Making one slate in XCode - iphone

Question

I am beginning developing with XCode, and I am starting doing some exercises and practises. I am trying to do an easy one, one drawing example in iPhone, an slate with one touch event, but I am doing something wrong; I am a little bit lost.
I create my HDPizarra class and I am triying to keep the moves. I have got one Erase button, with one IBAction that must clean the slate and restart the view; I put the lines in red colour and of 2 of width and I put the touch LocationInView of star and end. But it doesn’t go; it starts the view but when I touch the sreen nothing happens. This is the code:
-(IBAction)borrar: (id)sender
{
[lineas removeAllObjects];
}
- (id)initWithFrame: (CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
}
return self;
}
-(NSMutableArray *)lineas{
if (_lineas == nil) {
_lineas = [NSMutableArray new];
}
return _lineas;
}
- (void)drawRect: (CGRect)rect
{
if (!lineas) {
lineas = [[NSMutableArray alloc] initWithCapacity:0];
}
CGContextRef contexto = UIGraphicsGetCurrentContext();
UIColor * rojo = [UIColor redColor];
CGContextSetStrokeColorWithColor(contexto, rojo.CGColor);
CGContextSetLineWidth(contexto, 2);
CGContextMoveToPoint(contexto, inicio.x, inicio.y);
CGContextAddLineToPoint(contexto, fin.x, fin.y);
CGContextStrokePath(contexto);
}
-(void)touchesBegan: (NSSet *)touches withEvent: (UIEvent *)event{
UITouch * touch = [touches anyObject];
inicio = [touch locationInView:self];
fin = [touch locationInView:self];
[self setNeedsDisplay];
}
-(void)touchesMoved: (NSSet *)touches withEvent: (UIEvent *)event{
UITouch * touch = [touches anyObject];
fin = [touch locationInView:self];
HDLinea * linea = [[HDLinea alloc] initWithRect:CGRectMake(inicio.x, inicio.y, fin.x, fin.y)];
[self.lineas addObject: linea];
inicio.x = fin.x;
inicio.y = fin.y;
[self setNeedsDisplay];
}
The moves are from an HDLinea object, in one NSMutableArray; the code of .h is:
#import <Foundation/Foundation.h>
#interface HDLinea : NSObject
#property (readwrite) CGRect puntos;
-(id) initWithRect: (CGRect) puntos;
#end
And the one of the implementation is:
#import "HDLinea.h"
#implementation HDLinea
#synthesize puntos = _puntos;
- (id)initWithRect: (CGRect)puntos
{
self = [super init];
if (self) {
self.puntos = puntos;
}
return self;
}
#end
Any idea? Thanks a lot!!