iOS-处理大图像

Question

I have an iOS app in which I am dealing with variably sized images that are included in links that I download from the web. The images don't need to be stored so I am using EGOImageView which is a UIImageView extension that caches images in the background and these images are in a UITableView. All of this works perfectly for images of below 1000x1000 or so pixels but the bigger pictures are a problem. They download in the background just fine but just setting the cached image as the UIImageViews image takes so much time for the really big images that it makes scrolling through the Table View very choppy when there are many large images.

My question then is what can I do to make it so that simply loading these images into a UIImageView is not a huge burden on the main thread?

Answer 1

I had to do some work around this recently,

My solution was quite simple.

1. Download the image (AFNetworking) and store it in the documents directory
2. Resize the image (Core Graphics) to create a "thumbnail" version for when you are scrolling
3. when the user presses the cell to see the image - show the larger image.

You can use AFNetworking to download the image to the disk and then resize using Core Graphics. I wrapped mine up in an NSOperation and added them to a queue so it didn't freeze up any UI.

The reason you are seeing a laggy response is that those images are getting held in memory which is fine for smaller tables but it isn't scaleable. It could also be because your fetch is being done on the main thread.

Hope this has sent you in the right direction.

https://github.com/AFNetworking/AFNetworking

CoreGraphics Image resize