Where's my Bezier path? - ios

Question

I am trying to draw a Bezier path, an arc of a given angle, in response to a pan gesture. Here's what I have inside the function called by the pan gesture:
UIGraphicsBeginImageContext(self.frame.size);
UIBezierPath *path = [self createArcPath];
[[UIColor blackColor] setStroke];
[[UIColor redColor] setFill];
CGContextRef *ref = UIGraphicsGetCurrentContext();
path.lineWidth = 5;
[path fill];
[path stroke];
UIGraphicsEndImageContext();
And here is createArcPath:
- (UIBezierPath *)createArcPath
{
UIBezierPath *aPath = [UIBezierPath bezierPathWithArcCenter:CGPointMake(150, 150)
radius:75
startAngle:0
endAngle:DEGREES_TO_RADIANS(135)
clockwise:YES];
return aPath;
}
I don't get an error, but I just don't get anything on my screen relating to the arc. What am I missing? This is in a method of a UIView subclass.
I also tried the following method in - (id)initWithFrame:
UIColor *color =[UIColor redColor];
UIGraphicsBeginImageContext(self.frame.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, width);
CGContextSetFillColorWithColor(context, color.CGColor);
CGContextSetStrokeColorWithColor(context, color.CGColor);
CGRect myOval = {100, 100, self.radius, self.radius};
CGContextAddEllipseInRect(context, myOval);
UIGraphicsEndImageContext();
I also don't see anything. What am I missing? Can these methods not be called from a UIView?

Answer 1

The UIGraphicsBeginImageContext/UIGraphicsEndImageContext calls create an off-screen context that you can draw into, then extract an image from. Since it's an off-screen context nothing shows on the screen.
What you probably want to do is create a custom subclass of UIView that overrides drawRect. In your code that responds to user gestures, change the data structure(s) that represent your drawing, then call setNeedsDisplay to trigger the system to ask your view to redraw itself by calling your drawRect method.
As an alternative you can set up your custom view to install a CAShapeLayer in the view, then change the path on the layer, then call setNeedsDisplay on the layer.