UIAttachmentBehavior in UITableViewCell

Question

I've added a horizontal UIPanGestureRecognizer to my tableviewcell to pan a subview of the cell, like the way the ios7 mail app does to reveal delete and more options and this works as expected

- (IBAction)slideCell:(UIPanGestureRecognizer *)sender
{

    CGPoint locationOfPan = [sender locationInView:self.tableView];
    NSIndexPath *indexPath = [self.tableView indexPathForRowAtPoint:locationOfPan];
    TestCell *cell = (TestCell *)[self.tableView cellForRowAtIndexPath:indexPath];    

    if (sender.state == UIGestureRecognizerStateChanged) {
        CGPoint translation = [sender translationInView:self.tableView];
        [cell.view setCenter:CGPointMake(cell.view.center.x + translation.x, cell.view.center.y)];
        [sender setTranslation:CGPointMake(0, 0) inView:self.tableView];
    }
}

What I would also like to do is add a UIAttachmentBehavior with an anchor point to each of my UITableViewCells so that when I pan the cell.view horizontally I feel some resistance and then when I let go, the view in the cell that was panned springs back to it's original anchor position on the x axis, is this possible to do with UIDynamics?

Also can I set one side of the cell as a boundary which prevents a user from panning the contained view beyond it?

Answer 1

So here is code to get this working, it still needs to be tweaks to get the right feel but it all works as expected

In the TestCell UITableViewCell subclass

-(void)layoutSubviews{

    [super layoutSubviews];

    self.animator = [[UIDynamicAnimator alloc] initWithReferenceView:self];

    self.attachmentBehavior = [[UIAttachmentBehavior alloc] initWithItem:self.topView attachedToAnchor:self.topView.center];
    [self.attachmentBehavior setFrequency:4.5];
    [self.attachmentBehavior setDamping:0.3];

    UIGravityBehavior *gravityBehavior = [[UIGravityBehavior alloc] initWithItems:@[self.topView]];

    //gravity direction: right
    [gravityBehavior setGravityDirection:CGVectorMake(1.0, 0.0)];

    UICollisionBehavior *collisionBehavior = [[UICollisionBehavior alloc] initWithItems:@[self.topView]];
    [collisionBehavior addBoundaryWithIdentifier:@"rightBoundary" fromPoint:CGPointMake(320.0f, 0.0f) toPoint:CGPointMake(320.0f, self.contentView.frame.size.height)];
    [self.animator addBehavior:gravityBehavior];
    [self.animator addBehavior:collisionBehavior];

}

In my tableViewController

-(BOOL)gestureRecognizerShouldBegin:(UIPanGestureRecognizer *)gestureRecognizer {
    CGPoint translation = [gestureRecognizer translationInView:self.view.superview];
    // Check for horizontal gesture
    if (fabsf(translation.x) > fabsf(translation.y)) {
        return YES;
    }else{
        return NO;
    }

}


- (IBAction)slideCell:(UIPanGestureRecognizer *)sender
{

    CGPoint locationOfPan = [sender locationInView:self.tableView];
    NSIndexPath *indexPath = [self.tableView indexPathForRowAtPoint:locationOfPan];
    TestCell *cell = (TestCell *)[self.tableView cellForRowAtIndexPath:indexPath];

    if(sender.state == UIGestureRecognizerStateBegan){

        [cell.attachmentBehavior setAnchorPoint:cell.topView.center];
        [cell.animator addBehavior:cell.attachmentBehavior];

    }

    if (sender.state == UIGestureRecognizerStateChanged) {

        CGPoint translation = [sender translationInView:self.tableView];
        [cell.attachmentBehavior setAnchorPoint:CGPointMake(cell.topView.center.x + translation.x, cell.topView.center.y)];
        [sender setTranslation:CGPointMake(0, 0) inView:self.tableView];

    }

    if (sender.state == UIGestureRecognizerStateEnded) {
        //incase pan gesture has moved off the cell
        for(TestCell *cell in [self.tableView visibleCells]){
            [cell.animator removeBehavior:cell.attachmentBehavior];
        } 

    }

}

Hope this helps someone else trying to do the same thing, and if anyone knows the settings for UIAttachmentBehavior to get the same feel as a UIScrollview, could you let me know, thanks