ViewGroup篇：玩一下自定义ViewGroup

自定义ViewGroup可不像自定义View那么简单

今日聚焦:

1.自定义ViewGroup中花样布局子View
2.移动View用layout、translation、TranslationAnimation、ViewPropertyAnimator、scrollTo、scrollBy有什么区别?
3.ViewGroup里怎么给孩子加动画
4.惯性移动? 也许你可以了解一下

效果 1	效果 2

一、前置知识:

1.生命函数

这是我曾经测试画出的一张图,描述了ViewGroup+两个孩子的生命函数调用情况

在这补充一点，ViewGroup在没有背景时不会走onDraw方法，但可以走dispatchDraw
原因在于View对onDraw的控制时做了限定：[if (!dirtyOpaque) onDraw(canvas)]  
你可以使用onDraw，在之前设个透明色即可:setBackgroundColor(0x00000000);

---

2.View与Activity之间

貌似一直没有对Activity与View的生命周期一起做过测试
测试之后发现View加载完成之后(onFinishInflate)并未立即回调测量、布局、绘制
而是在onResume之后View才会回调onAttachedToWindow-->onMeasure-->onSizeChanged-->onLayout-->onDraw
这一点确实让我挺惊讶，以前竟然没注意，现在理清了，通畅很多

2019-02-19 16:50:29.998 : onCreate --------------
2019-02-19 16:50:29.992 : 构造函数: 0
2019-02-19 16:50:29.996 : onFinishInflate: 0
2019-02-19 16:50:33.001 : onStart: ...................
2019-02-19 16:50:33.006 : onResume: ...................
2019-02-19 16:50:33.050 : onAttachedToWindow: 
2019-02-19 16:50:33.207 : onMeasure: 0
2019-02-19 16:50:33.243 : onMeasure: 0
2019-02-19 16:50:33.354 : onSizeChanged: 1948
2019-02-19 16:50:33.358 : onLayout: 1948
2019-02-19 16:50:33.395 : onDraw: 1948

---

二、自定义ViewGroup (排兵布阵)

经测试发现注意点:

[1].必须onMeasure中测量孩子的尺寸，否则无法显示
[2].必须onLayout中布局孩子的位置，否则无法显示
[3].在onLayout中孩子不能用view.getHeight()获取尺寸(因为为0)，只能用view.getMeasuredHeight

1.最简形式的ViewGroup

这里使用适配器模式，跟ListView一个套路,其实是非常简单，看箭头所指
这里暂时不对ViewGroup进行测量，先填满。对子View用自带的测量方法measureChildren

public class FlowerLayout extends ViewGroup {
    private int mRadius;
    private static final String TAG = "FlowerLayout";
--->private ListAdapter mAdapter;
--->public void setAdapter(ListAdapter adapter) {
        mAdapter = adapter;
    }
    public FlowerLayout(Context context) {
        this(context, null);
    }
    public FlowerLayout(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }
    public FlowerLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(attrs);
        setBackgroundColor(0x55D3E8FD);
    }
    private void init(AttributeSet attrs) {
    }
    private void formFlower() {
        for (int i = 0; i < mAdapter.getCount(); i++) {
    --->    View petal = mAdapter.getView(i, null, this);
            addView(petal);//填入花瓣
        }
    }
    @Override
    protected void onAttachedToWindow() {
        Log.e(TAG, "onAttachedToWindow: ");
--->    if (mAdapter != null) {
            formFlower();
        }
        super.onAttachedToWindow();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        measureChildren(widthMeasureSpec, heightMeasureSpec);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        //TODO 布局子view
    }
}

---->[Activity中使用]----------------
setContentView(R.layout.activity_flower);
FlowerLayout flowerLayout = findViewById(R.id.id_fl);
ArrayList<Petal> petals = new ArrayList<>();
petals.add(new Petal(R.mipmap.icon_1, "icon_1"));
petals.add(new Petal(R.mipmap.icon_2, "icon_2"));
petals.add(new Petal(R.mipmap.icon_3, "icon_3"));
petals.add(new Petal(R.mipmap.icon_4, "icon_4"));
petals.add(new Petal(R.mipmap.icon_5, "icon_5"));
petals.add(new Petal(R.mipmap.icon_6, "icon_6"));
petals.add(new Petal(R.mipmap.icon_7, "icon_7"));
petals.add(new Petal(R.mipmap.icon_8, "icon_8"));
petals.add(new Petal(R.mipmap.icon_9, "icon_9"));
petals.add(new Petal(R.mipmap.icon_10, "icon_10"));
flowerLayout.setAdapter(new FlowerAdapter(petals));

