景颜色markdown

- (void)categoryView:(JXCategoryBaseView *)categoryView scrollingFromLeftIndex:(NSInteger)leftIndex toRightIndex:(NSInteger)rightIndex ratio:(CGFloat)ratio {
    
    GKListViewController *leftVC  = (GKListViewController *)self.containerView.validListDict[@(leftIndex)];
    GKListViewController *rightVC = (GKListViewController *)self.containerView.validListDict[@(rightIndex)];
    
    UIColor *leftColor  = leftVC.isCriticalPoint ? [UIColor whiteColor] : leftVC.bgColor;
    UIColor *rightColor = rightVC.isCriticalPoint ? [UIColor whiteColor] : rightVC.bgColor;
    
    UIColor *color = [JXCategoryFactory interpolationColorFrom:leftColor to:rightColor percent:ratio];
    
    self.headerBgView.backgroundColor = color;
    
    // 两边状态同样，不用改变
    if (leftVC.isCriticalPoint == rightVC.isCriticalPoint) return;
    
    if (leftVC.isCriticalPoint) {
        if (ratio > 0.5) {
            [self changeToWhiteStateAtVC:nil];
        }else {
            [self changeToBlackStateAtVC:nil];
        }
    }else if (rightVC.isCriticalPoint) {
        if (ratio > 0.5) {
            [self changeToBlackStateAtVC:nil];
        }else {
            [self changeToWhiteStateAtVC:nil];
        }
    }
}
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三、页面上下滑动

监听列表的上下滑动，根据滑动距离判断是否到底临界点，改变分类的背景色oop

- (void)listVC:(GKListViewController *)vc didScroll:(UIScrollView *)scrollView {
    if (self.style == GKHomeThemeStyleNone) return;
    
    CGFloat offsetY = scrollView.contentOffset.y;
    if (offsetY <= 0) return;
    
    if (offsetY > ADAPTATIONRATIO * 360.0f) {
        [self changeToBlackStateAtVC:vc];
    }else {
        [self changeToWhiteStateAtVC:vc];
    }
}
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四、动态刷新标题颜色和指示器颜色

关于动态改变标题颜色、指示器颜色JXCategoryView并无提供相关方法，因而经过查看相关代码，找到了下面的解决办法，经过对JXCategoryTitleView添加分类实现ui

- (void)refreshCellState {
    [self.dataSource enumerateObjectsUsingBlock:^(JXCategoryBaseCellModel * _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
        [self reloadCellAtIndex:idx];
    }];
    
    CGRect selectedCellFrame = CGRectZero;
    JXCategoryIndicatorCellModel *selectedCellModel = nil;
    for (int i = 0; i < self.dataSource.count; i++) {
        JXCategoryIndicatorCellModel *cellModel = (JXCategoryIndicatorCellModel *)self.dataSource[i];
        cellModel.sepratorLineShowEnabled = self.isSeparatorLineShowEnabled;
        cellModel.separatorLineColor = self.separatorLineColor;
        cellModel.separatorLineSize = self.separatorLineSize;
        cellModel.backgroundViewMaskFrame = CGRectZero;
        cellModel.cellBackgroundColorGradientEnabled = self.isCellBackgroundColorGradientEnabled;
        cellModel.cellBackgroundSelectedColor = self.cellBackgroundSelectedColor;
        cellModel.cellBackgroundUnselectedColor = self.cellBackgroundUnselectedColor;
        if (i == self.dataSource.count - 1) {
            cellModel.sepratorLineShowEnabled = NO;
        }
        if (i == self.selectedIndex) {
            selectedCellModel = cellModel;
            selectedCellFrame = [self getTargetCellFrame:i];
        }
    }
    
    for (UIView<JXCategoryIndicatorProtocol> *indicator in self.indicators) {
        if (self.dataSource.count <= 0) {
            indicator.hidden = YES;
        }else {
            indicator.hidden = NO;
            JXCategoryIndicatorParamsModel *indicatorParamsModel = [[JXCategoryIndicatorParamsModel alloc] init];
            indicatorParamsModel.selectedIndex = self.selectedIndex;
            indicatorParamsModel.selectedCellFrame = selectedCellFrame;
            [indicator jx_refreshState:indicatorParamsModel];
        }
    }
}
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到这里主要的功能点就已经实现了，固然还有不少细节，若是想了解，能够到github 上查阅相关代码。spa

最后

仿喜马拉雅首页背景颜色渐变效果不少APP都在用，若是你须要的话能够在GKXimalaya中查看若是您以为还不错，还请点个star，您的支持是我最大的动力。code

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