Drawing a line between the previous end point to next start point - iphone

Question

i'm stuck at this problem. I need to draw a line between the previous end point to next start point. My code for drawing a line between 2 points is
- (void)drawRect:(CGRect)rect
{
CGContextRef c=UIGraphicsGetCurrentContext();
CGContextSetLineWidth(c, 4.0);
CGFloat red[4]={0.0f, 0.0f, 0.0f, 1.0f};
CGContextSetStrokeColor(c, red);
CGContextBeginPath(c);
CGContextMoveToPoint(c, 50.0f, 50.0f);
CGContextAddLineToPoint(c, 100.0f, 100.0f);
CGContextStrokePath(c) ;
}
How can i give multiple points, so that i can it shows like a graph.
Thanks in advance

Answer 1

On a side note, Apple prefers that you use the higher UIKit methods instead of the Core Graphics calls for simple stuff like drawing lines and curves, so you could rewrite your method like this:
[[UIColor redColor] setStroke];
UIBezierPath *linePath = [UIBezierPath bezierPath];
[linePath moveToPoint:CGPointMake(50.0, 50.0)];
[linePath addLineToPoint:CGPointMake(100.0, 100.0)];
[linePath setLineWidth:4.0];
[linePath stroke];

Answer 2

Just add more CGContextAddLineToPoint calls
- (void)drawRect:(CGRect)rect
{
CGContextRef c=UIGraphicsGetCurrentContext();
CGContextSetLineWidth(c, 4.0);
CGFloat red[4]={0.0f, 0.0f, 0.0f, 1.0f};
CGContextSetStrokeColor(c, red);
CGContextBeginPath(c);
CGContextMoveToPoint(c, 50.0f, 50.0f);
CGContextAddLineToPoint(c, 100.0f, 100.0f);
CGContextAddLineToPoint(c, 120.0f, 80.0f);
CGContextAddLineToPoint(c, 140.0f, 120.0f);
CGContextAddLineToPoint(c, 160.0f, 80.0f);
...
CGContextStrokePath(c) ;
}

Answer 3

Jus a little correction to your code:
-(void)drawLineFromPoint:(CGPoint)startPoint toPoint:(CGPoint)endPoint{
UIGraphicsBeginImageContext(YOUR_IMAGEVIEW.image.size);
[YOUR_IMAGEVIEW.image drawInRect:CGRectMake(0, 0, YOUR_IMAGEVIEW.image.size.width, YOUR_IMAGEVIEW.image.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 0.0, 0.0, 0.0, 1.0);
CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), startPoint.x, startPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), endPoint.x, endPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
[YOUR_IMAGEVIEW setImage:UIGraphicsGetImageFromCurrentImageContext()];
UIGraphicsEndImageContext();
}
YOUR_IMAGEVIEW is an outlet to your imageview you are drawing on.
As you can see - you just have to send to this method your start point and the end one! Easy as 1-2-3.
EDIT 1
How to use it? Declare a global CGPoint "startPoint";
Then say:
//___________________________________________________
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [touches anyObject];
startPoint = [touch locationInView:YOUR_IMAGEVIEW];
}
//___________________________________________________
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
UITouch *touch = [touches anyObject];
CGPoint nextPoint = [touch locationInView:YOUR_IMAGEVIEW];
[self drawLineFromPoint:startPoint toPoint:nextPoint];
startPoint = nextPoint;
}
EDIT 2
Here is another way to draw your points:
- (void)drawGraphMethod{
NSMutableArray *pointsArr = [[[NSMutableArray alloc]init]autorelease];
//now you should add the needed points to your array
//I have no idea what graph do you have, so I just
//put there some random points that will look like a graph
[pointsArr addObject:[NSValue valueWithCGPoint:CGPointMake(30.0, 10.0)]];
[pointsArr addObject:[NSValue valueWithCGPoint:CGPointMake(40.0, 26.0)]];
[pointsArr addObject:[NSValue valueWithCGPoint:CGPointMake(70.0, 55.0)]];
[pointsArr addObject:[NSValue valueWithCGPoint:CGPointMake(80.0, 88.0)]];
[pointsArr addObject:[NSValue valueWithCGPoint:CGPointMake(90.0, 33.0)]];
[pointsArr addObject:[NSValue valueWithCGPoint:CGPointMake(130.0, 100.0)]];
//well, you can store only objects, that's why I used NSValue.
//it's not hard to cenvert it back
//now parse the array
for (int i = 0; i < pointsArr.count-1; i++) {
CGPoint startPoint = [[pointsArr objectAtIndex:i] CGPointValue];
CGPoint nextPoint = [[pointsArr objectAtIndex:i+1] CGPointValue];
[self drawLineFromPoint:startPoint toPoint:nextPoint];
}
}