---->[FlowerAdapter视图适配器]---------------------------
public class FlowerAdapter extends BaseAdapter {
    private List<Petal> mPetals;
    public FlowerAdapter(List<Petal> petals) {
        mPetals = petals;
    }
    @Override
    public int getCount() {
        return mPetals.size();
    }
    @Override
    public Object getItem(int position) {
        return mPetals.get(position);
    }
    @Override
    public long getItemId(int position) {
        return position;
    }
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        LayoutInflater inflater = LayoutInflater.from(parent.getContext());
        View view = inflater.inflate(R.layout.flower_item, parent, false);
        ImageView iv = view.findViewById(R.id.id_pic);
        iv.setImageResource(mPetals.get(position).resId);
        TextView tv = view.findViewById(R.id.id_info);
        tv.setText(mPetals.get(position).info);
        return view;
    }
}

---

2.布局子view

这里关键在排布这里给张图先：子View布局的左上右下

---->[FlowerLayout#onLayout]----------------
 int childCount = getChildCount();
 for (int i = 0; i < childCount; i++) {
     View childView = getChildAt(i);
     int childW = childView.getMeasuredWidth();
     int childH = childView.getMeasuredHeight();
     int topPos = (int) (childH * i*0.5f);
     int leftPos = 0;
     childView.layout(leftPos, topPos, leftPos + childW, topPos + childH);
 }
 
 |-- 现在只要修改topPos和leftPos就可以改变子View布局

---

3.放置成圆形

---->[FlowerLayout#onLayout]----------------
int count = mAdapter.getCount();
for (int i = 0; i < count; i++) {
    View childView = getChildAt(i);
    int childW = childView.getMeasuredWidth();
    int childH = childView.getMeasuredHeight();
    mRadius = (getWidth()-childW) / 2;
    float posX = childW / 2 + mRadius - mRadius * cos(i * 360.f / count);
    float posY = childH / 2 + mRadius - mRadius * sin(i * 360.f / count);
    int leftPos = (int) (posX - childW / 2);
    int topPos = (int) (posY - childH / 2);
    childView.layout(leftPos, topPos, leftPos + childW, topPos + childH);
}

private float cos(float θ) {
    return (float) Math.cos(θ / 180 * Math.PI);
}
private float sin(float θ) {
    return (float) Math.sin(θ / 180 * Math.PI);
}

---

4.添加点击事件

这就比较容易了，一个监听搞定

//在形成View之后就添加点击事件
private void formFlower() {
   for (int i = 0; i < mAdapter.getCount(); i++) {
       View petal = mAdapter.getView(i, null, this);
       int position = i;
       if (mOnItemClickListener != null) {
           petal.setOnClickListener(v -> {
              ObjectAnimator.ofFloat(v, "ScaleX", 1f, 0.8f,1f).setDuration(200).start();
               ObjectAnimator.ofFloat(v, "ScaleY", 1f, 0.8f,1f).setDuration(200).start();
               mOnItemClickListener.onClick(v, this, position);
           });
       }
       addView(petal);//填入花瓣
   }


//----------------------------条目点击监听-------------------
public interface OnItemClickListener {
    void onClick(View v, ViewGroup viewGroup, int position);
}
private OnItemClickListener mOnItemClickListener;
public void setOnItemClickListener(OnItemClickListener onItemClickListener) {
    mOnItemClickListener = onItemClickListener;
}

5.数组点阵定位

这突然让我想到一个好玩的东西，那就是点阵控位。
点阵控位可以使用二维数组，也可以使用字符串，也可以使用像素点。
具体的可以详见我的这篇:这里就放一张核心的分析图：我们这里不画圆，而是取点位

