Now that iOS 8 with the all-new Photos is here, we can see exactly how Extensions work! (I know we haven't even looked at Photos itself yet, but this is a Really Big Deal™ so I want to jump right into Extensions).

Let's get started…

What are Extensions?

Extensions is one of the new capabilities of iOS 8 and PhotoKit. Extensions allow developers to write their app so it “extends” the abilities of other apps and services. You'll find Extensions all over iOS 8, but in this case of course we're focusing on Extensions for the Photos app.

Third party apps can still operate like they always have; as a stand-alone app where you open a photo, edit it, and save it. But if an app is enabled as an Extension, it makes getting in and out of it a lot quicker. Instead of, say, starting and edit in Photos, leaving Photos, opening another app, opening your photo, editing it, saving it, leaving the app, opening another app, opening that saved photo, editing, saving, leaving, repeating, you can simply open your photo in that Extension right from the Photos app, then jump into another app, and so-on.

What apps work as Extensions?

As of this writing, not many, but iOS 8 was only released 48 hours ago. There are undoubtedly thousands of apps in the App Store review process, many of which I'm sure have already been updated for Extensions. The one we'll be using as an example is a curious little app called Fragment - Prismatic Effects By Pixite LLC [$1.99 on the App Store].

How do you know if an app works as an Extension?

If the app is already installed, then just go to Photos and try to add it as an extension (instructions on that in a moment). If it shows up there, it's been updated. If not, it hasn't.

If you don't have the app installed, or want to find out before you buy, check the release notes on the app for something like “Open in Photos app using Extensions”. There doesn't seem to be a specific callout for this function in the app Information list. If you don't see what you're looking for, certainly you can check with the developer, and encourage them to update their apps!

Do apps have to become Extensions?

I don't believe there's any requirement to this, but I could be wrong. Developers could well not bother, but it's a pretty great feature; I can't imagine them not wanting to.

Do Extensions-enabled apps still work on their own?

Absolutely. Apps can still be used stand-alone, and in fact before you can use it as an Extension, you have to enable that feature manually. So yes, every app still works as it always has.

What I don't know is if developers can restrict what functions are available when running in “Extension mode”, for lack of a better term.

How do you enable an Extension?

Easy! First, go to Photos, and open any picture. Tap the Edit button, and then on the Extensions icon, which I guess is really a “more” icon—three dots inside a circle. If this is the first Extension you've enabled, all you'll see is another More button.

The three dots designate “more”… tape that to access the Extensions pane, then tap More again

Tap on the big More button, and you'll get to the Photo Editors window (think of it like an extensions manager). Here you can enable, disable, and rearrange your apps.

This is your list of Photo Editors, where you can choose which you want to see in Photos

Enable one or more, click Done, and you'll see this:

The Fragment app app has now been enabled as an Extension

To edit your photo in an app, of course just tap on the app here, and away you go!

What happens next?

The Extension/app slides into place, and you can edit away, just as you would in the app itself. When you're done, tap Done in the corner (or Cancel if you change your mind).

Fragment is a weird little app… but oddly cool!

You'll be brought back to Photos, with your edits in place.

Continue editing, but…

Here's the really important thing to know. If, right now, you tap on the Extensions/more button again, and open that same app, you should be able to pick up editing as if you'd never left. I say “should” because with many apps I tested, this did not work. The app had “baked in” its changes, so you could no longer edit them. This is not how the API is supposed to work, so this tells me that some developers got lazy and basically added the ability to open your photo in their app as an extension, but didn't bother to save the state so you could pick up where you left off.

HOWEVER…

In many cases it won't much matter. Because at this point if you do anything else to edit the photo — using Photos' own adjustments, or another app — the last app applied will be baked in.

You can however click Done in Photos, returning you to the Photos app, go work on other pictures or anything else, then open up that photo, tap Edit, Extensions and open the app — and you actually will be able to continue editing. Just don't add anything else to it first. As long as you keep that in mind, it is quite cool to be able to come back and edit.

ALSO…

You can always revert. You can go back to where you started, so it's truly non-destructive, however there's no going step-by-step back, or editing “step one” once you've moved on to “step two”.

This is exciting stuff

This certainly makes the process of doing multi-app edits a lot easier. Plus you don't have to save 20 copies of a photo as you go through all the apps. Needless to say it'd be really, really amazing if you could go back and edit each plugin at any time, no matter what else had been done to it, but I'd imagine this is partially a processing power issue, and partially a UI issue. Maybe that ability will come, and certainly if you want to see that, make it known to Apple.

It'll also be interesting to see what happens when Photos comes to OS X. Handoff between iOS devices exist for apps like this — you should be able to start editing in Fragment on your iPad, then pick it up on the iPhone using Handoff. At least, that's what the documentation says, although I couldn't get it to work. I kept getting a “Cannot Open” error. And this only worked (insofar as the Handoff icon showed up on the other device) when working in the app itself, not while working on it as an Extension in Photos. So, limited use there. But if this app comes to OS X and acts as a Photos Extension there, what else will we see?