项目地址：https://github.com/JeasonWong/SlackLoadingView
老规矩，先上效果。
图好大。。
说下第一眼看到这个动画后的思路：
+两根平行线，要用到直线方程 y=kx+b
+另外两根平行线，与之前两根平行线的斜率相乘为-1，即k1*k2=-1
+线条做圆周运动就是k值的不断变化
+然后就是简单的线条长度变化
我相信很多人第一眼会和我有类似的思路，但是当我上了个厕所后意识到我想复杂了~
说下上完厕所后的思路：
不要想着线条是斜的，就是一个普通的线段，一个LineTo搞定（startX和stopX一样，仅Y不同）
线条的垂直更容易，直接Canvas翻转（转过后再转回）
整个动画的圆周运动也是Canvas翻转（转过后不转回）
线条的单度变化依然用属性动画（这是必须的。。）
动画开始前就让整个Canvas旋转
这样一来就太容易了。
我把动画分成了四步：
画布旋转及线条变化动画（Canvas Rotate Line Change）
画布旋转动画（Canvas Rotate）
画布旋转圆圈变化动画（Canvas Rotate Circle Change）
线条变化动画（Line Change）
详细说明前先介绍下成员变量和一些初始化
成员变量
//静止状态 private final int STATUS_STILL = 0; //加载状态 private final int STATUS_LOADING = 1; //线条最大长度 private final int MAX_LINE_LENGTH = dp2px(getContext(), 120); //线条最短长度 private final int MIN_LINE_LENGTH = dp2px(getContext(), 40); //最大间隔时长 private final int MAX_DURATION = 3000; //最小间隔时长 private final int MIN_DURATION = 500; private Paint mPaint; private int[] mColors = new int[]{0xB07ECBDA, 0xB0E6A92C, 0xB0D6014D, 0xB05ABA94}; private int mWidth, mHeight; //动画间隔时长 private int mDuration = MIN_DURATION; //线条总长度 private int mEntireLineLength = MIN_LINE_LENGTH; //圆半径 private int mCircleRadius; //所有动画 private List<Animator> mAnimList = new ArrayList<>(); //Canvas起始旋转角度 private final int CANVAS_ROTATE_ANGLE = 60; //动画当前状态 private int mStatus = STATUS_STILL; //Canvas旋转角度 private int mCanvasAngle; //线条长度 private float mLineLength; //半圆Y轴位置 private float mCircleY; //第几部动画 private int mStep;
初始化
private void initView() { mPaint = new Paint(); mPaint.setAntiAlias(true); mPaint.setColor(mColors[0]); } private void initData() { mCanvasAngle = CANVAS_ROTATE_ANGLE; mLineLength = mEntireLineLength; mCircleRadius = mEntireLineLength / 5; mPaint.setStrokeWidth(mCircleRadius * 2); mStep = 0; }
一、画布旋转及线条变化动画（Canvas Rotate Line Change）
/** * Animation1 * 动画1 * Canvas Rotate Line Change * 画布旋转及线条变化动画 */ private void startCRLCAnim() { Collection<Animator> animList = new ArrayList<>(); ValueAnimator canvasRotateAnim = ValueAnimator.ofInt(CANVAS_ROTATE_ANGLE + 0, CANVAS_ROTATE_ANGLE + 360); canvasRotateAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() { @Override public void onAnimationUpdate(ValueAnimator animation) { mCanvasAngle = (int) animation.getAnimatedValue(); } }); animList.add(canvasRotateAnim); ValueAnimator lineWidthAnim = ValueAnimator.ofFloat(mEntireLineLength, -mEntireLineLength); lineWidthAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() { @Override public void onAnimationUpdate(ValueAnimator animation) { mLineLength = (float) animation.getAnimatedValue(); invalidate(); } }); animList.add(lineWidthAnim); AnimatorSet animationSet = new AnimatorSet(); animationSet.setDuration(mDuration); animationSet.playTogether(animList); animationSet.setInterpolator(new LinearInterpolator()); animationSet.addListener(new AnimatorListener() { @Override public void onAnimationEnd(Animator animation) { Log.d("@=>", "动画1结束"); if (mStatus == STATUS_LOADING) { mStep++; startCRAnim(); } } }); animationSet.start(); mAnimList.add(animationSet); }
第一步动画涉及到两个动画同时进行，所以使用了AnimatorSet，这个类很强大，可以让N个动画同时进行（playTogether），也可以让N个动画顺序执行（playSequentially）。
