UIPanGestureRecognizer in a UITableViewCell not recognizing left Pan - ios

Question

Right now I am developing an iPad app that uses a subclass of UITableviewCell that uses UIPanGestureRecognizer to slide left and right, However it only slides right and dosent slide left... This is the code I am usuing:
- (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier
{
self = [super initWithStyle:style reuseIdentifier:reuseIdentifier];
if (self)
{
// Initialization code
UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:#selector(handlePan:)];
pan.delegate = self;
[self addGestureRecognizer:pan];
}
return self;
}
This is my handlePan: method,
CGPoint translation = [gesture locationInView:self];
self.center = CGPointMake(self.center.x + translation.x,
self.center.y);
if (self.center.x > 700) {
NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:self.tag],#"number",nil];
[[NSNotificationCenter defaultCenter] postNotificationName:#"right" object:nil userInfo:dic];
dic = nil;
}
if (self.center.x < 0){
NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:self.tag],#"number",nil];
[[NSNotificationCenter defaultCenter] postNotificationName:#"left" object:nil userInfo:dic];
dic = nil;
NSLog(#"Left Called");
}
[gesture setTranslation:CGPointZero inView:self];
No matter what I try, i cant seem to get the console to say "Left Called" , i.e. The cell slides left. I am really struggling with this issue and would appreciate any help at all.

Answer 1

The trick is to react to the changed state of the pan, and the center calculation can be much simpler...
- (void)handlePan:(UIPanGestureRecognizer *)gesture {
if ((gesture.state == UIGestureRecognizerStateChanged) ||
(gesture.state == UIGestureRecognizerStateEnded)) {
CGPoint newCenter = CGPointMake([gesture locationInView:self.superview].x, self.center.y);
self.center = newCenter;
// To determine the direction of the pan, check the sign of translation in view.
// This supplies the cumulative translation...
if ([gesture translationInView:self.superview].x > 0) {
NSLog(#">>>");
} else {
NSLog(#"<<<");
}
}
}

Answer 2

I think the way that you are determining left/right might be flawed.
CGPoint translation = [gesture locationInView:self];
self.center = CGPointMake(self.center.x + translation.x,
self.center.y);
self.center.x will always be positive since "translation" is the location in the view which is positive.
What you probably want to keep track of the original touch position and then compare that with the location when swiping/moving. Try something like this:
- (void)handlePan:(UIPanGestureRecognizer *)panRecognizer {
if (panRecognizer.state == UIGestureRecognizerStateBegan)
{
// create a local property for the original point and assign the position on first touch
self.originalPanTouchPoint = [panRecognizer locationInView:self.view];
// create a local property for cell's center prior to pan
self.initialCellCenter = self.center;
} else {
CGPoint currentTouchPoint = [panRecognizer locationInView:self.view];
CGFloat xTranslation = self.originalPanTouchPoint.x - currentTouchPoint.x;
self.center = CGPointMake(self.initialCellCenter.x + xTranslation, self.initialCellCenter.y);
}
}