Is there a way to trigger an event, such as with 开发者_开发百科an IBAction, when a user scrolls to the bottom of a UITableView? I would like to add more rows if this happens. How do I do this?

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Unless it´s a little late, but i think i found a better solution:

instead of

 - (void)scrollViewDidScroll: (UIScrollView)scroll

i used

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate

This is much more convenient, cause the event is only triggered once. I used this code in my application to load more rows in my tableview at the bottom (maybe you recognize this type of reloading from the facebook application - only difference that they are updating at the top).

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {    
    NSInteger currentOffset = scrollView.contentOffset.y;
    NSInteger maximumOffset = scrollView.contentSize.height - scrollView.frame.size.height;

    if (maximumOffset - currentOffset <= -40) {
        NSLog(@"reload");
    }
}

Hope anyone will help this.

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Simply listen to the scrollViewDidScroll: delegate method, compare the content offset with the current possible offset and if lower then some threshold call your method to update the tableview. Don't forget to call [tableView reloadData] to make sure it reload the newly added data.

EDIT: Put together abstract code, not sure if it works, but should.

- (void)scrollViewDidScroll: (UIScrollView *)scroll {
     // UITableView only moves in one direction, y axis
     CGFloat currentOffset = scroll.contentOffset.y;
     CGFloat maximumOffset = scroll.contentSize.height - scroll.frame.size.height;

     // Change 10.0 to adjust the distance from bottom
     if (maximumOffset - currentOffset <= 10.0) {
          [self methodThatAddsDataAndReloadsTableView];
     }
}

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I use this snippet. in tableView:willDisplayCell:forRowAtIndexPath: I check, if the cell with the last index path is about to be diplayed.

For a tableView with one section:

[indexPath isEqual:[NSIndexPath indexPathForRow:[self tableView:self.tableView numberOfRowsInSection:0]-1 inSection:0]

with more sections:

[indexPath isEqual:[NSIndexPath indexPathForRow:[self tableView:self.tableView numberOfRowsInSection:0]-1 inSection:[self numberOfSectionsInTableView:self.tableView]-1]

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-(void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath
{
    if(!_noMoreDataAvailable)
    {
        if ([indexPath isEqual:[NSIndexPath indexPathForRow:[self tableView:self.tableView numberOfRowsInSection:0]-1 inSection:0]])
        {
            [self.dataSourceController fetchNewData];
        }
    }
}

after fetching the dataSourceController will inform the tableView delegate and this will reload the data.

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NSInteger currentOffset = scrollView.contentOffset.y;
NSInteger maximumOffset = scrollView.contentSize.height - scrollView.frame.size.height;

// Hit Bottom?
if ((currentOffset > 0) && (maximumOffset - currentOffset) <= 10) {
   // Hit Bottom !! 
}

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It can be achieved in much simpler way I guess, you just need to determine the scrolling direction as in this case it is when the user is scrolling downwards.

First in your .h file declare a variable :

CGPoint pointNow;

In .m file, in scrollViewDidScroll method we need to implement this code:-

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    if (scrollView.contentOffset.y > pointNow.y) {
        //Enter code here
    }
}

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Swift

Here is the Swift version of @user944351's answer:

func scrollViewDidEndDragging(scrollView: UIScrollView, willDecelerate decelerate: Bool) {
    
    let currentOffset = scrollView.contentOffset.y
    let maximumOffset = scrollView.contentSize.height - scrollView.frame.size.height
    
    if maximumOffset - currentOffset <= -40 {
        print("reload")
    }
}

Just add this method to your UITableView delegate class. I found -40 too large but you can adjust it according to your needs.

More info

• See my fuller answer that has an example of method to reload data using limits and offsets for the database.

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I'm not sure why you'd want to do this, but I imagine you could add some code to your cellForRowAtIndexPath method so that if indexPath.row == the last row, call the method to add more rows...