在 iOS 7 下运行我的 iOS 6 应用程序时，为啥我的视图上没有正确显示阴影？

Posted 2023-03-12

【中文标题】在 iOS 7 下运行我的 iOS 6 应用程序时，为啥我的视图上没有正确显示阴影？

【英文标题】：Why are shadows not appearing correctly on my views when running my iOS 6 app under iOS 7?在 iOS 7 下运行我的 iOS 6 应用程序时，为什么我的视图上没有正确显示阴影？

【发布时间】：2013-10-22 15:18:52

【问题描述】：

我有一个尚未更新到 ios 7 的 iOS 6 应用程序。我的阴影出现了一些奇怪的颜色问题，这些问题只出现在 iOS 7 上。有时它们看起来正常，有时它们是彩色的。

正常（50% 的时间阴影在 iOS 7 上正常显示）：

彩色（50% 的时间它们以这种方式出现。它们应该像上面一样是黑色的。似乎在移入和移出视图时发生）：

有人有什么想法吗？这是我已经使用了两年多的代码。有一个更好的方法吗？这里是否有更新的 API 调用不正确？

ShadowedTableView.h

#import <UIKit/UIKit.h>
#import <QuartzCore/QuartzCore.h>

@interface ShadowedTableView : UITableView

    CAGradientLayer *originShadow;
    CAGradientLayer *topShadow;
    CAGradientLayer *bottomShadow;


@end

ShadowedTableView.m

#import "ShadowedTableView.h"

#define SHADOW_HEIGHT 20.0
#define SHADOW_INVERSE_HEIGHT 10.0
#define SHADOW_RATIO (SHADOW_INVERSE_HEIGHT / SHADOW_HEIGHT)

@implementation ShadowedTableView

//
// shadowAsInverse:
//
// Create a shadow layer
//
// Parameters:
//    inverse - if YES then shadow fades upwards, otherwise shadow fades downwards
//
// returns the constructed shadow layer
//
- (CAGradientLayer *)shadowAsInverse:(BOOL)inverse

    CAGradientLayer *newShadow = [[CAGradientLayer alloc] init];
    CGRect newShadowFrame =
        CGRectMake(0, 0, self.frame.size.width,
            inverse ? SHADOW_INVERSE_HEIGHT : SHADOW_HEIGHT);
    newShadow.frame = newShadowFrame;
    newShadow.colors =
        @[(__bridge id)(inverse ? 
                       ([self.backgroundColor colorWithAlphaComponent:0.0].CGColor) :
                       ([UIColor colorWithRed:0.0 green:0.0 blue:0.0 alpha:inverse ? (SHADOW_INVERSE_HEIGHT / SHADOW_HEIGHT) * 0.5 : 0.5].CGColor)),
         (__bridge id)(inverse ? 
                       ([UIColor colorWithRed:0.0 green:0.0 blue:0.0 alpha:inverse ? (SHADOW_INVERSE_HEIGHT / SHADOW_HEIGHT) * 0.5 : 0.5].CGColor) :
                       ([self.backgroundColor colorWithAlphaComponent:0.0].CGColor))];
    return newShadow;


//
// layoutSubviews
//
// Override to layout the shadows when cells are laid out.
//
- (void)layoutSubviews

    [super layoutSubviews];

    //
    // Construct the origin shadow if needed
    //
    if (!originShadow)
    
        originShadow = [self shadowAsInverse:NO];
        [self.layer insertSublayer:originShadow atIndex:0];
    
    else if (![(self.layer.sublayers)[0] isEqual:originShadow])
    
        [self.layer insertSublayer:originShadow atIndex:0];
    

    [CATransaction begin];
    [CATransaction setValue:(id)kCFBooleanTrue forKey:kCATransactionDisableActions];

    //
    // Stretch and place the origin shadow
    //
    CGRect originShadowFrame = originShadow.frame;
    originShadowFrame.size.width = self.frame.size.width;
    originShadowFrame.origin.y = self.contentOffset.y;
    originShadow.frame = originShadowFrame;

    [CATransaction commit];

    if (self.style == UITableViewStylePlain)
    
        NSArray *indexPathsForVisibleRows = [self indexPathsForVisibleRows];
        if ([indexPathsForVisibleRows count] == 0)
        
            [topShadow removeFromSuperlayer];
            topShadow = nil;
            [bottomShadow removeFromSuperlayer];
            bottomShadow = nil;
            return;
        

        NSIndexPath *firstRow = indexPathsForVisibleRows[0];
        if ([firstRow section] == 0 && [firstRow row] == 0)
        
            UIView *cell = [self cellForRowAtIndexPath:firstRow];
            if (!topShadow)
            
                topShadow = [self shadowAsInverse:YES];
                [cell.layer insertSublayer:topShadow atIndex:0];
            
            else if ([cell.layer.sublayers indexOfObjectIdenticalTo:topShadow] != 0)
            
                [cell.layer insertSublayer:topShadow atIndex:0];
            

            CGRect shadowFrame = topShadow.frame;
            shadowFrame.size.width = cell.frame.size.width;
            shadowFrame.origin.y = -SHADOW_INVERSE_HEIGHT;
            topShadow.frame = shadowFrame;
        
        else
        
            [topShadow removeFromSuperlayer];
            topShadow = nil;
        

        NSIndexPath *lastRow = [indexPathsForVisibleRows lastObject];
        if ([lastRow section] == [self numberOfSections] - 1 &&
            [lastRow row] == [self numberOfRowsInSection:[lastRow section]] - 1)
        
            UIView *cell =
            [self cellForRowAtIndexPath:lastRow];
            if (!bottomShadow)
            
                bottomShadow = [self shadowAsInverse:NO];
                [cell.layer insertSublayer:bottomShadow atIndex:0];
            
            else if ([cell.layer.sublayers indexOfObjectIdenticalTo:bottomShadow] != 0)
            
                [cell.layer insertSublayer:bottomShadow atIndex:0];
            

            CGRect shadowFrame = bottomShadow.frame;
            shadowFrame.size.width = cell.frame.size.width;
            shadowFrame.origin.y = cell.frame.size.height;
            bottomShadow.frame = shadowFrame;
        
        else
        
            [bottomShadow removeFromSuperlayer];
            bottomShadow = nil;
        
    


//
// dealloc
//
// Releases instance memory.
//


@end

【问题讨论】：

不记得细节，但他们确实更新了导航栏上阴影的显示方式。

【参考方案1】：

似乎 CAGradientLayer 需要 0,0,0,0 的 RGBA 来制作完全透明的颜色，这意味着它的混合模式在 iOS 7 中发生了变化。我已经为此提交了一份雷达 (#15336983)。

无论如何，解决方法是替换：

([self.backgroundColor colorWithAlphaComponent:0.0].CGColor) :

与：

([UIColor colorWithRed:0.0 green:0.0 blue:0.0 alpha:0.0].CGColor) :