[英]unsigned long , unsigned char in Objective C to Swift
[英]unsigned char allocation comes nils in offset value objective c
我正在从触摸点获取像素颜色值。 我已成功完成此操作,但有时应用程序给出了错误信息(EXC_BAD_ACCESS(CODE = 1,address = 0x41f6864)。此处的内存分配问题是供您参考的源代码。
- (UIColor *) getPixelColorAtLocation:(CGPoint)point {
UIColor* color = nil;
@try{
{
CGImageRef inImage = drawImage.image.CGImage;
// Create off screen bitmap context to draw the image into. Format ARGB is 4 bytes for each pixel: Alpa, Red, Green, Blue
CGContextRef cgctx = [self createARGBBitmapContextFromImage:inImage];
if (cgctx == NULL)
{
return nil; /* error */
}
size_t w = CGImageGetWidth(inImage);
size_t h = CGImageGetHeight(inImage);
CGRect rect = {{0,0},{w,h}};
// Draw the image to the bitmap context. Once we draw, the memory
// allocated for the context for rendering will then contain the
// raw image data in the specified color space.
CGContextDrawImage (cgctx, rect, inImage);
// Now we can get a pointer to the image data associated with the bitmap
// context.
unsigned char *data = {0};
data=(unsigned char*) calloc(CGImageGetHeight(inImage) * CGImageGetWidth(inImage) , CGBitmapContextGetHeight(cgctx)*CGBitmapContextGetWidth(cgctx));
data= CGBitmapContextGetData (cgctx);
if( data !=NULL ) {
//offset locates the pixel in the data from x,y.
//4 for 4 bytes of data per pixel, w is width of one row of data.
int offset = 4*((w*round(point.y))+round(point.x));
// NSLog(@"%s111111",data);
int alpha = data[offset]; /////// EXC_BAD_ACCESS(CODE=1,address=0x41f6864)
int red = data[offset+1];
int green = data[offset+2];
int blue = data[offset+3];
//NSLog(@"offset: %i colors: RGB A %i %i %i %i",offset,red,green,blue,alpha);
color = [UIColor colorWithRed:(red/255.0f) green:(green/255.0f) blue:(blue/255.0f) alpha:(alpha/255.0f)];
}
// When finished, release the context
//CGImageRelease(*data);
CGContextRelease(cgctx);
// Free image data memory for the context
if (data)
{
free(data);
}
}
@catch (NSException *exception) {
}
return color;
}
您的代码中的内存管理似乎是错误的:
声明data
并毫无意义地为其分配一个值:
unsigned char *data = {0};
分配一个内存块并将其引用存储在data
-覆盖无意义的初始化:
data = (unsigned char *)calloc(CGImageGetHeight(inImage) * CGImageGetWidth(inImage), CGBitmapContextGetHeight(cgctx) * CGBitmapContextGetWidth(cgctx));
现在获取对另一个内存块的引用,并将其存储在data
,而放弃对calloc
块的引用:
data = CGBitmapContextGetData (cgctx);
做一些其他的事情,然后释放您没有calloc
的块:
free(data);
如果要分配自己的内存缓冲区,则应将其传递给CGBitmapContextCreate
,但是如果您使用的是iOS 4+,则无需分配自己的缓冲区。
至于内存访问错误,您不检查point
的值,并且您的计算似乎会产生不正确的offset
值。 添加对point
和offset
值的检查,如果它们超出范围,则应采取适当的措施(您将不得不决定应采取的措施)。
HTH
该问题可能是由导致point
是出图像的rect
,所以你可以使用
try{
int offset = 4*((w*round(point.y))+round(point.x));
int alpha = data[offset];
int red = data[offset+1];
int green = data[offset+2];
int blue = data[offset+3];
color = [UIColor colorWithRed:(red/255.0f) green:(green/255.0f) blue:(blue/255.0f)
alpha:(alpha/255.0f)];
}catch(NSException e){
}
避免EXC_BAD_ACCESS
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