最近看到豆瓣的笑臉loading很有意思，看一張效果圖：

下面分析一下如何實現這樣的效果：

1、默認狀態是一張笑臉的狀態(一個嘴巴，兩個眼睛，默認狀態)

2、開始旋轉，嘴巴追上眼睛(合并狀態)

3、追上以后自轉一周(自轉狀態)

4、然后逐漸釋放眼睛(分離狀態)

5、回到初始笑臉狀態（默認狀態）

首先需要確定好嘴巴和眼睛的初始位置，我這里的初始化嘴巴是一個半圓，在橫軸下方。眼睛分別與橫軸夾角60度，如下圖：

這兩部分可以使用pathMeasure，我這里使用最簡單的兩個api：canvas.drawArc()和canvas.drawPoint()。

//畫起始笑臉canvas.drawArc(-radius, -radius, radius, radius, startAngle, swipeAngle, false,facePaint);

這里的startAngle初始值為0，swiperAngle為180，半徑radius為40。

（1）初始化眼睛坐標

/** * 初始化眼睛坐標 */ private void initEyes() {//默認兩個眼睛坐標位置 角度轉弧度leftEyeX = (float) (-radius * Math.cos(eyeStartAngle * Math.PI / 180));leftEyeY = (float) (-radius * Math.sin(eyeStartAngle * Math.PI / 180));rightEyeX = (float) (radius * Math.cos(eyeStartAngle * Math.PI / 180));rightEyeY = (float) (-radius * Math.sin(eyeStartAngle * Math.PI / 180)); }

注意：需要將角度轉弧度

（2）開始畫眼睛

//畫起始眼睛 canvas.drawPoint(leftEyeX, leftEyeY, eyePaint); canvas.drawPoint(rightEyeX, rightEyeY, eyePaint);二、合并狀態

這個狀態可以分為兩部分

開啟動畫

faceLoadingAnimator = ValueAnimator.ofFloat(0, 1).setDuration(1000); faceLoadingAnimator.setInterpolator(new AccelerateDecelerateInterpolator()); faceLoadingAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() { @Override public void onAnimationUpdate(ValueAnimator animation) {faceValue = (float) animation.getAnimatedValue();invalidate(); }});//動畫延遲500ms啟動faceLoadingAnimator.setStartDelay(200);faceLoadingAnimator.addListener(new Animator.AnimatorListener() { @Override public void onAnimationStart(Animator animation) { } @Override public void onAnimationEnd(Animator animation) {//恢復起始狀態currentStatus = smileStatus; } @Override public void onAnimationCancel(Animator animation) { } @Override public void onAnimationRepeat(Animator animation) { }});

動畫執行時間1s，記錄動畫當前執行進度值，存放在faceValue中。當動畫執行結束的時候，需要將狀態恢復到默認狀態，調用invalidate的時候，進入onDraw()方法，開始重新繪制嘴巴。

//記錄時刻的旋轉角度startAngle = faceValue * 360;//追上右邊眼睛if (startAngle >= 120 + startAngle / 2) { canvas.drawArc(-radius, -radius, radius, radius, startAngle, swipeAngle, false, facePaint); //開始自轉一圈 mHandler.sendEmptyMessage(2); //此時記錄自轉一圈起始的角度 circleStartAngle = 120 + startAngle / 2;} else { //追眼睛的過程 canvas.drawArc(-radius, -radius, radius, radius, startAngle, swipeAngle, false, facePaint);}

這里的每次旋轉角度為startAngle。當完全追趕上右側眼睛的時候，開始執行自轉一周，并停止當前動畫。

眼睛的開始旋轉速度明顯是慢于嘴巴的旋轉速度，所以每次的旋轉速度可以設置為嘴巴的一半

//畫左邊眼睛 ，旋轉的角度設置為笑臉旋轉角度的一半，這樣笑臉才能追上眼睛 leftEyeX = (float) (-radius * Math.cos((60 + startAngle / 2) * Math.PI / 180)); leftEyeY = (float) (-radius * Math.sin((60 + startAngle / 2) * Math.PI / 180)); canvas.drawPoint(leftEyeX, leftEyeY, eyePaint); //畫右邊眼睛 ，旋轉的角度設置為笑臉旋轉角度的一半，這樣笑臉才能追上眼睛 rightEyeX = (float) (radius * Math.cos((60 - startAngle / 2) * Math.PI / 180)); rightEyeY = (float) (-radius * Math.sin((60 - startAngle / 2) * Math.PI / 180)); canvas.drawPoint(rightEyeX, rightEyeY, eyePaint);三、自轉狀態1、開啟動畫

