ScrollView as PhotoViewer, load Images only if needed

Question

I would like to create a PhotoViewer for an iPhone.

For that, I already created a ScrollView with Paging enabled in that I add programmically add the UIImageViews. The problem I see is, that if I would have like 100 Images and I would all add to the ScrollView it would take alot of performance and memory.

How would you make it more performant? I thought about loading the Images of the following 2 pages and releasing the Images after the 2 Images before when scrolling through the pages.

I thought about creating a Subclass of UIScrollView and to name it UIPhotoScroller (or something like that). But I also want to show a UIView in the MainWindow with Information about the Images. Is it possible to make the UIView visible from the Subclass?

You really would help me with that. Thank you in advance :D

If the User taps on an image that is in the ScrollView-Subclass, i want to show the UIView with informations which is with the ScrollView-Subclass in the XIB — Kevin Glier, Mar 24 '11 at 20:46

score 1 · Answer 1 · answered Mar 24 '11 at 21:15

Create an NSCache.
When you need a particular image, try to get it from the cache. If it's not there, load it from disk and save it in the cache. The filename is a suitable key.
When you get a memory warning, tell the cache to empty itself.
The cache will release some of its entries periodically, depending on how it's configured. This is a good thing, but you might want to adjust it to have a particular total memory size. Tweak its parameters until it behaves like you want it to. To see your memory usage, use Instruments.

score 0 · Answer 2 · edited May 23 '17 at 12:04

How about doing a UITableView with a single photo per cell. When a cell is being request by the data source, you display a spinner and have a queued NSOperation load the image and refresh the row when done.
You can control the amount of concurrent ops with a NSQueue, so you have complete control on performace/responsiveness. You can then remove old cached images when low on memory/paging, etc.

There are solutions to horizontal UITableView if you need horizontal scrolling.

score 0 · Answer 3 · answered Mar 24 '11 at 20:51

0

Have you looked at the three20 library? There's an example of creating a great Photos app-like viewer of photos, and it's pretty easy to work with the three20 library.

Hope this helps!

answered Mar 24 '11 at 20:51

donkim

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ScrollView as PhotoViewer, load Images only if needed

3 Answers3