/**
 * 用来显示点阵的二维数组
 */
public static final int[][] digit_test = new int[][]
        {
                {0, 0, 0, 1, 0, 0, 0},
                {0, 0, 1, 0, 1, 0, 0},
                {0, 0, 1, 0, 1, 0, 0},
                {0, 1, 0, 1, 0, 1, 0},
                {0, 1, 0, 0, 0, 1, 0},
                {0, 1, 0, 0, 0, 1, 0},
                {0, 0, 0, 0, 0, 0, 0},
                {0, 0, 0, 0, 0, 0, 0},
        };
        
/**
 * 点位解析器
 * @param w 单体宽
 * @param h 单体高
 * @return 解析成的点位数组
 */
private List<Point> renderDigit(int w, int h) {
    List<Point> points = new ArrayList<>();
    for (int i = 0; i < digit_test.length; i++) {
        for (int j = 0; j < digit_test[j].length; j++) {//一行一行遍历，遇到1就画
            if (digit_test[i][j] == 1) {
                int rX = (j * 2 + 1) * (w + 1);//第(i，j)个点圆心横坐标
                int rY = (i * 2 + 1) * (h + 1);//第(i，j)个点圆心纵坐标
                points.add(new Point(rX, rY));
            }
        }
    }
    return points;
}

---->[onLayout使用点位]-------------------
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
    List<Point> points = renderDigit(
            getChildAt(0).getMeasuredWidth() / 2,
            getChildAt(0).getMeasuredHeight() / 2
    );
    int count = mAdapter.getCount();
    for (int i = 0; i < count; i++) {
        View childView = getChildAt(i);
        int childW = childView.getMeasuredWidth();
        int childH = childView.getMeasuredHeight();
        mRadius = (getWidth() - childW) / 2;
        int leftPos = (int) (points.get(i).x - childW / 2);
        int topPos = (int) (points.get(i).y - childH / 2);
        childView.layout(leftPos, topPos, leftPos + childW, topPos + childH);
    }
}

ok了，只要把1放在你想要的位置，子View就在那里，
不过简单一点的还好说，要是爱心...来看神技:

---

5.位图点阵定位

用黑白(就相当于上面1,0)来标识点位，再根据Bitmap的像素进行
Bitmap内存杀手? 7*7像素的Bitmap也就九牛一毛...
就是下面的小不点，你可以下载玩玩。有PS，你也可以用ps自己戳点

---

---

mBitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.heart);

/**
 * 点位解析器
 *
 * @param bitmap bitmap
 * @param w 单体宽
 * @param h 单体高
 * @return 解析成的点位数组
 */
public static List<Point> renderBitmap(Bitmap bitmap, int w, int h) {
    List<Point> points = new ArrayList<>();
    for (int i = 0; i < bitmap.getWidth(); i++) {
        for (int j = 0; j < bitmap.getHeight(); j++) {
            int pixel = bitmap.getPixel(i, j);
            if (pixel != -1) {//此处过滤掉白颜色
                int rX = (i * 2 + 1) * (w + 1);//第(i，j)个点圆心横坐标
                int rY = (j * 2 + 1) * (h + 1);//第(i，j)个点圆心纵坐标
                points.add(new Point(rX, rY));
            }
        }
    }
    return points;
}

到这里排兵布阵就结束了,相信对onLayout已经能玩的6了吧，接下来上阵杀敌。

---

二.移动测试篇

既然是测试，就一切从简，直切问题本身，这里新建了一个Activity
并且打开了手机自带的布局便界显示，这样更能说明问题所在

1.布局

自定义：TestViewGroup+TestView纯原生，不加防腐剂
为了说明问题，这里的TestViewGroup加了边距20dp

<?xml version="1.0" encoding="utf-8"?>
<com.toly1994.analyzer.widget.TestViewGroup
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/fl"
    android:layout_marginTop="20dp"
    android:layout_marginStart="20dp"
    android:layout_width="300dp"
    android:layout_height="200dp"
    android:background="#5597FFFA">
    <com.toly1994.analyzer.widget.TestView
        android:id="@+id/view"
        android:layout_width="200dp"
        android:layout_height="50dp"
        android:background="#23F627"/>
</com.toly1994.analyzer.widget.TestViewGroup>

