How to use DEBUG flags in AOSP classes?

Question

Sometimes in AOSP sources I see private static final boolean debug flag with false as ïts value. And there are debug output if this flag is true. Something like this:

private static final boolean DEBUG_DRAW = false;
private static final Paint DEBUG_DRAW_PAINT;
static {
    DEBUG_DRAW_PAINT = DEBUG_DRAW ? new Paint() : null;
    if (DEBUG_DRAW_PAINT != null) {
        DEBUG_DRAW_PAINT.setAntiAlias(true);
        DEBUG_DRAW_PAINT.setColor(Color.MAGENTA);
    }
}

Who and how uses it? Is it possible to switch this flag somehow and take debug output of AOSP classes?

score 0 · Answer 1 · answered Jun 28 '17 at 12:39

Everything is possible with Java and Reflection

Pros:

I don't think there is anything more powerfull than that

Cons:

This technique will be executed at runtime so any code executed before this (e.g. classes loading)... well, is already executed. So you won't see the effects
Slow at runtime
Dangerous. Use it carefully

You can modify any value using this:

Class<?> klass = ...
Field field = klass.getDeclaredField("DEBUG_DRAW");
field.setAccesible(true);
field.set(
    null, // as this is an static attribute we don't need anything here...
    true  // set true as new value
);

As I stated before reflection is a dangerous technique so that snipped will throw several exceptions if used wrong so you will have to handle them

How to use DEBUG flags in AOSP classes?

1 Answers1