Develop Reference

How to include an unattached View in the activity transition?

I draw a View that is not attached to any parent.
It's a decoration for a RecyclerView. The view sticks to the bottom and disappears when its counter part comes up in the list.
All this works fine but:
When i leave the activity the View doesn't fade with the rest of the
views in the activity's transition.
It stays until the end of the animation and then disappears
immediately.
( see large green view in the demo )
How do i include this unattached View in the activity's exit transition?
I've create a minimal Android Studio Project to replicate the issue:
https://github.com/Ostkontentitan/transition-issue-demo
(To better see the issue possibly set your phones animation scale to >= 5)
Here is a demo:

Add transitionName to xml layout for the RecyclerView.
The transition animation you see is because of ActivityOptions.makeSceneTransitionAnimation(this#ItemListActivity) and if you add transitionName to the view, it works fine.

Not-too-educated guess
(because I haven't tried and I haven't used Transition Framework in a few months)
The way TF (Transition Framework) works is by computing the start/end values of the transition and performing the animations needed to achieve this.
RecyclerView decorations are not "views" that are part of the layout, so TF has no idea that thing exists. It does know about your RecyclerView of course, because it's contained in the ViewGroup that is animated.
You may have already know this, but in any case, what I think I'd try to do here, is create a custom transition framework transition (they are not hard to do, you can even check TransitionEverywhere and look at how that library implements some missing transitions in the framework); in your CustomTransition, you can then try to interpolate the animation values so the recycler view can redecorate as the animation progresses (like an alpha value that is animated, your custom decorator would "paint" using said alpha).
Now... in truth, I've had to do something similar once, where a custom transition was "driving" a few external views (for reasons at the time) :) but... it was not a RecyclerView item decoration, mine were just "views", so I'm not sure if you can do this this way w/a decoration.
I think it's worth trying.

Shared Element Transitions Between Views (not Activities or Fragments)

Let's say I'm using a view-based approach to develop an Android application like for example described in the following article: http://corner.squareup.com/2014/10/advocating-against-android-fragments.html
So now I have two full screen views. One is visible and contains a grid of images. The other is hidden and is a detail view of the to-be-clicked image. Without transitions on clicking an image in the grid the grid view will be hidden and the detail view will be shown. Now what if I want to have something akin to a shared element transition between the small image in the grid view and the larger image in the detail view. Is something like this possible?

Yes, transitions allow this.
In your example, you have both the grid and detail views already in your hierarchy. To use transitions, it will work better if the detail view does not start in the View hierarchy. You need to exchange the two views.
There are two (similar) ways to do it. The first is to have the grid view in a scene. Then use TransitionManager.go(detailScene, transition).
The second way is to use TransitionManager.beginDelayedTransition and then swap the detailed layout for the grid layout.
It is important to have the shared views have something in common. Typically it is a View ID or transitionName. This linking will tell the transition system that even though the views are different instances.
The transition that you'll want to use is #android:transition/move. It combines ChangBounds, ChangeTransform, ChangeImageTransform, and ChangeClipBounds. You'll have to target this at the shared element views. It looks like you will need another transition (Fade?) for the entering and /or exiting views.
Something like this:
TransitionSet shared = ...
shared.addTarget("sharedName");
gridElement.setTransitionName("sharedName");
Fade fade = new Fade();
fade.excludeTarget("sharedName", true);
TransitionSet set = new TransitionSet();
set.addTransition(shared)
.addTransition(fade);
TransitionManager.go(detailScene, set);

Android view animation: replacing view by itself

In my android app, I have a notion of "trails": a sequence of objects that the user can navigate. The same view, naturally, is used to display all objects, just updating components (texts, images, etc.) when the next object is to be shown.
Now, I want to animate the transition between objects: when the user navigates from an object to the next object, I want to use the slide animation from right to left (and the other way around). The issue is that I don't have two views to animate between - only one view. Therefore when I try to animate displaying this view (when the next object is to be loaded), the visible view disappears, I get a blank screen - and then the view slides in from the right.
What I want instead is to have the existing view to slide out and be replaced by a new view (same View but with different content) to slide in from the right.
How should I go about it?

Looks to me like a combination of LayoutTransition and GestureDetector. You might even a ViewFlipper in there too.
The LayoutTransition has an animation feature you might want to look into.

I haven't been able to figure out how to use LayoutTransition in my case, so instead of having my View, I replaced it with ViewFlipper containing two copies of my View. When I need to replace the view with another, I keep track of which of the two is currently displayed, then update the other off-screen and then use standard "slide-from-left" and "slide-from-right" animation with showNext(). This is more complicated than I really wanted it to be and uses more memory, but it does the job.

The solution turned out to be very simple: ViewPager. I provide PageAdapter, which returns two similar views (same layout, different content) and ViewPager takes care of the rest. If I wanted to disable the swipe page changes, all I had to do is extend ViewPager, override onInterseptTouchListener and return false.

Animate part of Activity Launch

Is it possible to animate part of an activity launch?
I am not wanting my action bar to animate, however the rest of the view should slide in.
I have tried using a Gallery for this, however I have not been able to animate the gallery while programatically setting the selected view. This is because the gallery does not load more than the currently displayed view and its immediate adjacent views.

When you can use the viewflipper for this. Which shows 1 child at a time. You can set a IN and OUT animation for the views. So when you set the activew view index animations will be applied.

How to draw custom animation as Activity background

I have a standard Activity with its layout, and I have a custom animated View.
I want this View to permorm a fancy "intro" animation, after which the standard Activity is displayed with the animated View as a background.
The application should be compatible with froyo (2.2) devices.

You can use a frame layout and insert two views, one is your custom view animation and the second one which will come on top would be your normal layout.