Framework subset

Native class definitions

Framework classes are registered as NativeClassDef records. Each declares a descriptor, a superclass, instance fields, static fields, and method tables. Methods are plain JavaScript functions that receive (self, args, vm).

JAVA_CORE_CLASSES['Ljava/lang/Runtime;'] = nativeDef('Ljava/lang/Runtime;', {
  super: 'Ljava/lang/Object;',
  methods: {
    'availableProcessors()I': () => deviceCapabilities().cores,
  },
});

Views

A View carries geometry (left, top, right, bottom), measured size, layout params, padding, background and children. measure computes desired size from MeasureSpec constraints; layout places children; draw paints to the canvas.

ViewGroup subclasses implement their own measurement strategies:

Class	Strategy
LinearLayout	Orientation, weights, gravity
FrameLayout	Stack children, apply gravity
RelativeLayout	Relative constraints, two-pass resolution
ScrollView	Single scrolling child
CoordinatorLayout	Behavior-driven layout

Layout params

getLayoutParams() resolves the params class from the parent. For framework parents, apk.js looks for a nested class whose descriptor matches <Parent>$X and whose superclass chain reaches ViewGroup$LayoutParams. When nothing matches, it falls back to the parent's declared generateLayoutParams return type.

This keeps params classes coming from the APK's own DEX, so custom LayoutParams subclasses behave correctly.

Resources

Resources wraps the resource table. getText, getColor, getDrawable and getLayout resolve IDs against the table, handling configuration variants and references. Layouts parse through the same AXML reader as the manifest.

Device info

Device identity prefers live browser values over fixed defaults:

const caps = deviceCapabilities();
// { cores, memoryBytes, availBytes, touchPoints }

navigator.hardwareConcurrency, navigator.deviceMemory and navigator.maxTouchPoints feed Runtime, MemoryInfo and ActivityManager. When a browser withholds them, the fallback keeps apps running.

ro.* system properties follow the same rule: navigator.platform and navigator.language shape ro.product.device and ro.product.locale, with browser and en-US as fallbacks.