Android动画之旅(三)----6个小球移动的轨迹动画

动画组成:1.贝塞尔曲线和PathMeasure结合使用。2. mPathMeasure.getPosTan（float v,float [] pos ,float[] tan）的使用。3.通过动画0到1形成轨迹动画。

package com.example.administrator.animationworkdemo.views;import android.animation.Animator;import android.animation.AnimatorListenerAdapter;import android.animation.ValueAnimator;import android.content.Context;import android.graphics.Canvas;import android.graphics.Paint;import android.graphics.Path;import android.graphics.PathMeasure;import android.util.AttributeSet;import android.view.View;import android.view.animation.DecelerateInterpolator;/** * Created by SuperD on 2017/2/18. * 小球加载的运动轨迹 */public class BallLoadingPathView extends View implements View.OnClickListener {    private static final int POINT_DISTANCE = 50;    private static final int ANIM_RUNNING_TIME = 1000;    //小球相关的描述    private int mPointCount = 6;    private int mPointRadius = 20;    //中心点    private int centerX;    private int centerY;    //首尾点之前的长度(加上隐藏的那个点,实际上有7个点)    private float mWidth;    //起始点,结束点    private float mPointStartX;    private float mPointEndX;    private float mPointY;    //绘制路径    private PathMeasure mPathMeasure;    //储存在路径移动过程中的点    private float[] mPos = new float[2];    private Path mPath;    private float mPathLength;    //轨迹动画的比率    private float mPathRatio;    private Paint mPaint;    private ValueAnimator mPathAnim;    //小球运动的标签  True的时候mPointFlag--向下 False的时候mPointFlag--- 向上    private int mPointFlag = 1;    public BallLoadingPathView(Context context) {        this(context, null);    }    public BallLoadingPathView(Context context, AttributeSet attrs) {        this(context, attrs, 0);    }    public BallLoadingPathView(Context context, AttributeSet attrs, int defStyleAttr) {        super(context, attrs, defStyleAttr);        init();    }    private void init() {        mPathMeasure = new PathMeasure();        mPath = new Path();        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);        mPaint.setStyle(Paint.Style.FILL_AND_STROKE);        mPaint.setStrokeWidth(5);        mPathAnim = ValueAnimator.ofFloat(0, 1);        mPathAnim.setDuration(ANIM_RUNNING_TIME);        mPathAnim.setRepeatCount(ValueAnimator.INFINITE);        mPathAnim.setInterpolator(new DecelerateInterpolator());        mPathAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {            @Override            public void onAnimationUpdate(ValueAnimator valueAnimator) {                mPathRatio = (float) valueAnimator.getAnimatedValue();                invalidate();            }        });        mPathAnim.addListener(new AnimatorListenerAdapter() {            @Override            public void onAnimationRepeat(Animator animation) {                super.onAnimationRepeat(animation);                mPointFlag = -mPointFlag;            }        });        setOnClickListener(this);    }    @Override    protected void onSizeChanged(int w, int h, int oldw, int oldh) {        super.onSizeChanged(w, h, oldw, oldh);        centerX = w / 2;        centerY = h / 2;        mWidth = (mPointCount - 1) * mPointRadius * 2 + (mPointCount - 1) * POINT_DISTANCE;        mPointStartX = centerX - mWidth / 2;        mPointEndX = centerX + mWidth / 2;        mPointY = centerY;        mPath.moveTo(mPointStartX, mPointY);        mPath.quadTo(centerX, centerY + mWidth / 2, mPointEndX, mPointY);        mPathMeasure.setPath(mPath, false);        mPathLength = mPathMeasure.getLength();    }    @Override    protected void onDraw(Canvas canvas) {        super.onDraw(canvas);        for (int i = 0; i < mPointCount; i++) {            if (i == 0) {                mPathMeasure.getPosTan(mPathRatio * mPathLength, mPos, null);                if (mPointFlag == 1) {                    canvas.drawCircle(mPos[0], mPos[1], mPointRadius, mPaint);                } else {                    canvas.drawCircle(mPos[0], getSymmetryPointY(mPos[1]), mPointRadius, mPaint);                }            } else {                float startPoint = mPointStartX + (POINT_DISTANCE + 2 * mPointRadius) * i;                canvas.drawCircle(                        startPoint - (POINT_DISTANCE + 2 * mPointRadius) * mPathRatio,                        mPointY,                        mPointRadius, mPaint);            }        }    }    /**     * 获得当前Y坐标关于屏幕中心Y轴的对称点     *     * @param pointY     * @return     */    private float getSymmetryPointY(float pointY) {        float symmetryPointY = 2 * centerY - pointY;        return symmetryPointY;    }    @Override    public void onClick(View view) {        mPathAnim.start();    }}