DrawerArrowDrawable

/** A drawable that rotates between a drawer icon and a back arrow based on parameter. */ public class DrawerArrowDrawable extends Drawable { /** * Joins two {@link Path}s as if they were one where the first 50% of the path is {@code * PathFirst} and the second 50% of the path is {@code pathSecond}. * 合并两个路径，前50%为路径1，后50%为路径2 */ private static class JoinedPath { private final PathMeasure measureFirst; private final PathMeasure measureSecond; private final float lengthFirst; private final float lengthSecond; private JoinedPath(Path pathFirst, Path pathSecond) { //PathMeasure类用于提供路径上的点坐标 measureFirst = new PathMeasure(pathFirst, false); measureSecond = new PathMeasure(pathSecond, false); lengthFirst = measureFirst.getLength(); lengthSecond = measureSecond.getLength(); }