detect when uiscrollview frame touch the main screen bounds

how can i detect when a UIScrollViewframe intersect with the main screen (when scrolling) in both direction up and down? i was trying to do it like so :

- (void)detectScreenB开发者_Python百科oundsIntersect{
    if (CGRectIntersectsRect([myScrollView frame], [[UIScreen mainScreen] bounds])) {
        NSLog(@"COLLISION");
    }
} 

But this doesn't seem to work! Thanks.

Adopt the UIScrollViewDelegate protocol in the view controller and set the scroll view's delegate to the controller. Adopt the scrollViewDidScroll: method.

- (void) scrollViewDidScroll:(UIScrollView *)scrollView {
    if ( [self hasReachedAVerticalEdge] ) {
        NSLog(@"At World's End");
    }
}

- (BOOL) hasReachedAVerticalEdge {
    CGPoint offset = myScrollView.contentOffSet;
    CGSize contentSize = myScrollView.contentSize;
    CGFloat height = myScrollView.frame.size.height;
    CGFloat width  = myScrollView.frame.size.width;

    if ( offset.y == 0 || 
         (offset.y + height) == contentSize.height ) {
        return YES;
    }

    return NO;
}

Is this what you are looking for?

Checking if an image view falls in the visible portion of the scroll view.

- (BOOL)isContentFrameVisible:(CGRect)aFrame {
    CGRect visibleRect = CGRectZero;
    visibleRect.origin = myScrollView.offset;
    visibleRect.size = myScrollView.frame.size;

    if ( CGRectIntersectsRect(visibleRect, aFrame) ) {
        return YES;
    }
}