objective-c – 对CGImageCreate的正确调用是什么样的,如果它的

static const size_t kComponentsPerPixel = 4;
static const size_t kBitsPerComponent = sizeof(unsigned char) * 8;

NSInteger layerHeight = 160;
NSInteger layerWidth = 160;
CGContextSaveGState(context); 

CGColorSpaceRef rgb = CGColorSpaceCreateDeviceRGB();

size_t bufferLength = layerWidth * layerHeight * kComponentsPerPixel;

unsigned char *buffer = malloc(bufferLength);

// The real function does something more interesting with the buffer,but I cut it 
// to reduce the complexity while I figure out the crash.
for (NSInteger i = 0; i < bufferLength; ++i)
{
    buffer[i] = 255;
}
//memset(buffer,255,bufferLength);

CGDataProviderRef provider = 
CGDataProviderCreateWithData(NULL,&buffer,bufferLength,NULL);//freeBitmapBuffer);

CGImageRef imageRef = 
CGImageCreate(layerWidth,layerHeight,kBitsPerComponent,kBitsPerComponent * kComponentsPerPixel,kComponentsPerPixel * layerWidth,rgb,kCGBitmapByteOrderDefault | kCGImageAlphaLast,provider,NULL,false,kCGRenderingIntentDefault);

CGContextDrawImage(context,CGRectMake(0,160,160),imageRef);

CGImageRelease(imageRef);
CGDataProviderRelease(provider);
CGColorSpaceRelease(rgb);     

CGContextRestoreGState(context);

之后,当drawLayer：inContext：调用CGContextFillRect来显示由这个函数创建的模式时,我得到EXC_BAD_ACCESS.堆栈的顶部是CGSConvertAlphaByte.那时我看着缓冲区的内存,似乎很好 – 设置为调用模式函数时设置的内容.

我认为也许我搞砸了CGImageCreate的一些参数,很可能是标志.或者缓冲区没有以正确的顺序填充,但是如果我用相同的值填充每个字节,我不知道我怎么会出错.

任何类似的代码的想法或例子是非崩溃的？