Cell stops responding to selection after pan - ios

Question

The Problem:
After I finish a pan gesture, the cell under the initiating tap no longer responds to selection. didSelectItemAtIndexPath will fire when tapping other cells, but not the cell that was under the pan gesture.
How can I get that cell to respond to touch input again? Alternatively, how can I check if that cell is stuck responding to an event?
Background:
I have a UICollectionView with a bunch of cells. Tapping a cell in this collection view fires didSelectItemAtIndexPath.
The collection view has a pan gesture recognizer. Panning creates an image of the view and translates it around the screen. The collection view is left underneath the other views for the duration of the pan gesture.
Theories:
It's possible that the selection is never completing due to the pan. Maybe there's a touch event hanging around in the UI. If I could clear it, maybe the cell would respond again. I tried setting [panHandler setCancelsTouchesInView:YES], but it didn't change anything.
Update 1:
In the comments, a couple people suggested that the image may be hanging around and blocking the touch. In the completion block passed to animateWithDuration, I have the following lines:
[self.regionScreenshot removeFromSuperview];
self.regionScreenshot = nil;
I verified that these lines are executed.
Another factor that leads me to believe that that is not the issue is that, of all the cells, only ones that have been used to drag are affected. Surrounding cells still respond.
Update 2: Code & Gif
- (IBAction)handlePanFrom:(UIPanGestureRecognizer*)recognizer
{
CGPoint translation = [recognizer translationInView:recognizer.view];
float transparencyLevel = 0.85;
if (recognizer.state == UIGestureRecognizerStateBegan)
{
SFCYRegion* centerRegion = self.region;
//North
if (centerRegion.regionToNorth != nil)
{
self.region = centerRegion.regionToNorth;
[self reloadRegion];
self.regionToNorthScreenshot = [self.collectionView snapshotViewAfterScreenUpdates:YES];
}
else
{
self.regionToNorthScreenshot = [[UIView alloc] init];
self.regionToNorthScreenshot.backgroundColor = [UIColor darkGrayColor];
}
[self.view.superview addSubview:self.regionToNorthScreenshot];
self.regionToNorthScreenshot.alpha = transparencyLevel;
self.regionToNorthScreenshot.frame = northFrame;
//East
if (centerRegion.regionToEast != nil)
{
self.region = centerRegion.regionToEast;
[self reloadRegion];
self.regionToEastScreenshot = [self.collectionView snapshotViewAfterScreenUpdates:YES];
}
else
{
self.regionToEastScreenshot = [[UIView alloc] init];
self.regionToEastScreenshot.backgroundColor = [UIColor darkGrayColor];
}
[self.view.superview addSubview:self.regionToEastScreenshot];
self.regionToEastScreenshot.alpha = transparencyLevel;
self.regionToEastScreenshot.frame = eastFrame;
//South
if (centerRegion.regionToSouth != nil)
{
self.region = centerRegion.regionToSouth;
[self reloadRegion];
self.regionToSouthScreenshot = [self.collectionView snapshotViewAfterScreenUpdates:YES];
}
else
{
self.regionToSouthScreenshot = [[UIView alloc] init];
self.regionToSouthScreenshot.backgroundColor = [UIColor darkGrayColor];
}
[self.view.superview addSubview:self.regionToSouthScreenshot];
self.regionToSouthScreenshot.alpha = transparencyLevel;
self.regionToSouthScreenshot.frame = southFrame;
//West
if (centerRegion.regionToWest != nil)
{
self.region = centerRegion.regionToWest;
[self reloadRegion];
self.regionToWestScreenshot = [self.collectionView snapshotViewAfterScreenUpdates:YES];
}
else
{
self.regionToWestScreenshot = [[UIView alloc] init];
self.regionToWestScreenshot.backgroundColor = [UIColor darkGrayColor];
}
[self.view.superview addSubview:self.regionToWestScreenshot];
self.regionToWestScreenshot.alpha = transparencyLevel;
self.regionToWestScreenshot.frame = westFrame;
//Northeast
if (centerRegion.regionToNorth != nil && centerRegion.regionToNorth.regionToEast != nil)
{
self.region = centerRegion.regionToNorth.regionToEast;
[self reloadRegion];
self.regionToNortheastScreenshot = [self.collectionView snapshotViewAfterScreenUpdates:YES];
}
else
{
self.regionToNortheastScreenshot = [[UIView alloc] init];
self.regionToNortheastScreenshot.backgroundColor = [UIColor darkGrayColor];
}
[self.view.superview addSubview:self.regionToNortheastScreenshot];
self.regionToNortheastScreenshot.alpha = transparencyLevel;
self.regionToNortheastScreenshot.frame = northeastFrame;
//Southeast
if (centerRegion.regionToSouth != nil && centerRegion.regionToSouth.regionToEast != nil)
{
self.region = centerRegion.regionToSouth.regionToEast;
[self reloadRegion];
self.regionToSoutheastScreenshot = [self.collectionView snapshotViewAfterScreenUpdates:YES];
