Question

I have cells in a table with custom fields that allow entry of numbers using a custom numpad. That includes a tab. When tabbing from the bottom of the table to the top, I need to (i) scroll the table to the top and (ii) select the custom field in that table.

I’m finding that if I call cellForRowAtIndexPath directly after I’ve called scrollToRowAtIndexPath, the former returns a null cell. If called again, after the scroll has completed, the cell is returned as expected. I need the cell intself so I can get the custom view by tag value, and select it.

I have been trying to find a solution. One might be to insert a delay after the scroll to allow it to complete. But I’ve tried using performSlector:withObject:afterDelay without success.

This is my code called when the tab is pressed.

-(void) customDualViewTabbed:(CustomDualView *)dualView {

 UITableViewCell *cell=(UITableViewCell*)([dualView superview].superview);
 NSIndexPath *fromIndexPath=[self.tableView indexPathForCell:cell];
 NSIndexPath *toIndexPath;

 if ((fromIndexPath.row+1)<[self.tableView numberOfRowsInSection:fromIndexPath.section]){
  toIndexPath = [NSIndexPath indexPathForRow:(fromIndexPath.row+1) inSection:fromIndexPath.section];
 }
 else {
  toIndexPath = [NSIndexPath indexPathForRow:0 inSection:fromIndexPath.section];
  [[self tableView] scrollToRowAtIndexPath:toIndexPath atScrollPosition:UITableViewScrollPositionTop animated:YES];
 }

 //get cell we tabbed to
 cell=[self.tableView cellForRowAtIndexPath:toIndexPath];

 CustomDualView *dualView2 =(CustomDualView *)[cell viewWithTag:dualView.tag];

 [dualView2  setSelected:(SelectedState)SelectedLeftTabbed];
}

Answer 1

The cells in a UITableView are only loaded as needed. As a result, if the cell that you are scrolling to resides at an index that currently off-screen, you will get a nil response from cellForRowAtIndexPath.

Now, since UITableview conforms to the UIScrollViewDelegate protocol, you can implement those delegate methods in addition to the UITableViewDelegate methods. Implementing one that you know will be called when your cell is in view, like scrollViewDidEndDecelerating:, and then making your call to cellForRowAtIndexPath might do the trick.