circleAnimator = ValueAnimator.ofFloat(0, 1).setDuration(1000);circleAnimator.setInterpolator(new LinearInterpolator());circleAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() { @Override public void onAnimationUpdate(ValueAnimator animation) {circleValue = (float) animation.getAnimatedValue();invalidate(); }});circleAnimator.addListener(new Animator.AnimatorListener() { @Override public void onAnimationStart(Animator animation) { } @Override public void onAnimationEnd(Animator animation) {mHandler.sendEmptyMessage(3); } @Override public void onAnimationCancel(Animator animation) { } @Override public void onAnimationRepeat(Animator animation) { }});2、重新繪制

canvas.drawArc(-radius, -radius, radius, radius,circleStartAngle + circleValue * 360,swipeAngle, false, facePaint);四、分離狀態

主要的注意點就是眼睛的旋轉角度設置為嘴巴旋轉角度的2倍，這樣才會達到眼睛超過嘴巴的效果，主要的旋轉代碼如下：

startAngle = faceValue * 360;//判斷當前笑臉的起點是否已經走過260度 (吐出眼睛的角度，角度可以任意設置)if (startAngle >= splitAngle) { //畫左邊眼睛 ，旋轉的角度設置為笑臉旋轉角度的2倍，這樣眼睛才能快于笑臉旋轉速度 leftEyeX = (float) (-radius * Math.cos((eyeStartAngle + startAngle * 2) * Math.PI / 180)); leftEyeY = (float) (-radius * Math.sin((eyeStartAngle + startAngle * 2) * Math.PI / 180)); canvas.drawPoint(leftEyeX, leftEyeY, eyePaint); //畫右邊眼睛 ，旋轉的角度設置為笑臉旋轉角度的2倍，這樣眼睛才能快于笑臉旋轉速度 rightEyeX = (float) (radius * Math.cos((eyeStartAngle - startAngle * 2) * Math.PI / 180)); rightEyeY = (float) (-radius * Math.sin((eyeStartAngle - startAngle * 2) * Math.PI / 180)); canvas.drawPoint(rightEyeX, rightEyeY, eyePaint);}//畫笑臉canvas.drawArc(-radius, -radius, radius, radius, startAngle, swipeAngle,false, facePaint);最后附上完整代碼

