利用pathMeasure实现路径动画

package com.loaderman.customviewdemo;

import android.animation.ValueAnimator;
import android.content.Context;
import android.graphics.*;
import android.util.AttributeSet;
import android.view.View;

public class GetSegmentView extends View {

    private Path mCirclePath, mDstPath;
    private Paint mPaint;
    private PathMeasure mPathMeasure;
    private Float mCurAnimValue;

    public GetSegmentView(Context context, AttributeSet attrs) {
        super(context, attrs);
        setLayerType(LAYER_TYPE_SOFTWARE, null);

        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeWidth(4);
        mPaint.setColor(Color.BLACK);

        mDstPath = new Path();
        mCirclePath = new Path();
        mCirclePath.addCircle(100, 100, 50, Path.Direction.CW);

        mPathMeasure = new PathMeasure(mCirclePath, true);

        ValueAnimator animator = ValueAnimator.ofFloat(0, 1);
        animator.setRepeatCount(ValueAnimator.INFINITE);
        animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            public void onAnimationUpdate(ValueAnimator animation) {
                mCurAnimValue = (Float) animation.getAnimatedValue();
                invalidate();
            }
        });
        animator.setDuration(2000);
        animator.start();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        float length = mPathMeasure.getLength();
        float stop = length * mCurAnimValue;
        float start = (float) (stop - ((0.5 - Math.abs(mCurAnimValue - 0.5)) * length));
        mDstPath.reset();
        canvas.drawColor(Color.WHITE);
        mPathMeasure.getSegment(start, stop, mDstPath, true);//用于截取整个path中某个片段,通过参数startD和stopD来控制截取的长度,并将截取后的path保存到参数dst中,最后一个参数表示起始点是否使用moveTo将路径的新起始点移到结果path的起始点中,通常设置为true

//        mPathMeasure.getSegment(0, stop, mDstPath, true);
        canvas.drawPath(mDstPath, mPaint);
    }
}

package com.loaderman.customviewdemo;

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.util.AttributeSet;
import android.view.View;

public class AliPayView extends View {
    private Path mCirclePath, mDstPath;
    private Paint mPaint;
    private PathMeasure mPathMeasure;
    private Float mCurAnimValue;
    private int mCentX = 100;
    private int mCentY = 100;
    private int mRadius = 50;

    public AliPayView(Context context, AttributeSet attrs) {
        super(context, attrs);
        setLayerType(LAYER_TYPE_SOFTWARE, null);

        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeWidth(4);
        mPaint.setColor(Color.BLACK);

        mDstPath = new Path();
        mCirclePath = new Path();

        mCirclePath.addCircle(mCentX, mCentY, mRadius, Path.Direction.CW);

        mCirclePath.moveTo(mCentX - mRadius / 2, mCentY);
        mCirclePath.lineTo(mCentX, mCentY + mRadius / 2);
        mCirclePath.lineTo(mCentX + mRadius / 2, mCentY - mRadius / 3);

        mPathMeasure = new PathMeasure(mCirclePath, false);

        ValueAnimator animator = ValueAnimator.ofFloat(0, 2);
        animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            public void onAnimationUpdate(ValueAnimator animation) {
                mCurAnimValue = (Float) animation.getAnimatedValue();
                invalidate();
            }
        });
        animator.setDuration(4000);
        animator.start();
    }

    boolean mNext = false;

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawColor(Color.WHITE);

        if (mCurAnimValue < 1) {
            float stop = mPathMeasure.getLength() * mCurAnimValue;
            mPathMeasure.getSegment(0, stop, mDstPath, true);
        } else {
            if (!mNext) {
                mNext = true;
                mPathMeasure.getSegment(0, mPathMeasure.getLength(), mDstPath, true);
                mPathMeasure.nextContour();  //跳转到下一条曲线函数
            }
            float stop = mPathMeasure.getLength() * (mCurAnimValue - 1);
            mPathMeasure.getSegment(0, stop, mDstPath, true);
        }
        canvas.drawPath(mDstPath, mPaint);
    }
}

package com.loaderman.customviewdemo;

import android.animation.ValueAnimator;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PathMeasure;
import android.util.AttributeSet;
import android.view.View;

public class GetPosTanView extends View {
    private Path mCirclePath, mDstPath;
    private Paint mPaint;
    private PathMeasure mPathMeasure;
    private Float mCurAnimValue;
    private Bitmap mArrawBmp;
    private float[] pos = new float[2];
    private float[] tan = new float[2];

    public GetPosTanView(Context context, AttributeSet attrs) {
        super(context, attrs);
        setLayerType(LAYER_TYPE_SOFTWARE, null);
        mArrawBmp = BitmapFactory.decodeResource(getResources(), R.drawable.arraw);
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeWidth(4);
        mPaint.setColor(Color.BLACK);

        mDstPath = new Path();
        mCirclePath = new Path();
        mCirclePath.addCircle(100, 100, 50, Path.Direction.CW);

        mPathMeasure = new PathMeasure(mCirclePath, true);//true计算的path的闭合长度,false则测量当前path状态长度

        ValueAnimator animator = ValueAnimator.ofFloat(0, 1);
        animator.setRepeatCount(ValueAnimator.INFINITE);//无限循环
        animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            public void onAnimationUpdate(ValueAnimator animation) {
                mCurAnimValue = (Float) animation.getAnimatedValue();
                invalidate();
            }
        });
        animator.setDuration(2000);
        animator.start();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        canvas.drawColor(Color.WHITE);
        float length = mPathMeasure.getLength();  //计算路径长度
        float stop = length * mCurAnimValue;
        mDstPath.reset();

        mPathMeasure.getSegment(0, stop, mDstPath, true);
        canvas.drawPath(mDstPath, mPaint);

        /**
         * 箭头旋转、位移实现方式一：
         */

        //计算方位角
//        mPathMeasure.getPosTan(stop, pos, tan);//用于得到路径上某一长度的位置,以及位置的证正切值
//        float degrees = (float) (Math.atan2(tan[1], tan[0]) * 180.0 / Math.PI);
//        Matrix matrix = new Matrix();
//        matrix.postRotate(degrees, mArrawBmp.getWidth() / 2, mArrawBmp.getHeight() / 2);
//        matrix.postTranslate(pos[0] - mArrawBmp.getWidth() / 2, pos[1] - mArrawBmp.getHeight() / 2);

        /**
         * 箭头旋转、位移实现方式一：
         */
        Matrix matrix = new Matrix();
        mPathMeasure.getMatrix(stop, matrix, PathMeasure.POSITION_MATRIX_FLAG | PathMeasure.TANGENT_MATRIX_FLAG);//用于的到路径上某一长度的位置以及该位置的正切值的矩阵
        matrix.preTranslate(-mArrawBmp.getWidth() / 2, -mArrawBmp.getHeight() / 2);
        canvas.drawBitmap(mArrawBmp, matrix, mPaint);
    }

}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">

    <com.loaderman.customviewdemo.GetSegmentView
        android:layout_width="match_parent"
        android:layout_height="80dp"/>
    <com.loaderman.customviewdemo.AliPayView
        android:layout_width="match_parent"
        android:layout_height="80dp"/>
    <com.loaderman.customviewdemo.GetPosTanView
        android:layout_width="match_parent"
        android:layout_height="150dp"/>
</LinearLayout>

效果