UITableView scrollToRowAtIndexPath only scrolls sometimes

Question

I have a UITableView with several UITableViewCells and inside these cells are UITextFields. I implemented a UIToolbar for switching between the different textfields. I can go to the next textfield in the next cell or to the previous textfield. This works fine until a cell should become first responder which is currently not visible in the tableview.

I figured out that

[self.tableview cellForRowAtIndexPath:indexPath]

returns nil and that manually scrolling to the cell with the textfield, which should become first responder, removes the problem. Therefore I tried scrolling to the cell before changing it to become first responder.

I tried that with

[[self.tableView scrollToRowAtIndexPath:newIndexPath atScrollPosition:UITableViewScrollPositionBottom animated:YES];

but unfortunately the tableview does not scroll to this cell but to all other cells. When I add a breakpoint to this line the problem doesn't occur. It also looks like the tableview is scrolling to the cell but then scrolls down again.

Here is the code of cellForRowAtIndexPath:

UITableViewCell *cell;
static NSString *AttributeCellIdentifier = @"AttributeCellIdentifier";
    cell = [tableView dequeueReusableCellWithIdentifier:AttributeCellIdentifier];
    if (cell == nil) {
        [[NSBundle mainBundle] loadNibNamed:@"AttributeCell" owner:self options:nil];
        cell = attributeCell;
        self.attributeCell = nil;
        UITextField * textField = (UITextField *)[cell viewWithTag:1];
        [textField setKeyboardType:UIKeyboardTypeDecimalPad];
        [textField setInputAccessoryView:[self inputAccessoryView]];
    }
UITextField * textField;
textField = (UITextField *)[cell viewWithTag:1];
textField.placeholder = @"C(Probe)/mol/l";
return cell;

Here is the code for switching to the previous textfield:

UIView * currentResponder = [self.view findFirstResonder];

UITextField * newFocusTextField;
UITableViewCell * cell = (UITableViewCell*)[[currentResponder superview] superview];
NSIndexPath* indexPath = [self.tableView indexPathForCell:cell];

newFocusTextField = (UITextField*)[[self.tableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:1 inSection:0]] viewWithTag:1];
[currentResponder resignFirstResponder];
[newFocusTextField becomeFirstResponder];

UITableViewCell * newCell = (UITableViewCell*)[[newFocusTextField superview] superview];
NSIndexPath * newIndexPath = [self.tableView indexPathForCell:newCell];
[self.tableView scrollToRowAtIndexPath:newIndexPath atScrollPosition:UITableViewScrollPositionBottom animated:YES];

Hope this helps.

Please post the code for cellForRowAtIndexPath. Did you write the contents of this method? If so, why is it returning nil? If not, why not? — Rayfleck
I wrote that code and i think it returns nil because the cell is not visible when scrolling doesn't work. From the Documentation for cellForRowAtIndexPath: An object representing a cell of the table or nil if the cell is not visible or indexPath is out of range. — Kai Oelfke
When you tap the toolbar to expose/edit the text field, how does it accomplish that? I'm wondering if there is an ordering problem here, i.e. you might need to scroll the table to expose the cell first, and then make it first responder. — Rayfleck
@Mike - I understand your point and i tried it but this doesn't fix the problem. — Kai Oelfke

lithium lithium · Accepted Answer · 2011-04-26T00:38:52

The code on your post and the problem definition is not hundred percent clear, but there was a bug/glitch in scroll methods' working for iOS 3.0 (i guess specifically 3.0, as far as i remember). I couldnot figure out the reason for it to happen, but it was crashing all the time, although it was OK for iOS 4.x.

The fix was adding a

[table reloadData]

before the scroll line. I know it doesnt make sense, and I know it is not good practice especially if the cell rendering is expensive, but it did solve the problem for that case. I dont know if your problem stems from the same issue, but you may just give it a try...

UITableView scrollToRowAtIndexPath only scrolls sometimes

2 Answers