---

2.代码实现

/**
 * 作者：张风捷特烈<br/>
 * 时间：2019/2/20/020:10:30<br/>
 * 邮箱：1981462002@qq.com<br/>
 * 说明：测试ViewGroup
 */
public class TestViewGroup extends ViewGroup {
    public TestViewGroup(Context context) {
        super(context);
    }
    public TestViewGroup(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        measureChildren(widthMeasureSpec, heightMeasureSpec);
    }
    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        View child = getChildAt(0);
        child.layout(0, 0, child.getMeasuredWidth(), child.getMeasuredHeight());
    }
}

/**
 * 作者：张风捷特烈<br/>
 * 时间：2019/2/20/020:10:30<br/>
 * 邮箱：1981462002@qq.com<br/>
 * 说明：测试View
 */
public class TestView extends View {
    public TestView(Context context) {
        super(context);
    }
    public TestView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }
}

---

3.移动：layout与translation

这样对比应该非常明显：layout真的把布局移动了，translation只是离家出走而已

layout-----	translation
点击事件在绿色上	点击事件在绿色上

---->[TestViewGroup#onTouchEvent]-------------
@Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                int x = (int) event.getX();
                int y = (int) event.getY();
//                useLayout(mChild, x, y);
                useTranslation(mChild, x, y);
        }
        return super.onTouchEvent(event);
    }

    private void useLayout(View view, int x, int y) {
        view.layout(x, y,
                x + view.getMeasuredWidth(), y + view.getMeasuredHeight());
        //以下四行等价上一行
//                mChild.setLeft(x);
//                mChild.setTop(y);
//                mChild.setRight(x + mChild.getMeasuredWidth());
//                mChild.setBottom(y + mChild.getMeasuredHeight());
    }

    private void useTranslation(View view, int x, int y) {
        view.setTranslationX(x);
        view.setTranslationY(y);
    }

---

4 : 移动动画和属性动画

移动动画都是从家里开始，属性动画移动从当前位置，但是家还在那里!
也就是传说中的属性动画也并无法改变View的布局位置

TranslationAnimation	ViewPropertyAnimator
点击事件在家里	点击事件在绿色上

private void useTranslationAnimation(View view, int x, int y) {
    TranslateAnimation translateAnimation = new TranslateAnimation(0, x, 0, y);
    translateAnimation.setDuration(500);
    translateAnimation.setFillAfter(true);
    view.startAnimation(translateAnimation);
}

private void useViewPropertyAnimator(View view, int x, int y) {
    view.animate().translationX(x).translationY(y).setDuration(500).start();
    //下两句效果同上
//       ObjectAnimator.ofFloat(view, "translationX", x).setDuration(500).start();
//       ObjectAnimator.ofFloat(view, "translationY", y).setDuration(500).start();
}

---

5:哥就像让View搬家动画怎么办?

很简单：ValueAnimator呗，在刷新时对layout进行更新
由于有四个setXXX方法，这里，简单一点，使用ObjectAnimator

private void useLayoutAnimate(View view, int x, int y) {
    //下两句效果同上
    ObjectAnimator.ofInt(view, "Left", x).setDuration(500).start();
    ObjectAnimator.ofInt(view, "Top", y).setDuration(500).start();
    ObjectAnimator.ofInt(view, "Right", x+view.getMeasuredWidth()).setDuration(500).start();
    ObjectAnimator.ofInt(view, "Bottom", y + view.getMeasuredHeight()).setDuration(500).start();
}

---

6:scrollTo和scrollBy

可以说这两个方法和上面的不是一辈的人，应用场景有很大区别
这两个方法是移动一个View内部的所有子View,调用方并非子View
至于To和By的区别，也是老生常谈，看图体悟吧...

scrollTo	scrollBy

---->[onTouchEvent]---------------
useScrollTo(-x, -y);
useScrollBy(-x, -y);

--------------------------------------------
private void useScrollTo(int x, int y) {
    scrollTo(x, y);
}
private void useScrollBy(int x, int y) {
    scrollBy(x, y);
}

Ok ,基础知识就到这里，言归正传：

---

三、添加动画

下面这幅图应该不难吧，如果做不出来...下面的就当看风景吧...

