ViewGroup.TouchTarget

作为一个菜鸟，从今天开始记录2020年的源码阅读，希望能慢慢进步

TouchTarget是ViewGroup中的一个静态内部类，本次记录基于android-28的源码。

从注释看，应该是记录触碰的视图的一系列事件

源码如下

    private static final class TouchTarget {
        //链表最大长度
        private static final int MAX_RECYCLED = 32;
        //锁
        private static final Object sRecycleLock = new Object[0];
        private static TouchTarget sRecycleBin;
        private static int sRecycledCount;

        public static final int ALL_POINTER_IDS = -1; // all ones

        // The touched child view.
        public View child;

        // The combined bit mask of pointer ids for all pointers captured by the target.
        public int pointerIdBits;

        // The next target in the target list.
        public TouchTarget next;

        private TouchTarget() {
        }

       //获取链表头的TouchTarget
        public static TouchTarget obtain(@NonNull View child, int pointerIdBits) {
            if (child == null) {
                throw new IllegalArgumentException("child must be non-null");
            }

            final TouchTarget target;
            synchronized (sRecycleLock) {
             //没有链表头，则new一个TouchTarget返回
                if (sRecycleBin == null) {
                    target = new TouchTarget();
                } else {//否则 返回链表头
                    target = sRecycleBin;
                    //链表头指向下一个
                    sRecycleBin = target.next;
                   //长度-1
                     sRecycledCount--;
                    target.next = null;
                }
            }
            target.child = child;
            target.pointerIdBits = pointerIdBits;
            return target;
        }
       //通过头插法将该节点作为表头，原来的表头作为后继

        public void recycle() {
            if (child == null) {
                throw new IllegalStateException("already recycled once");
            }

            synchronized (sRecycleLock) {
                if (sRecycledCount < MAX_RECYCLED) {
                    next = sRecycleBin;
                    sRecycleBin = this;
                    sRecycledCount += 1;
                } else {
                    next = null;
                }
                child = null;
            }
        }
    }

1578036856(1).jpg

如图，obtain方法就是获取sRecycleBin指向的TouchTarget（next置为null），sRecycleBin指向next的对象（sRecycleBin不为null时）

recycle则是将当前的TouchTarget作为sRecycleBin插到头部