PathMeasure的方法：

setPath(Path path,  boolean forceClosed)/*计算长度的时候是否自动封闭路径*/)
 /*计算路径的总长度*/
getLength()
/*计算距离路径起始点distance的位置的坐标和该点的正切值*/
getPosTan(float distance, float pos[], float tan[])
/*计算距离路径起始点distance的位置的坐标的矩阵*/
getMatrix(float distance, Matrix matrix, int flags)
/*从路径中截取距离起始点startD到stopD的新路径到dst中*/
 getSegment(float startD, float stopD, Path dst, boolean startWithMoveTo/*是否将起始点移动到startD的位置*/)
/*路径是否是闭合路径*/
isClosed()
/*该路径中的下一个路径*/
nextContour()

附上一个小例子：

package edo.com.design.view;

import android.animation.Animator;
import android.animation.ValueAnimator;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PathMeasure;
import android.graphics.RectF;
import android.os.Handler;
import android.os.Message;
import android.util.AttributeSet;
import android.view.View;

public class SearchView extends View {

    private Paint mPaint;
    private Path mSearchPath, mProgressPath;
    private PathMeasure mMeasure;
    // 当前的状态
    private State mCurrentState;
    private float mAnimatorValue = 0;

    // 动画时间
    private int mDefaultDuration;

    private ValueAnimator mStartAnimator, mSearchAnimator, mEndAnimator;

    public SearchView(Context context) {
        this(context, null);
    }

    public SearchView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public SearchView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    // 初始化
    private void init() {
        initPaint();
        setupPath();
        initAnimationListener();
        mCurrentState = State.NONE;
        startSearch();
    }

    // 开始搜索
    public void startSearch() {
        mHandler.sendEmptyMessage(0);
    }

    // 初始化动画监听器
    private void initAnimationListener() {
        mDefaultDuration = 2000;

        mStartAnimator = ValueAnimator.ofFloat(0, 1.0f).setDuration(mDefaultDuration);
        mStartAnimator.addUpdateListener(mUpdateListener);
        mStartAnimator.addListener(mAnimatorListener);

        mSearchAnimator = ValueAnimator.ofFloat(1.0f, 0).setDuration(mDefaultDuration);
        mSearchAnimator.setRepeatCount(2);
        mSearchAnimator.addUpdateListener(mUpdateListener);
        mSearchAnimator.addListener(mAnimatorListener);

        mEndAnimator = ValueAnimator.ofFloat(1.0f, 0).setDuration(mDefaultDuration);
        mEndAnimator.addUpdateListener(mUpdateListener);
        mEndAnimator.addListener(mAnimatorListener);
    }

    // 动画值变化监听
    private ValueAnimator.AnimatorUpdateListener mUpdateListener = new ValueAnimator.AnimatorUpdateListener() {
        @Override
        public void onAnimationUpdate(ValueAnimator animation) {
            mAnimatorValue = (float) animation.getAnimatedValue();
            postInvalidate();
        }
    };

    // 动画监听
    private ValueAnimator.AnimatorListener mAnimatorListener = new ValueAnimator.AnimatorListener() {

        @Override
        public void onAnimationStart(Animator animation) {

        }

        @Override
        public void onAnimationEnd(Animator animation) {
            mHandler.sendEmptyMessage(0);
        }

        @Override
        public void onAnimationCancel(Animator animation) {

        }

        @Override
        public void onAnimationRepeat(Animator animation) {

        }
    };

    // 初始化画笔
    private void initPaint() {
        mPaint = new Paint();
        mPaint.setColor(Color.WHITE);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeWidth(8);
        mPaint.setAntiAlias(true);
        // 路径计算器
        mMeasure = new PathMeasure();
    }

    // 初始化路径
    private void setupPath() {
        // 进度条的路径
        mProgressPath = new Path();
        RectF r1 = new RectF(-100, -100, 100, 100);
        mProgressPath.addArc(r1, 45, 359.9f);

        // 放大镜的路径
        mSearchPath = new Path();
        RectF r2 = new RectF(-50, -50, 50, 50);
        mSearchPath.addArc(r2, 45, 359.9f);
        // 放大镜的手柄，连接到进度条的原点
        float[] pos = new float[2];
        mMeasure.setPath(mProgressPath, false);
        mMeasure.getPosTan(0, pos, null);
        mSearchPath.lineTo(pos[0], pos[1]);
    }

    // 动画控制器
    private Handler mHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            switch (mCurrentState) {
                case NONE:
                    mCurrentState = State.STARTING;
                    mStartAnimator.start();
                    break;
                case STARTING:
                    mCurrentState = State.SEARCHING;
                    mSearchAnimator.start();
                    break;
                case SEARCHING:
                    mCurrentState = State.END;
                    mEndAnimator.start();
                    break;
                case END:
                    mCurrentState = State.NONE;
                    break;
            }
        }
    };

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.translate(getWidth() / 2, getHeight() / 2);
        canvas.drawColor(Color.parseColor("#0082D7"));
        float length = 0, start = 0, end = 0;
        Path destPath = new Path();
        switch (mCurrentState) {
            case NONE:
                destPath = mSearchPath;
                break;
            case STARTING:
                mMeasure.setPath(mSearchPath, false);
                length = mMeasure.getLength();
                mMeasure.getSegment(mAnimatorValue * length, length, destPath, true);
                break;
            case SEARCHING:
                mMeasure.setPath(mProgressPath, false);
                end = mMeasure.getLength() * mAnimatorValue;
                start = end - (mAnimatorValue > 0.5f ? 1 - mAnimatorValue : mAnimatorValue) * 200.0f;
                mMeasure.getSegment(start, end, destPath, true);
                break;
            case END:
                mMeasure.setPath(mSearchPath, false);
                length = mMeasure.getLength();
                mMeasure.getSegment(mAnimatorValue * length, length, destPath, true);
                break;
        }
        canvas.drawPath(destPath, mPaint);
    }

    private enum State {
        NONE, STARTING, SEARCHING, END
    }
}