说到这里，其实我的四个动画就是顺序进行的，但是每个动画里又有同时进行的动画，为了讲解方便，我是监听了onAnimationEnd来控制动画执行顺序，其实可以直接使用playSequentially。
上方动画就干了两件事：
1、旋转画布，从CANVAS_ROTATE_ANGLE + 0转到CANVAS_ROTATE_ANGLE + 360，CANVAS_ROTATE_ANGLE是画布初始倾斜角度
2、线条长度变化，从mEntireLineLength到-mEntireLineLength。
对应的onDraw方法：
@Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); switch (mStep % 4) { case 0: for (int i = 0; i < mColors.length; i++) { mPaint.setColor(mColors[i]); drawCRLC(canvas, mWidth / 2 - mEntireLineLength / 2.2f, mHeight / 2 - mLineLength, mWidth / 2 - mEntireLineLength / 2.2f, mHeight / 2 + mEntireLineLength, mPaint, mCanvasAngle + i * 90); } break; ... } } ... private void drawCRLC(Canvas canvas, float startX, float startY, float stopX, float stopY, @NonNull Paint paint, int rotate) { canvas.rotate(rotate, mWidth / 2, mHeight / 2); canvas.drawArc(new RectF(startX - mCircleRadius, startY - mCircleRadius, startX + mCircleRadius, startY + mCircleRadius), 180, 180, true, mPaint); canvas.drawLine(startX, startY, stopX, stopY, paint); canvas.drawArc(new RectF(stopX - mCircleRadius, stopY - mCircleRadius, stopX + mCircleRadius, stopY + mCircleRadius), 0, 180, true, mPaint); canvas.rotate(-rotate, mWidth / 2, mHeight / 2); }
是不是很机智，drawCRLC做了三件事：
1、画布旋转后又旋转回来
2、画半圆（为什么要画半圆？不画整个圆？这里留个思考题。）
3、画线条
这样动画1就完成了。
二、画布旋转动画（Canvas Rotate）
/** * Animation2 * 动画2 * Canvas Rotate * 画布旋转动画 */ private void startCRAnim() { ValueAnimator canvasRotateAnim = ValueAnimator.ofInt(mCanvasAngle, mCanvasAngle + 180); canvasRotateAnim.setDuration(mDuration / 2); canvasRotateAnim.setInterpolator(new LinearInterpolator()); canvasRotateAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() { @Override public void onAnimationUpdate(ValueAnimator animation) { mCanvasAngle = (int) animation.getAnimatedValue(); invalidate(); } }); canvasRotateAnim.addListener(new AnimatorListener() { @Override public void onAnimationEnd(Animator animation) { Log.d("@=>", "动画2结束"); if (mStatus == STATUS_LOADING) { mStep++; startCRCCAnim(); } } }); canvasRotateAnim.start(); mAnimList.add(canvasRotateAnim); } ... @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); switch (mStep % 4) { ... case 1: for (int i = 0; i < mColors.length; i++) { mPaint.setColor(mColors[i]); drawCR(canvas, mWidth / 2 - mEntireLineLength / 2.2f, mHeight / 2 + mEntireLineLength, mPaint, mCanvasAngle + i * 90); } break; ... } } ... private void drawCR(Canvas canvas, float x, float y, @NonNull Paint paint, int rotate) { canvas.rotate(rotate, mWidth / 2, mHeight / 2); canvas.drawCircle(x, y, mCircleRadius, paint); canvas.rotate(-rotate, mWidth / 2, mHeight / 2); }
有了动画1的底子，那这个就太容易了，只是简单的旋转Canvas。
三、画布旋转圆圈变化动画（Canvas Rotate Circle Change）
/** * Animation3 * 动画3 * Canvas Rotate Circle Change * 画布旋转圆圈变化动画 */ private void startCRCCAnim() { Collection<Animator> animList = new ArrayList<>(); ValueAnimator canvasRotateAnim = ValueAnimator.ofInt(mCanvasAngle, mCanvasAngle + 90, mCanvasAngle + 180); canvasRotateAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() { @Override public void onAnimationUpdate(ValueAnimator animation) { mCanvasAngle = (int) animation.getAnimatedValue(); } }); animList.add(canvasRotateAnim); ValueAnimator