Question

I have a UISCrollview. Inside this scroller I have a picture and over the picture I have some objects (as subviews of the picture), like layers in a Photoshop composition. So, if I zoom the picture, the objects will zoom. If I scroll the picture, the objects scroll.

Now consider this: I have the picture zoomed in. The picture is now larger than the iPad screen. I am seeing the top half of the picture. I touch an object that is over the picture and start dragging it to the bottom of the screen. My intent is to drop the dragged object at the bottom of the picture, but as the picture is zoomed in, I have to drag the element to bottom of the screen, release it, scroll the picture up and then continue dragging the object.

What I want is this: I start dragging and when I arrive at the boundary of the screen, the scroller starts scrolling automatically showing parts of the image that were down or up.

What do I need is to know the rect that is visible, a kind of inverse of scrollRectToVisible…

Considering that the picture can be zoomed at any level, how do I know if the element I am dragging is near the border. BTW, how do I know what part of the scroller is being shown, even if it is zoomed?

thanks.

Answer 1

The visible rectangle has a size of scrollView.bounds.size and an origin of scrollView.contentOffset, in the coordinate space of the scrollview. Depending on what exactly you are doing, you may need to use convertRect:fromView: or convertRect:toView: to convert it into the coordinate space of the zoomed view.