我正在尝试编写一个CGFunctionRef,它将在使用ARC的项目中充当CGShadingRef对象的着色函数我正试图将NSMutableArray(填充UIColors)传递到CGFunctionRef回调函数中。
这是我的初始化方法
- (void)initInternal {
_colors = [[NSMutableArray alloc] init];
// Creating the colors in this way ensures that the underlying color space is UIDeviceRGBColorSpace
// and thus has 4 color components: red, green, blue, alpha
[_colors addObject:[UIColor colorWithRed:1.0f green:0.0f blue:0.0f alpha:1.0f]]; // Red
[_colors addObject:[UIColor colorWithRed:0.0f green:1.0f blue:0.0f alpha:1.0f]]; // Green
[_colors addObject:[UIColor colorWithRed:0.0f green:0.0f blue:1.0f alpha:1.0f]]; // Blue
[_colors addObject:[UIColor colorWithRed:1.0f green:1.0f blue:1.0f alpha:1.0f]]; // White
[_colors addObject:[UIColor colorWithRed:0.0f green:0.0f blue:0.0f alpha:1.0f]]; // Black
// Define the shading callbacks
CGFunctionCallbacks callbacks;
callbacks.version = 0; // Defaults to 0
callbacks.evaluate = CGShadingCallback; // This is our color selection function
callbacks.releaseInfo = NULL; // Not used
// As input to our function we want 1 value in the range [0.0, 1.0].
// This is our position within the 'gradient'.
size_t domainDimension = 1;
CGFloat domain[2] = {0.0f, 1.0f};
// The output of our function is 4 values, each in the range [0.0, 1.0].
// This is our selected color for the input position.
// The 4 values are the red, green, blue and alpha components.
size_t rangeDimension = 4;
CGFloat range[8] = {0.0f, 1.0f, 0.0f, 1.0f, 0.0f, 1.0f, 0.0f, 1.0f};
// Create the shading function
_shadingFunction = CGFunctionCreate(&_colors, domainDimension, domain, rangeDimension, range, &callbacks);
}
这是我的回调方法
static void CGShadingCallback(void* info, const float* inData, float* outData) {
// Our colors
NSMutableArray* colors = (__bridge_transfer NSMutableArray*)info;
// Position within the gradient, ranging from 0.0 to 1.0
CGFloat position = *inData;
// Find the color that we want to used based on the current position;
NSUInteger colorIndex = position * [colors count];
// Account for the edge case where position == 1.0
if (colorIndex >= [colors count])
colorIndex = [colors count] - 1;
// Get our desired color from the array
UIColor* color = [colors objectAtIndex:colorIndex];
// Copy the 4 color components (red, green, blue, alpha) to outData
memcpy(outData, CGColorGetComponents(color.CGColor), 4 * sizeof(CGFloat));
}
这是我的drawRect方法
- (void)drawRect:(CGRect)rect {
CGRect b = self.bounds;
CGContextRef ctx = UIGraphicsGetCurrentContext();
// Create a simple elliptic path
CGContextAddEllipseInRect(ctx, b);
// Set the current path as the clipping path
CGContextClip(ctx);
// Create our shading using the function that was defined earlier.
CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
CGShadingRef shading = CGShadingCreateAxial(colorspace,
CGPointMake(CGRectGetMinX(b), CGRectGetMidY(b)),
CGPointMake(CGRectGetMaxX(b), CGRectGetMidY(b)),
_shadingFunction,
true,
true);
// Draw the shading
CGContextDrawShading(ctx, shading);
// Cleanup
CGShadingRelease(shading);
CGColorSpaceRelease(colorspace);
}
如果我只是在回调方法中使用\uu桥,那么
NSMutableArray*colors=((uu bridge NSMutableArray*)信息
使用EXC_BAD_访问。
如果我用桥转车,它会在
CGContextDrawShading(ctx,着色)
在drawRect中有一个EXC_BAD_访问权限。
最佳答案
创建一个数组并将该数组用作CGFunction
的上下文。
因此,当赋予函数时,需要保留该数组您可以使用__bridge_retained
关键字执行此操作:
CGFunctionCallbacks callbacks;
callbacks.version = 0;
callbacks.evaluate = CGShadingCallback;
callbacks.releaseInfo = myReleaseCallback;
_shadingFunction = CGFunctionCreate((__bridge_retained void *)_colors, domainDimension, domain, rangeDimension, range, &callbacks);
然后,不能在图形回调中的
__bridge_transfer
中使用__bridge_transfer
将值转换为一个强引用而不保留它(所有权被转移)这相当于释放数组由于回调可能被多次调用,因此这不是释放数组的正确位置。函数被破坏时必须释放数组这就是
releaseInfo
回调的目的:static void myReleaseCallback(void *info) {
CFRelease(info);
}
你也可以用一个
__bridge_transfer
的演员来做,但这不是很优雅:static void myReleaseCallback(void *info) {
NSArray *array = (__bridge_transfer NSArray *)info;
// now we need to do something with the array if we don't want a compiler warning
}
关于iphone - 将Objective-C对象传递给CGFunctionRef,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/8569431/