circleYAnim = ValueAnimator.ofFloat(mEntireLineLength, mEntireLineLength / 4, mEntireLineLength); circleYAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() { @Override public void onAnimationUpdate(ValueAnimator animation) { mCircleY = (float) animation.getAnimatedValue(); invalidate(); } }); animList.add(circleYAnim); AnimatorSet animationSet = new AnimatorSet(); animationSet.setDuration(mDuration); animationSet.playTogether(animList); animationSet.setInterpolator(new LinearInterpolator()); animationSet.addListener(new AnimatorListener() { @Override public void onAnimationEnd(Animator animation) { Log.d("@=>", "动画3结束"); if (mStatus == STATUS_LOADING) { mStep++; startLCAnim(); } } }); animationSet.start(); mAnimList.add(animationSet); } ... @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); switch (mStep % 4) { ... case 2: for (int i = 0; i < mColors.length; i++) { mPaint.setColor(mColors[i]); drawCRCC(canvas, mWidth / 2 - mEntireLineLength / 2.2f, mHeight / 2 + mCircleY, mPaint, mCanvasAngle + i * 90); } break; ... } } ... private void drawCRCC(Canvas canvas, float x, float y, @NonNull Paint paint, int rotate) { canvas.rotate(rotate, mWidth / 2, mHeight / 2); canvas.drawCircle(x, y, mCircleRadius, paint); canvas.rotate(-rotate, mWidth / 2, mHeight / 2); }
动画3做了两件事：
1、旋转Canvas
2、变化Circle的Y坐标，达到往里缩的效果
四、线条变化动画（Line Change）
/** * Animation4 * 动画4 * Line Change * 线条变化动画 */ private void startLCAnim() { ValueAnimator lineWidthAnim = ValueAnimator.ofFloat(mEntireLineLength, -mEntireLineLength); lineWidthAnim.setDuration(mDuration); lineWidthAnim.setInterpolator(new LinearInterpolator()); lineWidthAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() { @Override public void onAnimationUpdate(ValueAnimator animation) { mLineLength = (float) animation.getAnimatedValue(); invalidate(); } }); lineWidthAnim.addListener(new AnimatorListener() { @Override public void onAnimationEnd(Animator animation) { Log.d("@=>", "动画4结束"); if (mStatus == STATUS_LOADING) { mStep++; startCRLCAnim(); } } }); lineWidthAnim.start(); mAnimList.add(lineWidthAnim); } ... @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); switch (mStep % 4) { ... case 3: for (int i = 0; i < mColors.length; i++) { mPaint.setColor(mColors[i]); drawLC(canvas, mWidth / 2 - mEntireLineLength / 2.2f, mHeight / 2 + mEntireLineLength, mWidth / 2 - mEntireLineLength / 2.2f, mHeight / 2 + mLineLength, mPaint, mCanvasAngle + i * 90); } break; } } ... private void drawLC(Canvas canvas, float startX, float startY, float stopX, float stopY, @NonNull Paint paint, int rotate) { canvas.rotate(rotate, mWidth / 2, mHeight / 2); canvas.drawArc(new RectF(startX - mCircleRadius, startY - mCircleRadius, startX + mCircleRadius, startY + mCircleRadius), 0, 180, true, mPaint); canvas.drawLine(startX, startY, stopX, stopY, paint); canvas.drawArc(new RectF(stopX - mCircleRadius, stopY - mCircleRadius, stopX + mCircleRadius, stopY + mCircleRadius), 180, 180, true, mPaint); canvas.rotate(-rotate, mWidth / 2, mHeight / 2); }
动画4只做了线条的变化。
这样整个Slack的Loading动画就完成了，是不是很简单。
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持脚本之家。