}
else
{
self.regionToSoutheastScreenshot = [[UIView alloc] init];
self.regionToSoutheastScreenshot.backgroundColor = [UIColor darkGrayColor];
}
[self.view.superview addSubview:self.regionToSoutheastScreenshot];
self.regionToSoutheastScreenshot.alpha = transparencyLevel;
self.regionToSoutheastScreenshot.frame = southeastFrame;
//Southwest
if (centerRegion.regionToSouth != nil && centerRegion.regionToSouth.regionToWest != nil)
{
self.region = centerRegion.regionToSouth.regionToWest;
[self reloadRegion];
self.regionToSouthwestScreenshot = [self.collectionView snapshotViewAfterScreenUpdates:YES];
}
else
{
self.regionToSouthwestScreenshot = [[UIView alloc] init];
self.regionToSouthwestScreenshot.backgroundColor = [UIColor darkGrayColor];
}
[self.view.superview addSubview:self.regionToSouthwestScreenshot];
self.regionToSouthwestScreenshot.alpha = transparencyLevel;
self.regionToSouthwestScreenshot.frame = southwestFrame;
//Northwest
if (centerRegion.regionToNorth != nil && centerRegion.regionToNorth.regionToWest != nil)
{
self.region = centerRegion.regionToNorth.regionToWest;
[self reloadRegion];
self.regionToNorthwestScreenshot = [self.collectionView snapshotViewAfterScreenUpdates:YES];
}
else
{
self.regionToNorthwestScreenshot = [[UIView alloc] init];
self.regionToNorthwestScreenshot.backgroundColor = [UIColor darkGrayColor];
}
[self.view.superview addSubview:self.regionToNorthwestScreenshot];
self.regionToNorthwestScreenshot.alpha = transparencyLevel;
self.regionToNorthwestScreenshot.frame = northwestFrame;
//Self
self.region = centerRegion;
[self reloadRegion];
self.regionScreenshot = [self.collectionView snapshotViewAfterScreenUpdates:YES];
self.regionScreenshot.frame = mainFrame;
self.regionScreenshot.center = mainFrameCenter;
[self.view.superview addSubview:self.regionScreenshot];
self.collectionView.alpha = 0;
}
else if (recognizer.state == UIGestureRecognizerStateChanged)
{
//Track the movement:
self.regionScreenshot.center = [self movePoint:mainFrameCenter
byX:translation.x andY:translation.y];
self.regionToNorthScreenshot.center = [self movePoint:northFrameCenter
byX:translation.x andY:translation.y];
self.regionToEastScreenshot.center = [self movePoint:eastFrameCenter
byX:translation.x andY:translation.y];
self.regionToSouthScreenshot.center = [self movePoint:southFrameCenter
byX:translation.x andY:translation.y];
self.regionToWestScreenshot.center = [self movePoint:westFrameCenter byX:translation.x andY:translation.y];
self.regionToNortheastScreenshot.center = [self movePoint:northeastFrameCenter
byX:translation.x andY:translation.y];
self.regionToSoutheastScreenshot.center = [self movePoint:southeastFrameCenter
byX:translation.x andY:translation.y];
self.regionToSouthwestScreenshot.center = [self movePoint:southwestFrameCenter
byX:translation.x andY:translation.y];
self.regionToNorthwestScreenshot.center = [self movePoint:northwestFrameCenter
byX:translation.x andY:translation.y];
//[recognizer setTranslation:CGPointMake(0, 0) inView:self.view];
}
else if (recognizer.state == UIGestureRecognizerStateEnded)
{
SFCYRegion* newRegion;
UIView* viewToMoveToCenter;
CGSize slideVector;
NSInteger movedByX = 0;
NSInteger movedByY = 0;
float thresholdPercentage = 0.4;
BOOL isOverThresholdToNorth = translation.y > (mainFrame.size.height * thresholdPercentage);
BOOL isOverThresholdToSouth = -translation.y > (mainFrame.size.height * thresholdPercentage);
BOOL isOverThresholdToEast = -translation.x > (mainFrame.size.width * thresholdPercentage);
BOOL isOverThresholdToWest = translation.x > (mainFrame.size.width * thresholdPercentage);
if (isOverThresholdToNorth && self.region.regionToNorth != nil)
{
movedByY = -1;
if (isOverThresholdToEast && self.region.regionToNorth.regionToEast != nil)
{
//Northeast
newRegion = self.region.regionToNorth.regionToEast;
viewToMoveToCenter = self.regionToNortheastScreenshot;
movedByX = 1;
}
else if (isOverThresholdToWest && self.region.regionToNorth.regionToWest != nil)
{
//Northwest
newRegion = self.region.regionToNorth.regionToWest;
viewToMoveToCenter = self.regionToNorthwestScreenshot;
movedByX = -1;
}
else
{
//North
newRegion = self.region.regionToNorth;
viewToMoveToCenter = self.regionToNorthScreenshot;
}
}
else if (isOverThresholdToSouth && self.region.regionToSouth != nil)
{
movedByY = 1;
if (isOverThresholdToEast && self.region.regionToSouth.regionToEast != nil)
{
//Southeast
newRegion = self.region.regionToSouth.regionToEast;
viewToMoveToCenter = self.regionToSoutheastScreenshot;
movedByX = 1;
}
else if (isOverThresholdToWest && self.region.regionToSouth.regionToWest != nil)
{
//Southwest
