在tableview滚动时拦截UITableView中的TouchUpInside事件

Question

I'm building out a UITableView that has a button in the tableview's section header, so that as the user scrolls down the screen, the button is pinned to the top of the screen.

The problem is that the touch events for the section header's button don't register when the UITableView is moving . The button only gets the touch event if the tableview is not scrolling.

-(UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section
{
    if (!_sectionHeaderView) {
        _sectionHeaderView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, 200)];

        UIButton *backButton = [UIButton buttonWithType:UIButtonTypeCustom];
        backButton.frame = CGRectMake(0, 0, 50, 50);
        [backButton setImage:[UIImage imageNamed:@"upArrow"] forState:UIControlStateNormal];
        [backButton addTarget:self action:@selector(scrollToTop:) forControlEvents:UIControlEventTouchUpInside];
        [_sectionHeaderView addSubview:backButton];

    }
    return _sectionHeaderView;
}

Currently, what happens is: - If the tableview is not scrolling, the button performs as you'd expect: tap it, and the button gets the TouchUpInside gesture. - If the tableview is scrolling, the button doesn't get the TouchUpInside gesture - instead, the tableview just stops in place.

I've tried subclassing the UITableView and looking at the touchesBegan: methods, etc and that didn't work. I see the same pattern: the gestures only show up if/when the tableview isn't moving.

Update: This isn't a usability issue - while I can't show screenshots of the design I'm working on, it's a valid use case to use buttons & controls in the section header.

Here's a quick sketch to explain why:

Answer 1

Figured it out! All you need to do is subclass UITableView , and override hitTest:withEvent:

- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event
{
    if ([[super hitTest:point withEvent:event] isKindOfClass:[UIButton class]]) {
        UIButton *buttonThatWasTapped = (UIButton *)[super hitTest:point withEvent:event];
        [buttonThatWasTapped sendActionsForControlEvents:UIControlEventTouchUpInside];
    }
        return [super hitTest:point withEvent:event];
}

Here's what this code does: if the tableview is touched, and the touch occurred in the bounds of a UIButton, the tableview will forward the touch event to the UIButton.

There's a caveat here: the touch event may get sent to the UIButton several times (I'm seeing the call being made 3 times for each touch). This code was sufficient for my needs, but if you're using this code in your app, watch out for that issue - you may have to modify the above code to account for this.

Answer 2

This is what's supposed to happen.

The user is used to this behavior - it allows them to stop the table view's scrolling when they see what they wanted to touch.

Imagine I was scrolling through a table looking for the row 'unicorns', and I was scrolling really fast (because it's a big table, and I'm not sure where unicorns is). When 'unicorns' crosses my vision, I will instinctively stop the table to select it.

With the current system, I can tap anywhere on the table view and it will stop. If table views were implemented your way, I would tap 'underground rockchucks' to stop the table, and all of a sudden I am looking at information about rockchucks - and I want information about Unicorns.

I now become a disgruntled user, return your app to Apple, and get my $0.99 back.

You don't want users doing that.