[移动开发]RecycleView自定义LayoutManager实现Gallery效果，2021Android最新大厂面试真题

前三个条目的位置和索引一样不用变,中间的为childCount-1,倒数第二个的绘图顺序是center,倒数第二个的绘图顺序是center+1,倒数第三个的绘图顺序是center+2,所以后三个对应的为center + childCount- 1 - i

public?class?GalleryRecycleview?extends?RecyclerView?{????public?GalleryRecycleview(Context?context)?{????????this(context,null);????}????public?GalleryRecycleview(Context?context,?@Nullable?AttributeSet?attrs)?{????????super(context,?attrs);????????setChildrenDrawingOrderEnabled(true);????}????@Override????protected?int?getChildDrawingOrder(int?childCount,?int?i)?{????????int?center?=?getlayoutManager().getCenterPos()????????????????-?getlayoutManager().getFistvisiblePos();?//计算正在显示的所有Item的中间位置????????int?order;????????if?(i?==?center)?{????????????order?=?childCount?-?1;????????}?else?if?(i?>?center)?{????????????order?=?center?+?childCount?-?1?-?i;????????}?else?{????????????order?=?i;????????}????????return?order;????}

在layoutmanager中获取第一个可见item和中间item的位置

public?int?getCenterPos()?{????????int?pos?=?(mTotalMoveX?/?getItemShowWidth());????????int?more?=?(mTotalMoveX?%?getItemShowWidth());????????if?(more?>?getItemShowWidth()?*?0.5f)?pos++;????????return?pos;????}????public?int?getFistvisiblePos()?{????????if(getItemCount()==0){????????????return?0;????????}????????return?getPosition(getChildAt(0));????}

可以看到已经是最后才绘制中间的item了

3、接着我们在layoutChild的时候加上动画

private?void?handleChildView(View?child,?int?moveX)?{????????float?radio?=?computeScale(moveX);????????float?rotation?=?computeRotationY(moveX);????????child.setScaleX(radio);????????child.setScaleY(radio);????????child.setRotationY(rotation);????}????private?float?computeScale(int?x)?{????????float?scale?=?1?-?Math.abs(x?*?1.0f?/?(6f?*?getItemShowWidth()));????????if?(scale?<?0)?scale?=?0;????????if?(scale?>?1)?scale?=?1;????????return?scale;????}????/**?????*?最大Y轴旋转度数?????*/????private?float?M_MAX_ROTATION_Y?=?30.0f;????private?float?computeRotationY(int?x)?{????????float?rotationY;????????rotationY?=?-M_MAX_ROTATION_Y?*?x?/?getItemShowWidth();????????if?(Math.abs(rotationY)?>?M_MAX_ROTATION_Y)?{????????????if?(rotationY?>?0)?{????????????????rotationY?=?M_MAX_ROTATION_Y;????????????}?else?{????????????????rotationY?=?-M_MAX_ROTATION_Y;????????????}????????}????????return?rotationY;????}

就和最上面的效果一样了

源码地址：
https://github.com/digtal/recycleview-study

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