public class FaceView2 extends View { //圓弧半徑 private int radius = 40; //圓弧畫筆寬度 private float paintWidth = 15; //笑臉狀態(一個臉，兩個眼睛) private final int smileStatus = 0; //加載狀態 合并眼睛，旋轉 private final int loadingStatus = 1; //合并完成 轉一圈 private final int circleStatus = 2; //轉圈完成 吐出眼睛 private final int splitStatus = 3; //當前狀態 private int currentStatus = smileStatus; //笑臉畫筆 private Paint facePaint; //眼睛畫筆 private Paint eyePaint; //笑臉開始角度 private float startAngle; //笑臉弧度 private float swipeAngle; //左側眼睛起點x軸坐標 private float leftEyeX = 0; //左側眼睛起點y軸坐標 private float leftEyeY = 0; //右側眼睛起點x軸坐標 private float rightEyeX; //右側眼睛起點y軸坐標 private float rightEyeY; //一開始默認狀態笑臉轉圈動畫 private ValueAnimator faceLoadingAnimator; //吞并完成后，自轉一圈動畫 private ValueAnimator circleAnimator; //faceLoadingAnimator動畫進度值 private float faceValue; //circleAnimator動畫進度值 private float circleValue; //記錄開始自轉一圈的起始角度 private float circleStartAngle; //吐出眼睛的角度 private float splitAngle; private float initStartAngle; //眼睛起始角度 private float eyeStartAngle = 60; public FaceView2(Context context) {this(context, null); } public FaceView2(Context context, AttributeSet attrs) {this(context, attrs, 0); } public FaceView2(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);//自定義屬性TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.FaceView2,defStyleAttr, 0);initStartAngle = typedArray.getFloat(R.styleable.FaceView2_startAngle, 0);swipeAngle = typedArray.getFloat(R.styleable.FaceView2_swipeAngle, 180);splitAngle = typedArray.getFloat(R.styleable.FaceView2_splitAngle, 260);typedArray.recycle();startAngle = initStartAngle;eyeStartAngle += startAngle;initEyes();initPaint();//開始默認動畫initAnimator(); } /** * 初始化畫筆 */ private void initPaint() {//初始化畫筆facePaint = new Paint();facePaint.setStrokeWidth(paintWidth);facePaint.setColor(Color.RED);facePaint.setAntiAlias(true);facePaint.setStyle(Paint.Style.STROKE);facePaint.setStrokeCap(Paint.Cap.ROUND);eyePaint = new Paint();eyePaint.setStrokeWidth(paintWidth);eyePaint.setColor(Color.RED);eyePaint.setAntiAlias(true);eyePaint.setStyle(Paint.Style.STROKE);eyePaint.setStrokeCap(Paint.Cap.ROUND); } /** * 初始化眼睛坐標 */ private void initEyes() {//默認兩個眼睛坐標位置 角度轉弧度leftEyeX = (float) (-radius * Math.cos(eyeStartAngle * Math.PI / 180));leftEyeY = (float) (-radius * Math.sin(eyeStartAngle * Math.PI / 180));rightEyeX = (float) (radius * Math.cos(eyeStartAngle * Math.PI / 180));rightEyeY = (float) (-radius * Math.sin(eyeStartAngle * Math.PI / 180)); } private Handler mHandler = new Handler(new Handler.Callback() {@RequiresApi(api = Build.VERSION_CODES.KITKAT)@Overridepublic boolean handleMessage(Message msg) { switch (msg.what) {case 1: //啟動一開始笑臉轉圈動畫，并且開始合并眼睛 currentStatus = loadingStatus; faceLoadingAnimator.start(); break;case 2: //暫停眼睛和笑臉動畫 currentStatus = circleStatus; faceLoadingAnimator.pause(); //啟動笑臉自轉一圈動畫 circleAnimator.start(); break;case 3: //恢復笑臉轉圈動畫，并且開始分離眼睛 currentStatus = splitStatus; circleAnimator.cancel(); faceLoadingAnimator.resume(); invalidate(); break; } return false;} }); @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP) @Override protected void onDraw(Canvas canvas) {super.onDraw(canvas);//畫布移到中間canvas.translate(getWidth() / 2, getHeight() / 2);switch (currentStatus) { //起始狀態 case smileStatus://起始角度為0startAngle = initStartAngle;//畫起始笑臉canvas.drawArc(-radius, -radius, radius, radius, startAngle, swipeAngle, false,facePaint);//重置起始眼睛坐標initEyes();//畫起始眼睛canvas.drawPoint(leftEyeX, leftEyeY, eyePaint);canvas.drawPoint(rightEyeX, rightEyeY, eyePaint);//更改狀態，進行笑臉合并眼睛mHandler.sendEmptyMessage(1);break; //合并狀態 case loadingStatus://記錄時刻的旋轉角度startAngle = faceValue * 360;//追上右邊眼睛if (startAngle >= 120 + startAngle / 2) { canvas.drawArc(-radius, -radius, radius, radius, startAngle, swipeAngle, false, facePaint); //開始自轉一圈 mHandler.sendEmptyMessage(2); //此時記錄自轉一圈起始的角度 circleStartAngle = 120 + startAngle / 2;} else { //追眼睛的過程 canvas.drawArc(-radius, -radius, radius, radius, startAngle, swipeAngle, false, facePaint);}//畫左邊眼睛 ，旋轉的角度設置為笑臉旋轉角度的一半，這樣笑臉才能追上眼睛leftEyeX = (float) (-radius * Math.cos((60 + startAngle / 2) * Math.PI / 180));leftEyeY = (float) (-radius * Math.sin((60 + startAngle / 2) * Math.PI / 180));canvas.drawPoint(leftEyeX, leftEyeY, eyePaint);//畫右邊眼睛 ，旋轉的角度設置為笑臉旋轉角度的一半，這樣笑臉才能追上眼睛rightEyeX = (float) (radius * Math.cos((60 - startAngle / 2) * Math.PI / 180));rightEyeY = (float) (-radius * Math.sin((60 - startAngle / 2) * Math.PI / 180));canvas.drawPoint(rightEyeX, rightEyeY, eyePaint);break; //自轉一圈狀態 circleValue * 360 為旋轉角度 case circleStatus:canvas.drawArc(-radius, -radius, radius, radius,circleStartAngle + circleValue * 360,swipeAngle, false, facePaint);break; //笑臉眼睛分離狀態 case splitStatus:startAngle = faceValue * 360;//判斷當前笑臉的起點是否已經走過260度 (吐出眼睛的角度，角度可以任意設置)if (startAngle >= splitAngle) { //畫左邊眼睛 ，旋轉的角度設置為笑臉旋轉角度的2倍，這樣眼睛才能快于笑臉旋轉速度 leftEyeX = (float) (-radius * Math.cos((eyeStartAngle + startAngle * 2) * Math.PI / 180)); leftEyeY = (float) (-radius * Math.sin((eyeStartAngle + startAngle * 2) * Math.PI / 180)); canvas.drawPoint(leftEyeX, leftEyeY, eyePaint); //畫右邊眼睛 ，旋轉的角度設置為笑臉旋轉角度的2倍，這樣眼睛才能快于笑臉旋轉速度 rightEyeX = (float) (radius * Math.cos((eyeStartAngle - startAngle * 2) * Math.PI / 180)); rightEyeY = (float) (-radius * Math.sin((eyeStartAngle - startAngle * 2) * Math.PI / 180)); canvas.drawPoint(rightEyeX, rightEyeY, eyePaint);}//畫笑臉canvas.drawArc(-radius, -radius, radius, radius, startAngle, swipeAngle,false, facePaint);break;} } /** * 初始化動畫 */ private void initAnimator() {faceLoadingAnimator = ValueAnimator.ofFloat(0, 1).setDuration(1000);faceLoadingAnimator.setInterpolator(new AccelerateDecelerateInterpolator());faceLoadingAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() { @Override public void onAnimationUpdate(ValueAnimator animation) {faceValue = (float) animation.getAnimatedValue();invalidate(); }});//動畫延遲500ms啟動faceLoadingAnimator.setStartDelay(200);faceLoadingAnimator.addListener(new Animator.AnimatorListener() { @Override public void onAnimationStart(Animator animation) { } @Override public void onAnimationEnd(Animator animation) {//恢復起始狀態currentStatus = smileStatus; } @Override public void onAnimationCancel(Animator animation) { } @Override public void onAnimationRepeat(Animator animation) { }});circleAnimator = ValueAnimator.ofFloat(0, 1).setDuration(1000);circleAnimator.setInterpolator(new LinearInterpolator());circleAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() { @Override public void onAnimationUpdate(ValueAnimator animation) {circleValue = (float) animation.getAnimatedValue();invalidate(); }});circleAnimator.addListener(new Animator.AnimatorListener() { @Override public void onAnimationStart(Animator animation) { } @Override public void onAnimationEnd(Animator animation) {mHandler.sendEmptyMessage(3); } @Override public void onAnimationCancel(Animator animation) { } @Override public void onAnimationRepeat(Animator animation) { }}); }}

自定義屬性

<declare-styleable name='FaceView2'><attr name='startAngle' format='dimension' /><attr name='swipeAngle' format='dimension' /><attr name='splitAngle' format='dimension' /></declare-styleable>

布局文件中使用

<com.example.viewdemo.FaceView2 android:layout_width='match_parent' android:layout_height='match_parent'/>

完整代碼都在上面啦.

到這里就結束啦.

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