You're on the right track placing this inside didSelectRowAtIndexPath:. However, setting user interaction enabled on the textfield just means that the user would be allowed to interact with the object if they tried. You're looking for becomeFirstResponder.
- (void) tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [self.tableView cellForRowAtIndexPath:indexPath];
[cell.textField becomeFirstResponder];
}