静态	动态

---

1.首先把排成圆的方法封装一下

/**
 * @param start 第一个排成圆的View索引
 * @param dθ    旋转角度
 */
private void layoutCircle(int start, float dθ) {
    int count = getChildCount();
    for (int i = start; i < count; i++) {
        View childView = getChildAt(i);
        int childW = childView.getMeasuredWidth();
        int childH = childView.getMeasuredHeight();
        int r = (getWidth() - childW) / 2;
        float posX = childW / 2 + r - r * cos(i * 360.f / (count - 1) + dθ);
        float posY = childH / 2 + r - r * sin(i * 360.f / (count - 1) + dθ);
        int leftPos = (int) (posX - childW / 2);
        int topPos = (int) (posY - childH / 2);
        childView.layout(leftPos, topPos, leftPos + childW, topPos + childH);
    }
}

---

2.ValueAnimator走起

在点击的时候触发mAnimator.start()即可

mAnimator = ValueAnimator.ofInt(0, 360);
mAnimator.setDuration(3000);
mAnimator.addUpdateListener(a -> {
    int deg = (int) a.getAnimatedValue();
    layoutCircle(1, deg);
});

---

3.位置交换的功能

这里实现和中心的交换，并且加入移动动画

无动画	有动画

---->[维护成员变量]-------------
private int centerId = 0;//默认中心点

/**
 * 交换两个View的位置
 * @param positionMe 点击者
 * @param positionHe 目标
 */
private void swap(int positionMe, int positionHe) {
    View me = getChildAt(positionMe);
    View he = getChildAt(positionHe);
    int TempMeLeft = me.getLeft();
    int TempMeTop = me.getTop();
    int TempMeRight = me.getRight();
    int TempMeBottom = me.getBottom();
    me.layout(he.getLeft(), he.getTop(), he.getRight(), he.getBottom());
    he.layout(TempMeLeft, TempMeTop, TempMeRight, TempMeBottom);
    centerId = positionMe;
}

|--然后只需要在需要的时候触发即可：
swap(position, centerId);

---

动画，刚才貌似写过了，直接拿来用

/**
 * 交换两个View的位置
 * @param positionMe 点击者
 * @param positionHe 目标 
 */
private void swapWithAnim(int positionMe, int positionHe) {
    View me = getChildAt(positionMe);
    View he = getChildAt(positionHe);
    int TempMeLeft = me.getLeft();
    int TempMeTop = me.getTop();
    useLayoutAnimate(me, he.getLeft(), he.getTop());
    useLayoutAnimate(he, TempMeLeft,TempMeTop);
    centerId = positionMe;
}
private void useLayoutAnimate(View view, int x, int y) {
    ObjectAnimator.ofInt(view, "Left", x).setDuration(500).start();
    ObjectAnimator.ofInt(view, "Top", y).setDuration(500).start();
    ObjectAnimator.ofInt(view, "Right", x + view.getMeasuredWidth()).setDuration(500).start();
    ObjectAnimator.ofInt(view, "Bottom", y + view.getMeasuredHeight()).setDuration(500).start();
}

既然可以动画，那么则么玩都可以，比如旋转和放大
动画就不展开了，详情可见：Android 动画 Animator 家族使用指南

旋转	放大

三、你觉得无聊，玩点6的

1.神技之一：VelocityTracker

这个类估计听过的人不多，翻译出来是速度追踪器，作为一个好用的类，在此拎出来讲一讲
它的作用是获取你滑动的x,y的速度x 左负，y上负

---->[FlowerLayout#init]---------------
private void init(AttributeSet attrs) {
    ...
    velocityTracker = VelocityTracker.obtain();//1.VelocityTracker的创建
}