newRegion = self.region.regionToSouth.regionToWest;
viewToMoveToCenter = self.regionToSouthwestScreenshot;
movedByX = -1;
}
else
{
//South
newRegion = self.region.regionToSouth;
viewToMoveToCenter = self.regionToSouthScreenshot;
}
}
else if (isOverThresholdToEast && self.region.regionToEast != nil)
{
//East
newRegion = self.region.regionToEast;
viewToMoveToCenter = self.regionToEastScreenshot;
movedByX = 1;
}
else if (isOverThresholdToWest && self.region.regionToWest != nil)
{
//West
newRegion = self.region.regionToWest;
viewToMoveToCenter = self.regionToWestScreenshot;
movedByX = -1;
}
else
{
//None, so return to start:
newRegion = self.region;
viewToMoveToCenter = self.regionScreenshot;
}
slideVector = CGSizeMake(mainFrameCenter.x - viewToMoveToCenter.center.x,
mainFrameCenter.y - viewToMoveToCenter.center.y);
[UIView animateWithDuration:0.2
animations:^
{
viewToMoveToCenter.alpha = 1;
if (![self.regionScreenshot isEqual:viewToMoveToCenter])
{
self.regionScreenshot.alpha = transparencyLevel;
}
self.regionScreenshot.center = [self movePoint:self.regionScreenshot.center
byX:slideVector.width andY:slideVector.height];
self.regionToNorthScreenshot.center = [self movePoint:self.regionToNorthScreenshot.center
byX:slideVector.width andY:slideVector.height];
self.regionToEastScreenshot.center = [self movePoint:self.regionToEastScreenshot.center
byX:slideVector.width andY:slideVector.height];
self.regionToSouthScreenshot.center = [self movePoint:self.regionToSouthScreenshot.center
byX:slideVector.width andY:slideVector.height];
self.regionToWestScreenshot.center = [self movePoint:self.regionToWestScreenshot.center
byX:slideVector.width andY:slideVector.height];
self.regionToNortheastScreenshot.center = [self movePoint:self.regionToNortheastScreenshot.center
byX:slideVector.width andY:slideVector.height];
self.regionToSoutheastScreenshot.center = [self movePoint:self.regionToSoutheastScreenshot.center
byX:slideVector.width andY:slideVector.height];
self.regionToSouthwestScreenshot.center = [self movePoint:self.regionToSouthwestScreenshot.center
byX:slideVector.width andY:slideVector.height];
self.regionToNorthwestScreenshot.center = [self movePoint:self.regionToNorthwestScreenshot.center
byX:slideVector.width andY:slideVector.height];
}
completion:^(BOOL finished)
{
if (finished)
{
//Remove the old views:
self.collectionView.alpha = 1;
[self.regionScreenshot removeFromSuperview];
[self.regionToNorthScreenshot removeFromSuperview];
[self.regionToEastScreenshot removeFromSuperview];
[self.regionToSouthScreenshot removeFromSuperview];
[self.regionToWestScreenshot removeFromSuperview];
[self.regionToNortheastScreenshot removeFromSuperview];
[self.regionToSoutheastScreenshot removeFromSuperview];
[self.regionToSouthwestScreenshot removeFromSuperview];
[self.regionToNorthwestScreenshot removeFromSuperview];
self.regionScreenshot = nil;
self.regionToNorthScreenshot = nil;
self.regionToEastScreenshot = nil;
self.regionToSouthScreenshot = nil;
self.regionToWestScreenshot = nil;
self.regionToNortheastScreenshot = nil;
self.regionToSoutheastScreenshot = nil;
self.regionToSouthwestScreenshot = nil;
self.regionToNorthwestScreenshot = nil;
}
}];
if (![self.regionScreenshot isEqual:viewToMoveToCenter])
{
self.region = newRegion;
[self reloadRegion];
[self movedRegionByX:movedByX andY:movedByY];
}
[recognizer setTranslation:CGPointMake(0, 0) inView:self.view];
}
}
Here is an image demonstrating the issue. I perform a selection on the "Suburb" cell, then pan, and then am no longer able to perform a selection on that cell, but can still select others:
Update 3: All Gestures
This occurs when I do swipe gestures and pinch gestures as well. If I add in two-finger swipe gestures, both cells under the origin points are affected.

Answer 1

Make sure that regionScreenshot and any other view's you add to the view hierarchy have userInteractionEnabled set to NO.
Also set your cell and its content's clipsToBounds set to YES. Sometimes views look OK but actually they are "much smaller than they appear".

Answer 2

When I was panning, I called [self.collectionView reloadData] in the process of generating the screenshots to use for the adjacent regions. Reloading the cells while a gesture was active seemed to interfere with that individual cell's ability to handle gestures.
As a workaround, I instead added a second, hidden UICollectionView to the controller and load the data into that view and take screenshots of it instead of the main view. The main collection view never has to reload the data until the gestures are complete and a new region is selected.
UIView* aScreenshot = [self.secondaryCollectionView snapshotViewAfterScreenUpdates:YES];