Question

// CStroke.h
#import

@interface CStroke : NSObject {
    CGFloat *startX;
    CGFloat *startY;
    CGFloat *endX;
    CGFloat *endY;
    BOOL *state;
}
@property CGFloat *startX;
@property CGFloat *startY;
@property CGFloat *endX;
@property CGFloat *endY;
@property BOOL *state;
-(void)setStroke: (CGFloat *)newStartX andStartY:(CGFloat *)newStartY andEndX:(CGFloat *)newEndX andEndY:(CGFloat *)newEndY;
@end

After set up CStroke class, I am going to use it in ViewController to draw something out using CGFloat

CGFloat *startX = (CGFloat *)[[self retrieveStartCoordinateOfStroke:k whichKindOfCoorXOrY:@"X"] integerValue];
        CGFloat *startY = (CGFloat *)[[self retrieveStartCoordinateOfStroke:k whichKindOfCoorXOrY:@"Y"] integerValue];
        CGFloat *endX = (CGFloat *)[[self retrieveEndCoordinateOfStroke:k whichKindOfCoordXOrY:@"X"] integerValue];
        CGFloat *endY = (CGFloat *)[[self retrieveEndCoordinateOfStroke:k whichKindOfCoordXOrY:@"Y"] integerValue];
        CStroke *stroke = [[CStroke alloc] init];
        [stroke setStroke:startX andStartY:startY andEndX:endX andEndY:endY];

This is where I got error…I can’t figure out what happened…are they both CGFloat type…Any answer for this?
The error is incompatible type for argument 2 of ‘CGContextAddLineToPoint’ and incompatible type for argument 2 of ‘CGContextMoveToPoint’

CGContextMoveToPoint(UIGraphicsGetCurrentContext(), myStroke.startX, myStroke.startY);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), [myStroke endX], [myStroke endY]);

Answer 1

Your problem is you’re making your coordinates, pointers to CGFloat and not CGFloat types. They are not object types. CGfloat is currently, do not rely on this in the future just a type alias to float, and the functions you’re passing to eventually, expect the scalar values, not pointers.

On a secondary note, getting the current graphics context is not a cheap operation. Do it once. That is, change your code to look something like this:

CGContextRef context = UIGraphicsGetCurrentContext();

// Now pass in context where you would normally pass in UIGraphicsGetCurrentContext()