---->[FlowerLayout#onTouchEvent]---------------
@Override
public boolean onTouchEvent(MotionEvent event) {
    View centerView = getChildAt(0);
    velocityTracker.addMovement(event);//2.VelocityTracker与event结合
    switch (event.getAction()) {
          case MotionEvent.ACTION_DOWN:
              ...
              break;
        case MotionEvent.ACTION_MOVE:
            velocityTracker.computeCurrentVelocity(1000);//3.计算速度
            //4.获取值
            Log.e(TAG, "X velocity: " + velocityTracker.getXVelocity()+
                    "--Y velocity: " + velocityTracker.getYVelocity());
            break;
        case MotionEvent.ACTION_UP:
              ...
            break;
    }
    return true;
}
|--注意第5点：在适当的地方取消和回收
velocityTracker.clear();//取消
velocityTracker.recycle();//回收

|---我们比较在意的是计算速度的方法，1000是搞嘛的?
/**
 * Equivalent to invoking {@link #computeCurrentVelocity(int, float)} with a maximum
 * velocity of Float.MAX_VALUE.
 * 也就是说这里的第三参是Float的最大值，表示这个速度足以超光速
 * @see #computeCurrentVelocity(int, float) 
 */
public void computeCurrentVelocity(int units) {
    nativeComputeCurrentVelocity(mPtr, units, Float.MAX_VALUE);
}

 /**
  * @param units The units you would like the velocity in.  A value of 1
  * provides pixels per millisecond, 1000 provides pixels per second, etc.
    你想要的单位是速度。值1表示像素/毫秒，1000表示像素/秒，等等。
  * @param maxVelocity The maximum velocity that can be computed by this method.
  * This value must be declared in the same unit as the units parameter. This value
  * must be positive. 该方法可以计算的最大值
  */
 public void computeCurrentVelocity(int units, float maxVelocity) {
     nativeComputeCurrentVelocity(mPtr, units, maxVelocity);
 }
 |-- native方法就不挖了

---

2.有了速度能干嘛?

注 接下来的这部分源于陈小缘的Android实现圆弧滑动效果之ArcSlidingHelper篇
我认真研究了一下，并融入了本ViewGroup，他封装的非常好，我拆了一下截取了和惯性相关的部分
不懂的可以去深度一下，我就不卖弄唇舌了，GitHub在：ArcSlidingHelper

---->[FlowerLayout#onLayout]--------------------
private void initRotate() {
    int width = getWidth();
    int height = getHeight();
    mPivotX = width/2;
    mPivotY = height/2;
    mVelocityTracker = VelocityTracker.obtain();
    mScrollAvailabilityRatio = .3F;
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    View centerView = getChildAt(0);
    float x, y;
    x = event.getRawX();
    y = event.getRawY();
    mVelocityTracker.addMovement(event);
    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            mAnimator.start();
            abortAnimation();
              centerView.layout(x, y,
                      x + centerView.getMeasuredWidth(), y + centerView.getMeasuredHeight());
            Log.e("EVENT", "onTouchEvent: " + x + "------" + y);
            break;
        case MotionEvent.ACTION_MOVE:
            handleActionMove(x, y);
            break;
        case MotionEvent.ACTION_UP:
        case MotionEvent.ACTION_CANCEL:
        case MotionEvent.ACTION_OUTSIDE:
            mVelocityTracker.computeCurrentVelocity(1000);
            mScroller.fling(0, 0,
                    (int) mVelocityTracker.getXVelocity(),
                    (int) mVelocityTracker.getYVelocity(),
                    Integer.MIN_VALUE, Integer.MAX_VALUE,
                    Integer.MIN_VALUE, Integer.MAX_VALUE);
            startFling();
            break;
    }
    mStartX = x;
    mStartY = y;
    return true;
}


