Creating an Image Out of the iOS Surface and Saving It

Creating an image out of the ios surface and saving it

I remember I saw something on this subject (taking screenshots in the background) some time ago. I wasn't able find exact place and code which I saw. The only note which I left for myself was usage of createScreenIOSurface

I googled a little bit and found couple of mentions:

Get a screenshot while App is in background? (Private APIs allowed)

https://github.com/rpetrich/FastBlurredNotificationCenter/blob/master/Tweak.x

http://pastie.org/pastes/3734430

As I remember the code was way more compact then what you showed.

is AVAssetImageGenerator completion handler called in main thread?

IIRC, yes. But you can test it, and to be safe you can wrap your code in a block which dispatches it to the main thread.

Generally speaking, the callback has to return to the main thread as the thread it's started from can't be guaranteed to be running a run loop if it isn't the main thread.

Unless you're scheduling the block you're creating in relation to other operations (dependencies) then I'm not sure what advantage the block gives you as the image loading is asynchronous so you can trigger it from the main thread without blocking anything.

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From your comment, in that case you should switch your code around. Create the block operation inside the completion block which provides you with the image. Add each block operation to your queue. The block operation just takes the image and saves it to disk.

Storing images in Core Data or as file?

There are two main options:

1. Store the file on disk, and then store the path to the image in core data
2. Store the binary data of the image in core data

I personally prefer the 1st option, since it allows me to choose when I want to load the actual image in memory. It also means that I don't have to remember what format the raw data is in; I can just use the path to alloc/init a new UIImage object.

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