touchesMoved事件未获得正确的CGPoint

Question

I was trying to implement a scrollView by setting the bounds while paning the view
I was doing a test in touchesMoved :

UITouch* touch = [touches anyObject];
CGPoint pt = [touch locationInView:self];
if(pt.x - _lastPoint.x >= 0){
    NSLog(@"yep");
}
else{
    NSLog(@"nope");
    NSLog(@"%f",pt.x);
}
_lastPoint.x = pt.x;
[self setBounds:CGRectMake(self.bounds.origin.x - 1, 0,  self.frame.size.width, self.frame.size.height)];

And while I was paning in one direction(from left to right all the way ),I can always get a few bad points,here is one of the logs:

2014-04-26 14:59:41.621 LScrollView[9884:60b] yep
2014-04-26 14:59:41.638 LScrollView[9884:60b] yep
2014-04-26 14:59:41.656 LScrollView[9884:60b] yep
2014-04-26 14:59:41.673 LScrollView[9884:60b] yep
2014-04-26 14:59:41.696 LScrollView[9884:60b] yep
2014-04-26 14:59:41.713 LScrollView[9884:60b] yep
2014-04-26 14:59:41.729 LScrollView[9884:60b] yep
2014-04-26 14:59:41.762 LScrollView[9884:60b] yep
2014-04-26 14:59:41.796 LScrollView[9884:60b] nope
2014-04-26 14:59:41.797 LScrollView[9884:60b] 143.000000
2014-04-26 14:59:41.813 LScrollView[9884:60b] yep
2014-04-26 14:59:41.829 LScrollView[9884:60b] yep
2014-04-26 14:59:41.846 LScrollView[9884:60b] yep

And I also wrote a test that not changing the bounds of the view in touchesMoved and everything works fine,did I missing something?

Answer 1

There is no need to change the bounds of the view while you are dragging the finger on it. You are always making your origin 1 pixel back on left side. I mean if it is at x = 0 on next event it will be shifted to x = -1.

Till the time next event is generated and you have not dragged your finger for 1 pixel in right direction, app will return you the point which will not able to fulfil your if condition. So, remove setBounds on each dragging event or drag the finger very fast.