Android自定义动画系列六，今天来分享第六个自定义Loading动画（ElasticBallBuilder），我给他起了一个逼格很高的名字，叫颤抖吧！球球，这个动画让我绞尽脑汁，算数算的晕乎乎，不过结果还是很满意的，还是老规矩先介绍，效果图在最后面。
实现效果图在最后，GIF有点大，手机流量请三思。
⭐️这里我想问大家一个问题，这个最终效果图，是放在文章的 开头 好呢？还是放在 结尾 好呢？
大家评论里面给个建议吧。谢谢了。
介绍
首先依旧是声明，做这些动画的初衷是为了学习和分享，所以希望大家可以指点错误，让我更好的进步。（系列加载动画的截止时间：我放弃的时候）。
上一个动画链接：Android自定义加载动画-PacMan
正文
参数变量初始化，用处我都在代码里写了注释了，不懂得大家也可以问，有什么不对的，也希望大家帮忙指出，谢谢了。如下：
//动画间隔时间
private static final long DURATION_TIME = 333;
//最终阶段
private static final int FINAL_STATE = 2;
//小球共5个位置
private static final int SUM_POINT_POS = 5;
//贝塞尔曲线常量
private static final float PROP_VALUE = 0.551915024494f;
//小球点集合
private final LinkedList<CirclePoint> mBallPoints = new LinkedList<>();
//背景圆集合
private final LinkedList<CirclePoint> mBGCircles = new LinkedList<>();
private Paint mPaint;
private float mBallR;
private Path mPath;
//当前动画阶段
private int mCurrAnimatorState = 0;
//每个小球的偏移量
private float mCanvasTranslateOffset;
//当前状态是否翻转
private boolean mIsReverse = false;
//当前小球的位置
private int mCurrPointPos = 0;
首先初始化参数，mBallR 为小球半径，mCanvasTranslateOffset 为小球之间的间距，mPath 路径，其它如注释：
@Override
protected void initParams(Context context)
{
mBallR = getAllSize() / SUM_POINT_POS;
mCanvasTranslateOffset = getIntrinsicWidth() / SUM_POINT_POS;
mPath = new Path();
initPaint(5);
initPoints();
initBGPoints();
}
/**
* 背景圆点初始化
*/
private void initBGPoints()
{
float centerX = getViewCenterX();
float centerY = getViewCenterY();
CirclePoint p_0 = new CirclePoint(centerX - mCanvasTranslateOffset * 2, centerY);
CirclePoint p_1 = new CirclePoint(centerX - mCanvasTranslateOffset, centerY);
CirclePoint p_2 = new CirclePoint(centerX, centerY);
CirclePoint p_3 = new CirclePoint(centerX + mCanvasTranslateOffset, centerY);
CirclePoint p_4 = new CirclePoint(centerX + mCanvasTranslateOffset * 2, centerY);
p_0.setEnabled(false);//默认第一个圆不显示
mBGCircles.add(p_0);
mBGCircles.add(p_1);
mBGCircles.add(p_2);
mBGCircles.add(p_3);
mBGCircles.add(p_4);
}
这里很重要，很重要，重要。
这里初始化的是小球的各个点坐标，这里的小球是通过贝塞尔曲线绘制了，为了后面方便动画操作，所以球的绘制就会相对的繁琐了。
贝塞尔曲线画球的原理，如下：
原理图，来自其它地方
具体标注点，请对照我注释中的P0～P11点，如下：
/**
* p10 p9 p8
* ------ ------
* p11 p7
* | |
* | |
* p0 | (0,0) | p6
* | |
* | |
* p1 p5
* ------ ------
* p2 p3 p4
*/
private void initPoints()
{
float centerX = getViewCenterX();
float centerY = getViewCenterY();
CirclePoint p_0 = new CirclePoint(centerX - mBallR, centerY);
mBallPoints.add(p_0);
CirclePoint p_1 = new CirclePoint(centerX - mBallR, centerY + mBallR * PROP_VALUE);
mBallPoints.add(p_1);
CirclePoint p_2 = new CirclePoint(centerX - mBallR * PROP_VALUE, centerY + mBallR);
mBallPoints.add(p_2);
CirclePoint p_3 = new CirclePoint(centerX, centerY + mBallR);
mBallPoints.add(p_3);
CirclePoint p_4 = new CirclePoint(centerX + mBallR * PROP_VALUE, centerY + mBallR);
mBallPoints.add(p_4);
CirclePoint p_5 = new CirclePoint(centerX + mBallR, centerY + mBallR * PROP_VALUE);
mBallPoints.add(p_5);
CirclePoint p_6 = new CirclePoint(centerX + mBallR, centerY);
mBallPoints.add(p_6);
CirclePoint p_7 = new CirclePoint(centerX + mBallR, centerY - mBallR * PROP_VALUE);
mBallPoints.add(p_7);
CirclePoint p_8 = new CirclePoint(centerX + mBallR * PROP_VALUE, centerY - mBallR);
mBallPoints.add(p_8);
CirclePoint p_9 = new CirclePoint(centerX, centerY - mBallR);
mBallPoints.add(p_9);
