Iphone – How does UIScrollView steal touches from its subviews

cocoa-touchiphoneuiscrollview

I'd like to be able to create my own container subclasses of UIView which can react first to touches, before their subviews. This is tricky because normally a subview receives touch events (via touchesBegan: etc) before superviews. How does UIScrollView reverse this?

To be clear, I am not asking how UIScrollView behaves. I understand what it does, and how you would normally use it. I'm asking about how I could cleanly implement my own version of this — not because I want to, but because I'm trying to build reusable container views that take advantage of similar behavior.

Best Answer

You can implement hitTest:withEvent: method in your UIView subclass.

This method gets called to check what subview must receive the touch event, so you can perform some action there before it actually happens. You can also change subview that must receive event.

Related Solutions

Iphone – UIScrollview subviews outside of clipping bounds not receiving touches

This may work:

- (UIView*)hitTest:(CGPoint)point withEvent:(UIEvent*)event {
    UIView* child = nil;
    if ((child = [super hitTest:point withEvent:event]) == self)
        return self.scrollView;         
    return child;
}

But if subview is out of scrollview bounds events were not fired and this function returns self.scrollView.

Iphone – How to steal touches from UIScrollView

Sometimes you have to ask the question before you can find the answer. Dan Ray had a similar problem and solved it with a very different solution.

- (UIView*)hitTest:(CGPoint)point withEvent:(UIEvent *)event
{
    UIView* result = [super hitTest:point withEvent:event];

    if ([result.superview isKindOfClass:[UIPickerView class]])
    {
        self.scrollEnabled = NO;
    }
    else 
    {
        self.scrollEnabled = YES;    
    }
    return result;
}

I've tested the code and it works fine for me as well. However, this is not really stealing touches from the scroll view, so if anyone knows how to actually steal touches that would be great.

Source: UIPickerView inside UITableView.tableFooterView doesn't receive drag touches

Best Answer

Related Solutions

Iphone – UIScrollview subviews outside of clipping bounds not receiving touches

Iphone – How to steal touches from UIScrollView

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