Drawing to a view from a function - objective-c

Question

I can draw a line by placing the following into a UIView and connecting it to a storyboard View.
- (void)drawRect:(CGRect)rect {
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, 5.0);
CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
CGFloat components[] = {0.0, 0.0, 1.0, 1.0};
CGColorRef color = CGColorCreate(colorspace, components);
CGContextSetStrokeColorWithColor(context, color);
CGContextMoveToPoint(context, 0, 0);
CGContextAddLineToPoint(context, 10, 50);
CGContextStrokePath(context);
CGColorSpaceRelease(colorspace);
CGColorRelease(color);
}
However, what I want to do is to draw a line whenever a button is pressed. To do this I assume I need to write some code into an IBAction. My problem is that I cannot simply place the above code into the IBAction as it gives me an error.
- (IBAction)draw:(id)sender{
//Place code here
}
My question is, how can I draw a line each time the button is pressed?
How do I connect similar code to draw a different line that will be triggered when I press a button

Answer 1

To draw on a UIView you have to subclass your UIView
In .h
#MyCustomView : UIView {
}
#end
in .m
#implementation MyCustomView
- (void) drawRect: (CGRect) rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, 5.0);
CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
CGFloat components[] = {0.0, 0.0, 1.0, 1.0};
CGColorRef color = CGColorCreate(colorspace, components);
CGContextSetStrokeColorWithColor(context, color);
CGContextMoveToPoint(context, 0, 0);
CGContextAddLineToPoint(context, 10, 50);
CGContextStrokePath(context);
CGColorSpaceRelease(colorspace);
CGColorRelease(color);
}
In your ViewController
-(void)methodCallCustomView{
}
- (IBAction)draw:(id)sender{
[self methodCallCustomView];
}

Answer 2

So you want the drawRect: method to be called when you press a button? If so, send the message setNeedsDisplay to the view that has the drawRect: code.