iOS - How To Draw Point On A Line In Which The User Touches When Dragging - ios

Question

I have a rectangular view which contains vertical thin lines in which I drew programatically.
This is the code I used to draw the lines:
- (void)drawLines
{
CGFloat spacing = _bgView.frame.size.width / 11.0f;
for(int i = 1; i < 11; i++)
{
UIView *line = [[UIView alloc] initWithFrame:CGRectMake((CGFloat)(i * spacing), 0, 1, _bgView.frame.size.height)];
line.backgroundColor = [UIColor whiteColor];
line.tag = i;
[_bgView addSubview:line];
}
}
The lines are separated by equally distributed spaces calculated from the width of the rectangular view(_bgView).
Here's an overview of what it looks like:
When the user performs a drag in the rectangular view, and when his/her finger passes through or touches a line, a dot will be drawn on that specific point.
Here's the code that detects the point of touch of the user on the line, and draws a dot on that point.
- (IBAction)drawDots:(id)sender
{
UIPanGestureRecognizer *pan = (UIPanGestureRecognizer *)sender;
CGPoint pannedPoint = [pan locationInView:_bgView];
for (UIView *subview in _bgView.subviews)
{
if (CGRectContainsPoint(subview.frame, pannedPoint) && subview.tag > 0)
{
NSLog(#"Point x:%.2f y:%.2f TAG:%i", pannedPoint.x, pannedPoint.y, subview.tag);
UIView *point = [[UIView alloc] initWithFrame:CGRectMake(pannedPoint.x - 2.5, pannedPoint.y - 2.5, 5, 5)];
point.backgroundColor = [UIColor redColor];
[_bgView addSubview:point];
}
}
}
Now, if the user pans really fast, this will be the result:
As can be seen, only some points are drawn, that's why there are a lot of missing dots on the other lines.
This should be expected result:
But, this happens only when the user pans super slow.
How can I draw the points in the lines intercepted by the touch of the user even if his finger moved really fast?
Thanks!

Answer 1

Instead of pan gestures you should use UIResponder methods to detect user touches:
- touchesBegan:withEvent:
- touchesMoved:withEvent:
- touchesEnded:withEvent:
- touchesCancelled:withEvent:
The second method - touchesMoved:withEvent: calls when user keeps moving its finger through the screen, so you can get its finger location:
UITouch *touch = [[event allTouches] anyObject];
CGPoint touchLocation = [touch locationInView:touch.view];
Then just add your detection logic.
Check the docs for more details:
https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIResponder_Class/

Answer 2

please refer this code
for your requirement
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
// NSLog(#"DEBUG: Touches moved" );
[super touchesMoved:touches withEvent:event];
if ([[event allTouches] count] > 1) {
} else {
UITouch *touch = [[event allTouches] anyObject];
UIView *view = touch.view;
NSLog(#"DEBUG: Touches Moved");
CGPoint location = [touch locationInView:self.bgView];
for (UIView *subview in _bgView.subviews)
{
if (CGRectContainsPoint(subview.frame, location) && subview.tag > 0) {
NSLog(#"Point x:%.2f y:%.2f TAG:%i", location.x, location.y, subview.tag);
UIView *point = [[UIView alloc] initWithFrame:CGRectMake(location.x - 2.5, location.y - 2.5, 5, 5)];
point.backgroundColor = [UIColor redColor];
[_bgView addSubview:point];
}
}
}
}
Will help you