Draw stuff on touch objective c - objective-c

Question

hy,
How can i make something that changes color when i touch it in objective c, i want the whole screen to be touchable and want to draw stuff on it with finger.
Everywhere i touch it should change the color.
Whats the best way to do it? I already have touchesMoved implemented to get the coordinates of the touch.
UITouch * touch = [touches anyObject];
CGPoint pos = [touch locationInView: [UIApplication sharedApplication].keyWindow];
Any example code would be nice thanks.
thank you in advance,
i have the following code but it doesnt print anything where i touch
-(void)setPaths:(NSMutableArray *)paths
{
self.paths =[[NSMutableArray alloc]init];
}
-(void)setAPath:(UIBezierPath *)aPath
{
self.aPath=[UIBezierPath bezierPath];
}
-(void) drawRect:(CGRect)rect{
[super drawRect:rect];
[[UIColor blackColor] set];
for (UIBezierPath *path in paths) {
[path stroke];
}
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
[self.paths addObject:self.aPath];
//self.aPath=[UIBezierPath bezierPath];
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch * touch = [touches anyObject];
CGPoint pos = [touch locationInView: [UIApplication sharedApplication].keyWindow];
[self.aPath addLineToPoint:[touch locationInView:self]];
// [self.aPath addLineToPoint:[touch locationInView:touch]];
NSLog(#"Position of touch: %.3f, %.3f", pos.x, pos.y);
}
#end

Answer 1

When your touch starts, create a UIBezierPath:
self.myPath = [UIBezierPath bezierPath];
Then, every time the touches moves, add a point to the path:
[self.myPath addLineToPoint:[touch locationInView:self]];
Once your touch has ended, in your drawRect just draw the path:
-(void) drawRect:(CGRect)rect{
[super drawRect:rect];
[[UIColor blueColor] set];
for (UIBezierPath *path in paths) {
[path stroke];
}
}
Find all the doc here:
UIBezierPath Class Reference

Answer 2

Maybe you're going to change your drawRect: method. insert these 2 lines:
[[UIColor blackColor] setStroke];
[path stroke];
and you should add [self setNeedsDisplay]; after you've added a line inside touchesMoved:
I just passed following tutorial, it should solve your problem. It also explains how you can improve your code so it won't get too lazy if you're drawing longer lines:
http://mobile.tutsplus.com/tutorials/iphone/ios-sdk_freehand-drawing/