CirclePoint p_10 = new CirclePoint(centerX - mBallR * PROP_VALUE, centerY - mBallR);
mBallPoints.add(p_10);
CirclePoint p_11 = new CirclePoint(centerX - mBallR, centerY - mBallR * PROP_VALUE);
mBallPoints.add(p_11);
}
/**
* 初始化画笔
*/
private void initPaint(float lineWidth)
{
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
mPaint.setStrokeWidth(lineWidth);
mPaint.setColor(Color.BLACK);
mPaint.setDither(true);
mPaint.setFilterBitmap(true);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeJoin(Paint.Join.ROUND);
}
以下，开始了绘制工作了，drawBG() 绘制背景，在这里就不多介绍了；我们看下 drawBall() 方法，通过路径贝塞尔曲线绘制并连接一开始初始化的12个点坐标形成路径，最终绘制到画布上。
@Override
protected void onDraw(Canvas canvas)
{
drawBG(canvas);
drawBall(canvas);
}
/**
* 绘制小球
*
* @param canvas
*/
private void drawBall(Canvas canvas)
{
canvas.save();
mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
float offsetX = mBGCircles.size() / 2 * mCanvasTranslateOffset;
canvas.translate(-offsetX + mCanvasTranslateOffset * mCurrPointPos, 0);
mPath.reset();
mPath.moveTo(mBallPoints.get(0).getX(), mBallPoints.get(0).getY());
mPath.cubicTo(mBallPoints.get(1).getX(), mBallPoints.get(1).getY(), mBallPoints.get(2).getX(), mBallPoints.get(2).getY(), mBallPoints.get(3).getX(), mBallPoints.get(3).getY());
mPath.cubicTo(mBallPoints.get(4).getX(), mBallPoints.get(4).getY(), mBallPoints.get(5).getX(), mBallPoints.get(5).getY(), mBallPoints.get(6).getX(), mBallPoints.get(6).getY());
mPath.cubicTo(mBallPoints.get(7).getX(), mBallPoints.get(7).getY(), mBallPoints.get(8).getX(), mBallPoints.get(8).getY(), mBallPoints.get(9).getX(), mBallPoints.get(9).getY());
mPath.cubicTo(mBallPoints.get(10).getX(), mBallPoints.get(10).getY(), mBallPoints.get(11).getX(), mBallPoints.get(11).getY(), mBallPoints.get(0).getX(), mBallPoints.get(0).getY());
canvas.drawPath(mPath, mPaint);
canvas.restore();
}
/**
* 绘制背景圆
*
* @param canvas
*/
private void drawBG(Canvas canvas)
{
canvas.save();
mPaint.setStyle(Paint.Style.STROKE);
for (CirclePoint point : mBGCircles)
{
point.draw(canvas, mBallR, mPaint);
}
canvas.restore();
}
这里是不同阶段对应的不同偏移量赋值，前三个阶段是针对顺序移动的操作，后三个阶段是对应的逆序时所需要的赋值操作，所有位移操作都是对小球的12点进行X轴方向的处理。
@Override
protected void computeUpdateValue(ValueAnimator animation, @FloatRange(from = 0.0, to = 1.0) float animatedValue)
{
float offset = mCanvasTranslateOffset;
int currState = mIsReverse ? mCurrAnimatorState + 3 : mCurrAnimatorState;
switch (currState)
{
case 0:
animation.setDuration(DURATION_TIME);
animation.setInterpolator(new AccelerateInterpolator());
mBallPoints.get(5).setOffsetX(animatedValue * offset);
mBallPoints.get(6).setOffsetX(animatedValue * offset);
mBallPoints.get(7).setOffsetX(animatedValue * offset);
break;
case 1:
animation.setDuration(DURATION_TIME + 111);
animation.setInterpolator(new DecelerateInterpolator());
mBallPoints.get(2).setOffsetX(animatedValue * offset);
mBallPoints.get(3).setOffsetX(animatedValue * offset);
mBallPoints.get(4).setOffsetX(animatedValue * offset);
mBallPoints.get(8).setOffsetX(animatedValue * offset);
mBallPoints.get(9).setOffsetX(animatedValue * offset);
mBallPoints.get(10).setOffsetX(animatedValue * offset);
break;
case 2:
animation.setDuration(DURATION_TIME + 333);
animation.setInterpolator(new BounceInterpolator());
mBallPoints.get(0).setOffsetX(animatedValue * offset);
