Objective C: How can use two scrollview, one inside the another? - iphone

Question

I have two scrollview, one scrollview inside another and I want to scroll my main scrollview content first after that only I want to scroll subview scroll
CGFloat scrollOffset = texscrl.contentOffset.y;
if (scrollOffset == 0)
{
//This condition will be true when scrollview will reach to bottom
self.ArtistScroll.scrollEnabled=YES;
texscrl.scrollEnabled=YES;
}else
{
self.ArtistScroll.scrollEnabled=NO;
texscrl.scrollEnabled=YES;
}
Here, am using content offset for this.. so can anyone help me?

Answer 1

You can achieve the affect you describe by using a third scrollview to actually handle the touch gestures and manually set the contentOffset of the other scrollviews.
Here is how to achieve this for vertically scrolling content, which is I think what you are describing. In the code, outerScrollView is the main scrollview, innerScrollView is the sub-scrollview that is contained by the outer scrollview, and trackingScrollView is the third scrollview that only handles the touches - it has no content.
Create the three scrollviews such that trackingScrollView exactly covers outerScrollView. (I assume you will do this in XIB or storyboard so there is no code.)
Once your scrollviews have content (and whenever their contentSize or bounds change) you should set the contentSize of trackingScrollView:
self.trackingScrollView.contentSize = CGSizeMake(self.trackingScrollView.bounds.size.width,
self.outerScrollView.contentSize.height + self.innerScrollView.contentSize.height - self.innerScrollView.bounds.height);
This makes the content height be that of outerScrollView plus the scrollable distance of innerScrollView, allowing trackingScrollView to scroll over the total travel distance of both scrollviews.
Delegate for trackingScrollView and implement scrollViewDidScroll:
- (void) scrollViewDidScroll:(UIScrollView *)scrollView {
if (scrollView == self.trackingScrollView) {
CGFloat const offsetY = self.trackingScrollView.contentOffset.y;
// Calculate the maximum outer scroll offset
CGFloat const maxOuterOffsetY = self.outerScrollView.contentSize.height - self.outerScrollView.bounds.height;
// Calculate the maximum inner scroll offset
CGFloat const maxInnerOffsetY = self.innerScrollView.contentSize.height - self.innerScrollView.bounds.height;
if (offsetY < maxOuterOffsetY) {
// Scroll is within the outer scroll area or the top bounce zone
self.outerScrollView.contentOffset = CGPointMake(0, offsetY);
self.innerScrollView.contentOffset = CGPointZero;
} else if (offsetY < maxOuterOffsetY + maxInnerOffsetY) {
// Scroll is within the inner scroll area
self.outerScrollView.contentOffset = CGPointMake(0, maxOuterOffsetY);
self.innerScrollView.contentOffset = CGPointMake(0, offsetY - maxOuterOffsetY);
} else {
// Scroll is within the bottom bounce zone
self.outerScrollView.contentOffset = CGPointMake(0, offsetY - maxInnerOffsetY);
self.innerScrollView.contentOffset = CGPointMake(0, maxInnerOffsetY);
}
} else {
// Handle other scrollviews as required
}
}
Effectively we divide the tracking scroll area into two parts. The top part controls the scrolling within the outer scrollview and the bottom part controls the inner scrollview.
Assuming bounce is turned on (which generally it should be) we also need to handle scrolling outside the scroll area. We want the bounce to show on the outer scrollview so the top bounce is handled implicitly by the first conditional. However, the bottom bounce has to be handled explicitly by the third conditional, otherwise we would see the bounce on the inner scrollview.
To be clear, in this solution the two content scrollviews (outerScrollView and innerScrollView) do not receive any touches at all; all input is going to trackingScrollView. If you want input to subviews of the content scrollviews you will need a more advanced solution. I believe this can be done by putting trackingScrollView behind outerScrollView, removing outerScrollView's gesture recognizers and replacing them with those from trackingScrollView. I have seen this technique presented in an old WWDC session on UIScrollView but I have not tried it myself.