I am having some trouble understanding the difference between these two Window
flags and am not 100% certain when each needs to be used and why.
The docs for Window.FEATURE_ACTIVITY_TRANSITIONS
say:
Enables Activities to run Activity Transitions either through sending or receiving ActivityOptions bundle created with
makeSceneTransitionAnimation(Activity, Pair[])
ormakeSceneTransitionAnimation(Activity, View, String)
.
And the docs for Window.FEATURE_CONTENT_TRANSITIONS
say:
Flag for requesting that window content changes should be animated using a
TransitionManager
.The
TransitionManager
is set usingsetTransitionManager(TransitionManager)
. If none is set, a defaultTransitionManager
will be used.
The documentation states that the following Window
methods require the FEATURE_ACTIVITY_TRANSITIONS
flag to be enabled, but say nothing about whether or not the FEATURE_CONTENT_TRANSITIONS
needs to be enabled as well (note that according to the source code, FEATURE_ACTIVITY_TRANSITIONS
is true
and FEATURE_CONTENT_TRANSITIONS
is false
for material-themed applications by default):
get{Enter,Exit,Return,Reenter}Transition()
set{Enter,Exit,Return,Reenter}Transition()
getSharedElement{Enter,Exit,Return,Reenter}Transition()
setSharedElement{Enter,Exit,Return,Reenter}Transition()
getTransitionBackgroundFadeDuration()
setTransitionBackgroundFadeDuration()
In other words, it seems like based on this information FEATURE_ACTIVITY_TRANSITIONS
is the feature flag that applications will need to enable in order to use Lollipop's new Activity Transition APIs. What confuses me, however, is that this article from the Android Developers site states that enabling the FEATURE_CONTENT_TRANSITIONS
is required in order to implement custom activity transitions.
So here are my questions:
- What is the difference between these two flags? What is the difference between an "activity transition" and a "content transition" in this context?
- Why is
FEATURE_ACTIVITY_TRANSITIONS
enabled andFEATURE_CONTENT_TRANSITIONS
disabled by default? When is enabling theFEATURE_CONTENT_TRANSITIONS
flag actually required? - Would it ever make sense to sense to disable
FEATURE_ACTIVITY_TRANSITIONS
and enableFEATURE_CONTENT_TRANSITIONS
? Or doesFEATURE_CONTENT_TRANSITIONS
requireFEATURE_ACTIVITY_TRANSITIONS
to be enabled as well?
Thanks!
I'm glad I have an opportunity to answer these questions as the documentation is less than clear.
Early-on, there was one flag
FEATURE_CONTENT_TRANSITIONS
that handled both of the features. We split them when Material applications got unexpected behavior when it was enabled. So some older documentation may still say that you have to enableFEATURE_CONTENT_TRANSITIONS
to get activity transitions when they meanFEATURE_ACTIVITY_TRANSITIONS
.An activity transition in this context means that you call
startActivity
with a bundle created fromActivityOptions.makeSceneTransitionAnimation
or, your activity was started with that bundle. Activity Transitions modify your layout (e.g. fading in elements, moving shared elements), so if your activity doesn't like that, you should disableFEATURE_ACTIVITY_TRANSITIONS
.Content transitions use a
TransitionManager
when you callsetContentView
(other than the first time). Typically, you'll get a cross-fade, but if your Activity's content has things in common, such as sharing IDs or usingtransitionName
, you'll getChangeBounds
behavior between those Views. You can change the details of your transitions by customizing theTransitionManager
associated with your Window either using XML or code.FEATURE_CONTENT_TRANSITIONS
uses a TransitionManager when your content changes. By default, this is a cross-fade and that was very bad for some applications. On the other hand,FEATURE_ACTIVITY_TRANSITIONS
doesn't do anything to most applications by default. You have to opt into starting an activity that way, so it is safe to turn on.Yes, but it is unlikely. If your application likes
FEATURE_CONTENT_TRANSITIONS
, it should work well withFEATURE_ACTIVITY_TRANSITIONS
. If you want to explicitly limit people from calling your activity with shared elements or you don't like the standard enter transition effect, you can disable it to prevent the effect when another applications calls into yours.