How does the addSharedElement api that was added to FragmentTransaction work?

Question

Api 21 has added an api called addSharedElement that looks like it is supposed to be used similar to shared views with activity transitions, see: http://developer.android.com/reference/android/app/FragmentTransaction.html#addSharedElement(android.view.View, java.lang.String))

I attempted to use this api by setting android:transitionName on a view in both fragments and then calling addSharedElement on the FragmentTransaction. On the fragment, I called setSharedElementEnterTransition(new ChangeImageTransform());.

However, this has no effect.

I am running this on the Lollipop preview that was released earlier this month.

Answer 1

The api addSharedElement(view, name) will match the View view in the exiting Fragment (it can have any non-null transitionName) with a View in the entering Fragment with the transitionName name. This allows you to have different transitionNames from the leaving Fragment and the entering Fragment.

This is a common use case when you have several Views that can be shared elements in a Fragment. For example, a list of images on your device. When you click on one, it replaces the Fragment with a new one that has a detailed View or single image View. The list will give each image a transitionName unique to the item. This could be the row id or content URI, for example. In the single-image view, the transitionName could be constant. Let's say it is "largeImage." You could match them up easily:

fragmentTransaction.addSharedElement(imageIcon, "largeImage");