CODEWITHSUNDEEP
iosobjective-cuitableview
DevC
DevC

Reputation: 7022

Detect when second tableview cell comes into view - then perform an action

I've got a UITableView in a UIViewController, as well as a filter button. I hide the filter button when the user starts to scroll down the list. I want to then show the filter button when the second cell (index 1) is visible. However, I can't get this desired effect, I can only get it to appear when it reaches the top. Here is my code for when it reaches the top (I then show the filter button again).

//determines when the tableview was scrolled
-(void) scrollViewDidScroll:(UIScrollView *)scrollView
{
    CGPoint currentOffset = scrollView.contentOffset;
     //tableview is scrolled down
    if (currentOffset.y > self.lastContentOffset.y)
      {

    //if the showFilter button is visible i.e alpha is greater than 0
        if (self.showFilter.alpha==1.0) {

            [UIView animateWithDuration:1 animations:^{

                //hide show filter button
                self.showFilter.alpha=0.0;
                //I also adjust the frames of a tableview here
            }];

        }


    }


    //determines if it is scrolled back to the top
    if (self.showFilter.alpha==0.0 && currentOffset.y==0) {
        [UIView animateWithDuration:0.3 animations:^{
            //show filter button
            self.showFilter.alpha=1.0;

          //i also adjust the frames of the tableview here
        }];
    }

    self.lastContentOffset = currentOffset;
}

I have also tried:

if (self.showFilter.alpha==0.0 && currentOffset.y<160)

But it doesn't work to the desired effect as the tableview jumps off the screen. Is there another way to get this desired effect?

Upvotes: 1

Views: 1365

Answers (1)

ndmeiri
ndmeiri

Reputation: 5029

A previous answer suggested that you should check if the cell is visible every time the table view scrolls (in scrollViewDidScroll:). However, you should not do this. That approach could affect the performance of your table view since a check must be performed every single time the table view scrolls.

Instead, you only need to check every time a new cell will become visible by implementing this UITableViewDelegate method:

- (void)tableView:(nonnull UITableView *)tableView willDisplayCell:(nonnull UITableViewCell *)cell forRowAtIndexPath:(nonnull NSIndexPath *)indexPath
{
    if ([indexPath isEqual:[NSIndexPath indexPathForRow:1 inSection:0]]) {
        // perform action
    }
}

Prior to Swift 3 you would write the following:

func tableView(tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {
    if indexPath == NSIndexPath(forRow: 1, inSection: 0) {
        // perform action
    }
}

In Swift 3 or greater you would write the following:

func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
    if indexPath == IndexPath(row: 1, section: 0) {
        // perform action
    }
}

In either case don't forget to set your UIViewController subclass as the delegate of the UITableView.

Upvotes: 3

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