【iOS】仿喜馬拉雅首頁背景顏色漸變效果

前言

以前公司要求實現喜馬拉雅的首頁背景顏色漸變效果，因而花了一段時間實現了出來，在這裏記錄下，實現該效果主要用到了下面兩個庫： JXCategoryView一個功能強大的分類控件 GKCycleScrollView我本身寫的一個輪播圖控件git

效果圖

先來看下效果圖： github

說明

經過研究喜馬拉雅首頁你會發現，要實現該功能有三個地方須要注意一、輪播圖的滑動（左右滑動背景顏色根據圖片漸變）二、分類切換頁面（兩個頁面的當前背景色漸變）三、頁面上下滑動（滑動到臨界位置後背景色再也不根據輪播圖變化）下面來講明下實現過程 JXCategoryView裏面有個方法，傳入兩個顏色及漸變百分比，返回對應的漸變顏色，這裏直接用這個方法實現漸變bash

一、輪播圖滑動

輪播圖用的GKCycleScrollView,須要監聽UIScrollView的滑動，根據滑動的距離和方向，計算出當前圖片和下一張圖片以及漸變百分比，下面看下具體代碼：微信

// 滑動漸變背景色
- (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);
    
    // 超過了邊界，不須要處理
    if (ratio > self.bannerLists.count || ratio < 0) return;
    
    ratio = MAX(0, MIN(self.bannerLists.count, ratio));
    
    NSInteger baseIndex = floorf(ratio);
    
    // 最後一個
    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、分類切換頁面

監聽JXCategoryView的delegate方法，根據滑動距離找出當前頁面和下一個頁面及滑動百分比，漸變背景顏色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;
    
    // 兩邊狀態同樣，不用改變
    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、頁面上下滑動

監聽列表的上下滑動，根據滑動距離判斷是否到底臨界點，改變分類的背景色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、動態刷新標題顏色和指示器顏色

關於動態改變標題顏色、指示器顏色JXCategoryView並無提供相關方法，因而經過查看相關代碼，找到了下面的解決辦法，經過對JXCategoryTitleView添加分類實現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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到這裏主要的功能點就已經實現了，固然還有不少細節，若是想了解，能夠到github 上查閱相關代碼。spa

最後

仿喜馬拉雅首頁背景顏色漸變效果不少APP都在用，若是你須要的話能夠在GKXimalaya中查看若是您以爲還不錯，還請點個star，您的支持是我最大的動力。code

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