Detecting UITableView scrolling

Question

I've subclassed UITableView (as KRTableView) and implemented the four touch-based methods (touchesBegan, touchesEnded, touchesMoved, and touchesCancelled) so that I can detect when a touch-based event is being handled on a UITableView. Essentially what I need to detect is when the UITableView is scrolling up or down.

However, subclassing UITableView and creating the above methods only detects when scrolling or finger movement is occuring within a UITableViewCell, not on the entire UITableView.

As soon as my finger is moved onto the next cell, the touch events don't do anything.

This is how I'm subclassing UITableView:

#import "KRTableView.h"


@implementation KRTableView

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    [super touchesBegan:touches withEvent:event];   
    NSLog(@"touches began...");
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    [super touchesMoved:touches withEvent:event];
  NSLog(@"touchesMoved occured");   
}

- (void)touchesCancelled:(NSSet*)touches withEvent:(UIEvent *)event {
    [super touchesCancelled:touches withEvent:event];
  NSLog(@"touchesCancelled occured");   
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
  [super touchesEnded:touches withEvent:event];
  NSLog(@"A tap was detected on KRTableView");
}

@end

How can I detect when the UITableView is scrolling up or down?

Answer 1

You don't need to intercept the event methods. Check the docs for the UIScrollViewDelegate protocol, and implement the -scrollViewDidScroll: or -scrollViewWillBeginDragging: methods as appropriate to your situation.

Answer 2

I would like to add the following:

If you are working with a UITableView it is likely that you are already implementing the UITableViewDelegate to fill the table with data.

The protocol UITableViewDelegate conforms to UIScrollViewDelegate, so all you need to do is to implement the methods -scrollViewWillBeginDragging and -scrollViewDidScroll directly in your UITableViewDelegate implementation and they will be called automatically if the implementation class is set as delegate to your UITableView.

If you also want to intercept clicks in your table and not only dragging and scrolling, you can extend and implement your own UITableViewCell and use the touchesBegan: methods in there. By combining these two methods you should be able to do most of the things you need when the user interacts with the UITableView.

Answer 3

It was my mistake, I tried to call the method before reloading the tableview. The following code helped me solve this issue.

[mytableview reloadData];

[mytableView scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:btn.tag-1] atScrollPosition:UITableViewScrollPositionTop animated:YES];