Android™ Application Development - Bahar Ali Khan

Chapter 11: Advanced Android Development
❑ Consider Size and Orientation When you’re designing your Views and Overlays, be sure to
consider (and test!) how they will look at different resolutions and sizes.
❑ Create Static Objects Once Object creation in Android is particularly expensive. Where possible,
create drawing objects like Paint objects, Paths, and Shaders once, rather than recreating
them each time the View is invalidated.
❑ Remember onDraw Is Expensive Performing the onDraw method is an expensive process
that forces Android to perform several image composition and bitmap construction operations.
Many of the following points suggest ways to modify the appearance of your Canvas without
having to redraw it:
❑ Use Canvas Transforms Use canvas transforms like rotate and translate to simplify
complex relational positioning of elements on your canvas. For example, rather
than positioning and rotating each text element around a clock face, simply rotate the
canvas 22.5 degrees, and draw the text in the same place.
❑ Use Animations Consider using Animations to perform pre-set transformations of
your View rather than manually redrawing it. Scale, rotation, and translation Animations
can be performed on any View within an Activity and provide a resource-effi cient
way to provide zoom, rotate, or shake effects.
❑ Consider Using Bitmaps and 9 Patches If your Views feature static backgrounds, you
should consider using a Drawable like a bitmap or scalable 9 patch rather than manually
drawing it.
Advanced Compass Face Example
Early in Chapter 4, you created a simple compass. In the last chapter, you returned to it, extending it to
display the pitch and roll using the accelerometer hardware.
The UI of the View used in those examples was kept simple to keep the code in those chapters as clear
as possible.
In the following example, you’ll make some signifi cant changes to the CompassView’s onDraw method
to change it from a simple, fl at compass into a dynamic artifi cial horizon, as shown in Figure 11-2.
Figure 11-2
381