When you have a well-designed view that responds to gestures and transitions between states, make sure the view runs fast. To avoid a UI that feels sluggish or stutters during playback, make sure animations consistently run at 60 frames per second.
Speed up your view
To speed up your view, eliminate unnecessary code from routines that are called frequently. Start
with
onDraw(),
which gives you the biggest payback. In particular, eliminate allocations in onDraw(),
because allocations might lead to a garbage collection that causes a stutter. Allocate objects
during initialization or between animations. Never make an allocation while an animation is
running.
In addition to making onDraw() leaner, make sure it's called as infrequently as
possible. Most calls to onDraw() are the result of a call to
invalidate(), so eliminate
unnecessary calls to invalidate().
Another very expensive operation is traversing layouts. When a view calls
requestLayout(), the
Android UI system traverses the entire view hierarchy to find how big each view needs to be. If it
finds conflicting measurements, it might traverse the hierarchy multiple times. UI designers
sometimes create deep hierarchies of nested
ViewGroup objects. These deep view
hierarchies cause performance problems, so make your view hierarchies as shallow as possible.
If you have a complex UI, consider writing a custom ViewGroup to perform its layout.
Unlike the built-in views, your custom view can make application-specific assumptions about the size
and shape of its children and therefore avoid traversing its children to calculate measurements.
For example, if you have a custom ViwGroup that doesn't adjust its own size to fit
all its child views, you avoid the overhead of measuring all the child views. This optimization
isn't possible if you use the built-in layouts that cater to a wide range of use-cases.