UITableView contentSize and origin - ios

Question

I am just playing around with UITableView and I created 2 buttons.
One of the buttons will cause the table view to scroll up by an amount
while the other will cause the table view to scroll down by an amount.
Scroll up:
[self.tableView setContentOffset:CGPointMake(self.tableView.contentOffset.x, self.tableView.contentOffset.y + up) animated:YES];
up += 10;
Scroll down:
[self.tableView setContentOffset:CGPointMake(self.tableView.contentOffset.x, self.tableView.contentOffset.y + down) animated:YES];
down -= 10;
All is well and fun. But the problem is I don't know how to prevent the scroll from scrolling off screen both on top and the bottom. So far, it will keep scrolling upward or downward even showing white space, the same goes for the bottom.
I have tried using the contentSize property but it doesn't seem to work.
By not working, it means:
if(up < self.tableView.contentSize.height)
{
[self.tableView setContentOffset:CGPointMake(self.tableView.contentOffset.x, self.tableView.contentOffset.y + up) animated:YES];
up += 10;
}
The above is an attempt to disallow scrolling downward when the amount (up) is greater than the contentSize. But it doesn't seem to work.
Is there anyway I could detect the scrolling is off screen both on top and bottom? Other words, I would like to prevent it from scrolling above the first cell and for the bottom past the last cell.

Answer 1

Instead of keeping variables up and down in your class, and shifting the existing contentOffset by those amounts (which you then change, this doesn't make sense to me), why not keep it all local and shift by a constant amount:
- (void)buttonClicked:(id)sender
{
CGPoint offset = self.tableView.contentOffset;
CGSize visibleSize = self.tableView.bounds.size;
if (sender == btnUp)
{
offset = CGPointMake(offset.x, offset.y + 10);
if (offset.y < (self.tableView.contentSize.height - visibleSize.height))
[self.tableView setContentOffset: offset animated:YES];
}
else if (sender == btnDown) { /* you get the idea */ }
}
That part's just an idea...the real solution I think lies in including tableView.bounds in the "should I scroll" check.