IOS：用手指画一条线

-(void)intializeDrawImage
{
    drawImage = [[UIImageView alloc]initWithFrame:CGRectMake(0,100,320,320)];
   [drawImage setBackgroundColor:[UIColor purpleColor]];
   [drawImage setUserInteractionEnabled:YES];
   [self.view addSubview:drawImage];
}
 - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSLog(@"touchesBegan");
    UITouch *touch = [touches anyObject];
    CGPoint p = [touch locationInView:drawImage];
    startPoint = p;
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSLog(@"touchesMoved");
    UITouch *touch = [touches anyObject];
    CGPoint p = [touch locationInView:drawImage];
    [self drawLineFrom:startPoint endPoint:p];
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    [self touchesMoved:touches withEvent:event];
}

- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
{
    [self touchesEnded:touches withEvent:event];
}

-(void)drawLineFrom:(CGPoint)from endPoint:(CGPoint)to
{
    drawImage.image = [UIImage imageNamed:@""];

    UIGraphicsBeginImageContext(drawImage.frame.size);
    [drawImage.image drawInRect:CGRectMake(0,drawImage.frame.size.width,drawImage.frame.size.height)];
    [[UIColor greenColor] set];
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(),5.0f);
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(),from.x,from.y);
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(),to.x,to.y);

    CGContextStrokePath(UIGraphicsGetCurrentContext());

    drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
 }