why is my function called twice?

I have a swipe recognizer attached to cells in my table view

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];

      //swipe recognition
        UISwipeGestureRecognizer *g = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(cellWasSwiped:)];
        [cell addGestureRecognizer:g];
    开发者_JS百科    [g release];


    }


    // Configure the cell...
    [[cell textLabel] setText:[NSString stringWithFormat:@" number %d", indexPath.row]];
    return cell;
}

and the swipe function is

- (void)cellWasSwiped:(UIGestureRecognizer *)g {
    NSLog(@"sunt in cellWasSwiped");
    swipeViewController *svc = [[swipeViewController alloc]init];
  [self.navigationController pushViewController:svc animated:YES];
  [svc release];
}

and by introducing breakpoints i see that my swipe function is called 2 times and there are two identical view controllers pushed on my navigation controller. Why is my swipe function called twice when i swipe a cell?

Your cellWasSwiped can be called multiple times on change of UIGestureRecognizer state. You need to check property state, it will be UIGestureRecognizerStateEnded when user finished his action. It's also good to check for states UIGestureRecognizerStateFailed and UIGestureRecognizerStateCancelled.

I had that same specific problem with swiping in a table cell. My recognizer method was called twice with state UIGestureRecognizerStateEnded.

I worked around it as follows:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

  static NSString *CellIdentifier = @"CellIdentifier";

  UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
  if (cell == nil) {
    //... create cell
    //... create swipe recognizer (in my case attached to cell's contentView)
  }

  for (UIGestureRecognizer* g in cell.contentView.gestureRecognizers)
    g.enabled = YES;
}

and then

-(void) cellWasSwiped: (UIGestureRecognizer*) recognizer {

  if (recognizer.state != UIGestureRecognizerStateEnded)
    return;

  if (recognizer.enabled == NO)
    return;

  recognizer.enabled = NO;

  //... handle the swipe
  //... update whatever model classes used for keeping track of the cells
  // Let the table refresh
  [theTable reloadData];
}

Instead of adding the gesture recognizer to the cell directly, you can add it to the tableview in viewDidLoad.

In the cellWasSwiped-Method you can determine the affected IndexPath and cell as follows:

-(void)cellWasSwiped:(UIGestureRecognizer *)gestureRecognizer {

  if (gestureRecognizer.state == UIGestureRecognizerStateEnded) {
        CGPoint swipeLocation = [gestureRecognizer locationInView:self.tableView];
        NSIndexPath *swipedIndexPath = [self.tableView indexPathForRowAtPoint:swipeLocation];
        UITableViewCell* swipedCell = [self.tableView cellForRowAtIndexPath:swipedIndexPath];
        // ...
  }
}