Android™ Application Development - Bahar Ali Khan

Chapter 11: Advanced Android Development
Android includes several predefi ned themes as part of the base package, including:
❑ Theme.Black Features a black background with white foreground controls and text.
❑ Theme.Light Features a white background with dark borders and text.
❑ Theme.Translucent Features a partially transparent Form.
You can set the theme of an Activity at run time, but it’s generally not recommended, as Android uses
your Activity’s theme for intra-Activity animations, which happens before your application is loaded. If
you do apply a theme programmatically, be sure to do so before you lay out the Activity as shown in the
code snippet below:
protected void onCreate(Bundle icicle) {
super.onCreate(icicle);
setTheme(android.R.style.Theme_Translucent);
setContentView(R.layout.main);
}
If you don’t apply a theme to your application or any of its Activities, it will use the default theme
android.R.style.Theme.
Advanced Canvas Drawing
You were introduced to the Canvas class in Chapter 4, where you learned how to create your own
Views. The Canvas was also used in Chapter 7 to annotate Overlays for MapViews.
The concept of the Canvas is a common metaphor used in graphics programming and generally consists
of three basic drawing components:
❑ Canvas Supplies the draw methods that paint drawing primitives onto the underlying bitmap.
❑ Paint Also referred to as a “brush,” Paint lets you specify how a primitive is drawn on the
bitmap.
❑ Bitmap Is the surface being drawn on.
Most of the advanced techniques described in this chapter involve variations and modifi cations to the
Paint object that let you add depth and texture to otherwise fl at raster drawings.
The Android drawing API supports translucency, gradient fi lls, rounded rectangles, and anti-aliasing.
Unfortunately, owing to resource limitations, it does not yet support vector graphics; instead, it uses
traditional raster-style repaints.
The result of this raster approach is improved effi ciency, but changing a Paint object will not affect
primitives that have already been drawn; it will only affect new elements.
If you’ve got a Windows development background, the two-dimensional (2D) drawing capabilities of
Android are roughly equivalent to those available in GDI+.
373