//------------------------惯性旋转----------------------------
private Scroller mScroller = new Scroller(getContext());
private int mPivotX, mPivotY;
private float mStartX, mStartY;
private float mLastScrollOffset;
private float mScrollAvailabilityRatio;
private boolean isClockwiseScrolling;
private boolean isShouldBeGetY;
private boolean isRecycled;
private VelocityTracker mVelocityTracker;
private Handler mHandler = new Handler(msg -> {
    computeInertialSliding();
    return false;
});
/**
 * 处理惯性滚动
 */
private void computeInertialSliding() {
    checkIsRecycled();
    if (mScroller.computeScrollOffset()) {
        float y = ((isShouldBeGetY ? mScroller.getCurrY() : mScroller.getCurrX()) * mScrollAvailabilityRatio);
        if (mLastScrollOffset != 0) {
            float offset = fixAngle(Math.abs(y - mLastScrollOffset));
            float deg = isClockwiseScrolling ? offset : -offset;
            setRotation(getRotation() + deg);
        }
        mLastScrollOffset = y;
        startFling();
    } else if (mScroller.isFinished()) {
        mLastScrollOffset = 0;
    }
}
/**
 * 计算滑动的角度
 */
private void handleActionMove(float x, float y) {
    float l, t, r, b;
    if (mStartX > x) {
        r = mStartX;
        l = x;
    } else {
        r = x;
        l = mStartX;
    }
    if (mStartY > y) {
        b = mStartY;
        t = y;
    } else {
        b = y;
        t = mStartY;
    }
    float pA1 = Math.abs(mStartX - mPivotX);
    float pA2 = Math.abs(mStartY - mPivotY);
    float pB1 = Math.abs(x - mPivotX);
    float pB2 = Math.abs(y - mPivotY);
    float hypotenuse = (float) Math.sqrt(Math.pow(r - l, 2) + Math.pow(b - t, 2));
    float lineA = (float) Math.sqrt(Math.pow(pA1, 2) + Math.pow(pA2, 2));
    float lineB = (float) Math.sqrt(Math.pow(pB1, 2) + Math.pow(pB2, 2));
    if (hypotenuse > 0 && lineA > 0 && lineB > 0) {
        float angle = fixAngle((float) Math.toDegrees(Math.acos((Math.pow(lineA, 2) + Math.pow(lineB, 2) - Math.pow(hypotenuse, 2)) / (2 * lineA * lineB))));
        float deg = (isClockwiseScrolling = isClockwise(x, y)) ? angle : -angle;
        setRotation(getRotation() + deg);
    }
}
/**
 * 打断动画
 */
public void abortAnimation() {
    checkIsRecycled();
    if (!mScroller.isFinished()) {
        mScroller.abortAnimation();
    }
}
/**
 * 释放资源
 */
public void release() {
    checkIsRecycled();
    mScroller = null;
    mVelocityTracker.recycle();
    mVelocityTracker = null;
    isRecycled = true;
}
/**
 * 检测手指是否顺时针滑动
 *
 * @param x 当前手指的x坐标
 * @param y 当前手指的y坐标
 * @return 是否顺时针
 */
private boolean isClockwise(float x, float y) {
    return (isShouldBeGetY = Math.abs(y - mStartY) > Math.abs(x - mStartX)) ?
            x < mPivotX != y > mStartY : y < mPivotY == x > mStartX;
}
/**
 * 开始惯性滚动
 */
private void startFling() {
    mHandler.sendEmptyMessage(0);
}
/**
 * 调整角度，使其在360之间
 *
 * @param rotation 当前角度
 * @return 调整后的角度
 */
private float fixAngle(float rotation) {
    float angle = 360F;
    if (rotation < 0) {
        rotation += angle;
    }
    if (rotation > angle) {
        rotation = rotation % angle;
    }
    return rotation;
}
/**
 * 检查资源释放已经释放
 */
private void checkIsRecycled() {
    if (isRecycled) {
        throw new IllegalStateException(" is recycled!");
    }
}

OK，今天就到这里

---

后记：捷文规范

1.本文成长记录及勘误表

项目源码	日期	附录
V0.1--github	2018-2-20	无

发布名：View篇：玩一下自定义ViewGroup
捷文链接：juejin.cn/post/684490…

2.更多关于我

笔名	QQ	微信
张风捷特烈	1981462002	zdl1994328

我的github：github.com/toly1994328
我的简书：www.jianshu.com/u/e4e52c116…
我的掘金：juejin.cn/user/149189…
个人网站：www.toly1994.com

3.声明

1----本文由张风捷特烈原创,转载请注明
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