使用ARC绘制渐变时,CFArrayRef和NSArray出现问题

Question

我有一个ARC项目,我正在尝试绘制垂直线性渐变.下面的代码适用于模拟器,但EXC_BAD_ACCESS在设备上进行测试时会抛出内存/ 错误.该应用程序使用以下两行代码崩溃:

NSArray *colorArray = [NSArray arrayWithObjects:(__bridge id)topColor, (__bridge id)bottomColor, nil];
CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (__bridge CFArrayRef) colorArray, colorLocations); 

这两行代码取自以下代码(供参考):

- (void)drawRect:(CGRect)rect
{
    CGContextRef context = UIGraphicsGetCurrentContext();

    [self createGradientForContext:context andView:self.captionView];
    [self createGradientForContext:context andView:self.linksView];
    [self createGradientForContext:context andView:self.commentView]; 

}

- (void)createGradientForContext:(CGContextRef)context andView:(UIView *)view
{

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    CGFloat colorLocations[] = { 0.0f, 1.0f };

    CGColorRef topColor = [[UIColor colorWithRed:51.0f/255.0f green:51.0f/255.0f blue:51.0f/255.0f alpha:1.0f] CGColor];
    CGColorRef bottomColor = [[UIColor colorWithRed:48.0f/255.0f green:48.0f/255.0f blue:48.0f/255.0f alpha:1.0f] CGColor];
    NSArray *colorArray = [NSArray arrayWithObjects:(__bridge id)topColor, (__bridge id)bottomColor, nil];
    CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (__bridge_retained CFArrayRef) colorArray, colorLocations);    

    CGRect frame = view.frame;
    CGPoint startPoint = CGPointMake(CGRectGetMidX(frame), CGRectGetMinY(frame));
    CGPoint endPoint = CGPointMake(CGRectGetMidX(frame), CGRectGetMaxY(frame));

    CGContextSaveGState(context);
    CGContextAddRect(context, frame);
    CGContextClip(context);
    CGContextDrawLinearGradient(context, gradient, startPoint, endPoint, 0);
    CGContextRestoreGState(context);

    CGGradientRelease(gradient);
    CGColorSpaceRelease(colorSpace);

}

提前感谢任何和所有指导.

Answer 1

现在解释你崩溃的原因......

问题是这两行:

CGColorRef topColor = [[UIColor colorWithRed:51.0f/255.0f green:51.0f/255.0f blue:51.0f/255.0f alpha:1.0f] CGColor];
CGColorRef bottomColor = [[UIColor colorWithRed:48.0f/255.0f green:48.0f/255.0f blue:48.0f/255.0f alpha:1.0f] CGColor];

这是一个非常普遍的问题; 关于Stack Overflow的问题有很多被这个问题所困扰的用户.

问题是因为那些UIColor对象永远不会在这些行之后被引用,ARC会立即释放它们 - 因为这些UIColor对象是CGColor对象的唯一所有者,所以UIColors会立即释放CGColors,留下两个死CGColor对象.然后你尝试放入一个数组.

正如您所发现的,从NSArray切换到纯CFArray无法解决这个问题.从UIColor切换到纯CGColor是一种解决方案; 另一种是将自己的所有权放在CGColors上:

CGColorRef topColor = CGColorRetain([[UIColor colorWithRed:51.0f/255.0f green:51.0f/255.0f blue:51.0f/255.0f alpha:1.0f] CGColor]);
CGColorRef bottomColor = CGColorRetain([[UIColor colorWithRed:48.0f/255.0f green:48.0f/255.0f blue:48.0f/255.0f alpha:1.0f] CGColor]);

?

CGColorRelease(topColor);
CGColorRelease(bottomColor);

Answer 2

尝试使用a CFArrayRef并避免桥接,看看它是否有所作为.

CGFloat topColorComps[] = {51.0f/255.0f, 51.0f/255.0f, 51.0f/255.0f, 1.0f};
CGFloat bottomColorComps[] = {48.0f/255.0f, 48.0f/255.0f, 48.0f/255.0f, 1.0f};            

CGColorSpaceRef rgb = CGColorSpaceCreateDeviceRGB();
CGColorRef topColor = CGColorCreate(rgb, topColorComps);
CGColorRef bottomColor = CGColorCreate(rgb, bottomColorComps);
CGColorSpaceRelease(rgb);

CFMutableArrayRef colorArray = CFArrayCreateMutable(NULL, 2, &kCFTypeArrayCallbacks);
CFArrayAppendValue(colorArray, topColor);
CFArrayAppendValue(colorArray, bottomColor);

CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, colorArray, colorLocations);

CFRelease(colorArray);
CFRelease(topColor);
CFRelease(bottomColor);