mBallPoints.get(1).setOffsetX(animatedValue * offset);
mBallPoints.get(11).setOffsetX(animatedValue * offset);
break;
case 3:
animation.setDuration(DURATION_TIME);
animation.setInterpolator(new AccelerateInterpolator());
mBallPoints.get(0).setOffsetX((1 - animatedValue) * offset);
mBallPoints.get(1).setOffsetX((1 - animatedValue) * offset);
mBallPoints.get(11).setOffsetX((1 - animatedValue) * offset);
break;
case 4:
animation.setDuration(DURATION_TIME + 111);
animation.setInterpolator(new DecelerateInterpolator());
mBallPoints.get(2).setOffsetX((1 - animatedValue) * offset);
mBallPoints.get(3).setOffsetX((1 - animatedValue) * offset);
mBallPoints.get(4).setOffsetX((1 - animatedValue) * offset);
mBallPoints.get(8).setOffsetX((1 - animatedValue) * offset);
mBallPoints.get(9).setOffsetX((1 - animatedValue) * offset);
mBallPoints.get(10).setOffsetX((1 - animatedValue) * offset);
break;
case 5:
animation.setDuration(DURATION_TIME + 333);
animation.setInterpolator(new BounceInterpolator());
mBallPoints.get(5).setOffsetX((1 - animatedValue) * offset);
mBallPoints.get(6).setOffsetX((1 - animatedValue) * offset);
mBallPoints.get(7).setOffsetX((1 - animatedValue) * offset);
break;
}
}
在下面的方法中，对小球动画的各个阶段进行分布，各个点的偏移量进行重置，以及顺序倒序移动的切换逻辑进行判断，并且对背景圆也做了关联处理。
@Override
public void onAnimationRepeat(Animator animation)
{
if (++mCurrAnimatorState > FINAL_STATE)
{//还原到第一阶段
mCurrAnimatorState = 0;
/* 小球位置改变 */
if (mIsReverse)
{//倒序
mCurrPointPos--;
}
else
{//顺序
mCurrPointPos++;
}
/* 重置并翻转动画过程 */
if (mCurrPointPos >= SUM_POINT_POS - 1)
{//倒序
mIsReverse = true;
mCurrPointPos = SUM_POINT_POS - 2;//I Don't Know
for (int i = 0; i < mBGCircles.size(); i++)
{
CirclePoint point = mBGCircles.get(i);
if (i == mBGCircles.size() - 1)
{
point.setEnabled(true);
}
else
{
point.setEnabled(false);
}
}
}
else if (mCurrPointPos < 0)
{//顺序
mIsReverse = false;
mCurrPointPos = 0;
for (int i = 0; i < mBGCircles.size(); i++)
{
CirclePoint point = mBGCircles.get(i);
if (i == 0)
{
point.setEnabled(false);
}
else
{
point.setEnabled(true);
}
}
}
//每个阶段恢复状态，以及对背景圆的控制
if (mIsReverse)
{//倒序
//恢复状态
for (CirclePoint point : mBallPoints)
{
point.setOffsetX(mCanvasTranslateOffset);
}
mBGCircles.get(mCurrPointPos + 1).setEnabled(true);
}
else
{//顺序
//恢复状态
for (CirclePoint point : mBallPoints)
{
point.setOffsetX(0);
}
mBGCircles.get(mCurrPointPos).setEnabled(false);
}
}
}
圆点的内部类，封装了此动画中所涉及到的点和球的参数信息（小球的点与背景球都是复用此类的）
/**
* 圆点内部类
*/
private class CirclePoint
{
private final float mX;
private final float mY;
private float mOffsetX = 0;
private float mOffsetY = 0;
private boolean mEnabled = true;
CirclePoint(float x, float y)
{
mX = x;
mY = y;
}
float getX()
{
return mX + mOffsetX;
}
float getY()
{
return mY + mOffsetY;
}
void setOffsetX(float offsetX)
{
mOffsetX = offsetX;
}
void setOffsetY(float offsetY)
{
mOffsetY = offsetY;
}
public void setEnabled(boolean enabled)
{
mEnabled = enabled;
}
void draw(Canvas canvas, float r, Paint paint)
{
if (this.mEnabled)
{
canvas.drawCircle(this.getX(), this.getY(), r, paint);
}
}
}
总结
小伙伴们，介绍就到这里了，要是想看更多细节，可以前往文章最下面的Github链接，如果大家觉得ok的话，希望能给个喜欢，最渴望的是在Github上给个star。谢谢了。
如果大家有什么更好的方案，或者想要实现的加载效果，可以给我留言或者私信我，我会想办法实现出来给大家。谢谢支持。
演示
动画效果演示
Github：zyao89/ZCustomView
作者：Zyao89；转载请保留此行，谢谢；
个人博客：https://zyao89.cn
