CODEWITHSUNDEEP
iphoneuiscrollview
Kamchatka
Kamchatka

Reputation: 3675

Understanding UIScrollView

I'm trying to understand how UIScrollView works for zooming.

I was trying to rotate a UIImageView within a zoomed UIScrollView and I ended up with weird sizes, my centering in the scrollview not working anymore.

I solved the problem by setting the zoomScale to 1.0 before doing the rotation, and then by resetting it back to the previous value once the transformation was done.

I was wondering what was the impact of the UIScrollView on its subviews. Does it change their sizes, their positions. Or is it simply the UIScrollView that handles the zooming and the drawing of the zoomed subviews.

Upvotes: 1

Views: 395

Answers (1)

Scriptable
Scriptable

Reputation: 19750

I realise that is an old question, but I thought I'd add additional information for those still arriving here like myself.

The scroll view manages its contents view, it zooms by adding tranformations to the content. So, for an image when you zoom in, it uses a tranformation to scale the image to the required zoom level.

When you are panning/scrolling a ScrollView, it changes the zoom level and origin positions to move the content around. So the content may well be larger than the scrollview itself. It clips the content at the scrollviews bounds and just adjusts this origin position.

The central notion of a UIScrollView object (or, simply, a scroll view) is that it is a view whose origin is adjustable over the content view. It clips the content to its frame, which generally (but not necessarily) coincides with that of the application’s main window. A scroll view tracks the movements of fingers and adjusts the origin accordingly. The view that is showing its content “through” the scroll view draws that portion of itself based on the new origin, which is pinned to an offset in the content view. The scroll view itself does no drawing except for displaying vertical and horizontal scroll indicators. The scroll view must know the size of the content view so it knows when to stop scrolling; by default, it “bounces” back when scrolling exceeds the bounds of the content.

Source Documentation

Upvotes: 1

Related Questions