The back button is now contextual, it appears in apps, but disappears when it can't do anything.

What about when an activity in app A opens an activity in app B? Can I still go back to app A's activity from app B's activity?

I just tested this (I think):

I opened a link from fb messenger in chrome. The back button is still there, and clicking it returned me to messenger. So yes I believe so.

That might not be a bad thing. I've used Android for a while, but I'm not always clear if/when the back button will do in-app navigation vs. return me to the phone's home screen.

I've always regarded the back button as a completely random thing.

I've always regarded the back button as the single most important reason why I prefer Android to iOS. Interesting how different people perceive the world.

I agree. The back button in Android almost always seems to do what I would expect. I'm not an iOS user so my perspective probably doesn't mean a lot, but the occasional times I try to use someone else's iOS phone I have no idea what's going on. Nothing seems intuitive.

iOS's Swipe From Left works differently than Android's (at least 8.1 Oreo's) does, but often accomplishes the same task. It's pretty equivalent to Android's back button in a lot of cases, acting as hierarchical navigation and back to previous screen when applicable. The difference is that it only works within an app, which means it won't kick you back to a previous app (unless it's opened in a web view) and won't take you back to the home screen. I typically found iOS to handle it more elegantly than my <=Android8.1 phone, but I haven't updated to Pie yet to see how it's different.

I never said I didn't like it.

The random way the back button works -- moving to iOS I didn't miss it. There are plenty of ways to switch apps, or go back within an app.

I thought I'd miss it. I didn't. Now I wouldn't need it on Android.

If one app activates another (camera -> album -> photo editor -> share), how do you go back from mid-way if you decided to?

Because Android features this metaphor, it's used extensively. Because iOS doesn't, it isn't as much. iOS features different metaphors which achieve the same outcomes in different ways, such as pop-up sheets for the camera, album views and share panes.

And in cases where one app does activate another, you can go back one step by tapping the top-left corner of the screen. There's only one level of "app back", but that's plenty since iOS doesn't tend to jump you between apps a lot, and because that navigation isn't co-mingled with other "back" operations.

There is a link at the top left of the screen that goes back to the previous app during these "app activates another another" phases.

I don't work on Android but isn't that behavior defined by the Android OS and just apps doing whatever they want?

In the event you don't like the new gesture based navigation system you can always revert back to the traditional Back, Home, and Recents layout in settings.

It's now an application navigation function and not an OS navigation function. So in screenshots demonstrating core OS functions it's absent but in screenshots demonstrating Apps it's present.

What are you talking about? I'm using P preview and it's still there. It's also still there in several screenshots at https://www.android.com/versions/pie-9-0/. It's just now hidden when it wouldn't do anything.

I haven't been following P development very closely. It looks like they added it back in Beta 3.

https://news.softpedia.com/news/android-p-beta-3-returns-the...

It's not gone in all of the screenshots the home, back, and menu button are all still there. I think swiping up is just going to be an additional feature to reach the new recents+home row screen.

Running it on my Pixel 2XL, the new navigation pill is strictly optional.

Nope, it's just hidden on the home screen where you're already as far "back" as you can go.

The back button shows up when you open an app.

Probably the same way it works on iPhone, where developers incorporate navigation into the apps.

Until apps adapt what is one supposed to do?

Nothing. It's still there. It's just hidden when it wouldn't do anything.

I can see the back button in two of the screenshots.

The back button is not gone. Yet.