Question

I’m trying to implement a twitter iPhone app like interface. (Swipe to replace view in a tableviewcell with a custom view). I’m using Apple’s UISwipeGestureRecognizer to recognize the swipe and I’m getting the start location for that swipe using [recognizer locationInView:self.view]. This gives me a CGPoint and I’m using that with [tableView indexPathForRowAtPoint:location]. My problem with this is, my swipe always seems to get detected at one row above or below the actual row that I swiped in. Has anyone been experiencing the same issue?

EDIT: I should probably also mention that I’m using a custom tableview cell, and it’s height is more than the default view. I’m not sure if that makes any difference, I’m using heightForRowIndexAtPath: to return the height.

My code is –

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
ModelObject *rowData = (ModelObject *)[tempArr objectAtIndex:indexPath.row];
if (rowData.isAlternateView) {
        // Load alternateview
    UISwipeGestureRecognizer *recognizer = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(handleSwipe:)];
    [recognizer setDirection:(UISwipeGestureRecognizerDirectionRight)];
    [cell addGestureRecognizer:recognizer];
    [recognizer release]; 
    return cell;

}
else {
    // Load the correct uitableviewcell
    UISwipeGestureRecognizer *recognizer = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(handleSwipe:)];
    [recognizer setDirection:(UISwipeGestureRecognizerDirectionRight)];
    [cell addGestureRecognizer:recognizer];
    [recognizer release]; 

    return cell;
}

}


-(void) handleSwipe:(UISwipeGestureRecognizer *) recognizer
{
NSLog(@"Swipe detected!");
CGPoint location = [recognizer locationInView:self.view];   
NSIndexPath *selectedIndexPath = [tableView indexPathForRowAtPoint:location];
NSLog(@"Swipe detected at %d", selectedIndexPath.row);
ModelObject *rowData = (ModelObject *)[modelArr objectAtIndex:selectedIndexPath.row];
rowData.isAlternateView = YES;

for (int i=0; i<[tempArr count]; i++) {
    if (i!=selectedIndexPath.row) {
        ModelObject *rowToBeCleared = (ModelObject *) [modelArr objectAtIndex:i];
        if ([rowToBeCleared isAlternateView]) {
            [rowToBeCleared setIsAlternateView:NO];
            [tableView reloadRowsAtIndexPaths:[NSArray arrayWithObjects:[NSIndexPath indexPathForRow:i inSection:0],nil] withRowAnimation:UITableViewRowAnimationLeft];
        }
    }
}

[tableView reloadRowsAtIndexPaths:[NSArray arrayWithObjects:selectedIndexPath,nil] withRowAnimation:UITableViewRowAnimationRight];
}

Answer 1

First, rather than adding a gesture recognizer to each cell, I’d suggest adding just one gesture recognizer to the whole view that contains the table view (or if this is a UITableViewController, then they’re the same thing).

In viewDidLoad:

UISwipeGestureRecognizer *recognizer = [[UISwipeGestureRecognizer alloc] 
    initWithTarget:self action:@selector(handleSwipe:)];
[recognizer setDirection:(UISwipeGestureRecognizerDirectionRight)];
[self.view addGestureRecognizer:recognizer];
[recognizer release];

Then, in the handleSwipe method:

- (void)handleSwipe:(UISwipeGestureRecognizer *) recognizer
{
    //might need to check if swipe has ended (otherwise not time to handle yet)
    if (recognizer.state != UIGestureRecognizerStateEnded)
        return;

    CGPoint location = [recognizer locationInView:tableView]; //not self.view  
    NSIndexPath *selectedIndexPath = [tableView indexPathForRowAtPoint:location];

    if (selectedIndexPath != nil)
    {
        //user swiped on a tableview cell
    }
    else
    {
        //user did not swipe on a tableview cell
    }
}