1，概述

一直以为调用context.getResources().getDimension(R.dimen.xxx)只会获取dimens.xml

中写入的值，但其实已经转换为屏幕desity对应的像素值了；

2，源码

public float getDimension(@DimenRes int id) throws NotFoundException {final TypedValue value = obtainTempTypedValue();try {final ResourcesImpl impl = mResourcesImpl;impl.getValue(id, value, true);if (value.type == TypedValue.TYPE_DIMENSION) {return TypedValue.complexToDimension(value.data, impl.getDisplayMetrics());}throw new NotFoundException("Resource ID #0x" + Integer.toHexString(id)+ " type #0x" + Integer.toHexString(value.type) + " is not valid");} finally {releaseTempTypedValue(value);}}

跟进complexToDimension,

public static float complexToDimension(int data, DisplayMetrics metrics){return applyDimension((data>>COMPLEX_UNIT_SHIFT)&COMPLEX_UNIT_MASK,complexToFloat(data),metrics);}

继续跟进，可以看到根据unit类型，全部转换成了px值；

public static float applyDimension(int unit, float value,DisplayMetrics metrics){switch (unit) {case COMPLEX_UNIT_PX:return value;case COMPLEX_UNIT_DIP:return value * metrics.density;case COMPLEX_UNIT_SP:return value * metrics.scaledDensity;case COMPLEX_UNIT_PT:return value * metrics.xdpi * (1.0f/72);case COMPLEX_UNIT_IN:return value * metrics.xdpi;case COMPLEX_UNIT_MM:return value * metrics.xdpi * (1.0f/25.4f);}return 0;}