Android--自定义LayoutManager实现层叠卡片效果

public class CardLayoutManager extends RecyclerView.LayoutManager {
    @Override
    public RecyclerView.LayoutParams generateDefaultLayoutParams() {
        return new RecyclerView.LayoutParams(RecyclerView.LayoutParams.WRAP_CONTENT, RecyclerView.LayoutParams.WRAP_CONTENT);
    }

    /**
     * 自定义LayoutManager核心是摆放控件，所以onLayoutChildren方法是我们要改写的核心
     *
     * @param recycler
     * @param state
     */
    @Override
    public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
        //缓存
        detachAndScrapAttachedViews(recycler);

        //获取所有item(包括不可见的)个数
        int count = getItemCount();
        //由于我们是倒序摆放，所以初始索引从后面开始
        int initIndex = count - CardConfig.SHOW_MAX_COUNT;
        if (initIndex < 0) {
            initIndex = 0;
        }

        for (int i = initIndex; i < count; i++) {
            //从缓存中获取view
            View view = recycler.getViewForPosition(i);
            //添加到recyclerView
            addView(view);
            //测量一下view
            measureChild(view, 0, 0);

            //居中摆放，getDecoratedMeasuredWidth方法是获取带分割线的宽度，比直接使用view.getWidth()精确
            int realWidth = getDecoratedMeasuredWidth(view);
            int realHeight = getDecoratedMeasuredHeight(view);
            int widthPadding = (int) ((getWidth() - realWidth) / 2f);
            int heightPadding = (int) ((getHeight() - realHeight) / 2f);

            //摆放child
            layoutDecorated(view, widthPadding, heightPadding,
                    widthPadding + realWidth, heightPadding + realHeight);
            //根据索引，来位移和缩放child
            int level = count - i - 1;
            //level范围（CardConfig.SHOW_MAX_COUNT-1）- 0
            // 最下层的不动和最后第二层重叠
            if (level == CardConfig.SHOW_MAX_COUNT - 1) {
                level--;
            }
            view.setTranslationY(level * CardConfig.TRANSLATION_Y);
            view.setScaleX(1 - level * CardConfig.SCALE);
            view.setScaleY(1 - level * CardConfig.SCALE);
        }
    }
}

public class ItemTouchHelperCallback extends ItemTouchHelper.Callback {

    private List<String> mDatas;
    private RecyclerView.Adapter mAdapter;

    public ItemTouchHelperCallback(List<String> mDatas, RecyclerView.Adapter mAdapter) {
        this.mDatas = mDatas;
        this.mAdapter = mAdapter;
    }

    @Override
    public int getMovementFlags(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder) {

        return makeMovementFlags(0, ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT | ItemTouchHelper.UP | ItemTouchHelper.DOWN);
    }

    @Override
    public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ViewHolder viewHolder1) {
        return false;
    }

    @Override
    public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int i) {
        String s = mDatas.remove(viewHolder.getLayoutPosition());
        mDatas.add(0, s);
        mAdapter.notifyDataSetChanged();
    }

    @Override
    public void onChildDraw(@NonNull Canvas c, @NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
        //计算移动距离
        float distance = (float) Math.hypot(dX, dY);
        float maxDistance = recyclerView.getWidth() / 2f;

        //比例
        float fraction = distance / maxDistance;
        if (fraction > 1) {
            fraction = 1;
        }
        //为每个child执行动画
        int count = recyclerView.getChildCount();

        for (int i = 0; i < count; i++) {
            //获取的view从下层到上层
            View view = recyclerView.getChildAt(i);

            int level = CardConfig.SHOW_MAX_COUNT - i - 1;
            //level范围（CardConfig.SHOW_MAX_COUNT-1）-0，每个child最大只移动一个CardConfig.TRANSLATION_Y和放大CardConfig.SCALE

            if (level == CardConfig.SHOW_MAX_COUNT - 1) { // 最下层的不动和最后第二层重叠
                view.setTranslationY(CardConfig.TRANSLATION_Y * (level - 1));
                view.setScaleX(1 - CardConfig.SCALE * (level - 1));
                view.setScaleY(1 - CardConfig.SCALE * (level - 1));
            } else if (level > 0) {
                view.setTranslationY(level * CardConfig.TRANSLATION_Y - fraction * CardConfig.TRANSLATION_Y);
                view.setScaleX(1 - level * CardConfig.SCALE + fraction * CardConfig.SCALE);
                view.setScaleY(1 - level * CardConfig.SCALE + fraction * CardConfig.SCALE);
            }
        }

        super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
    }

    @Override
    public float getSwipeThreshold(@NonNull RecyclerView.ViewHolder viewHolder) {
        return 0.3f;
    }
}

public class MainActivity extends AppCompatActivity {
    RecyclerView rv;
    List<String> mStrings = new ArrayList<>();
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        rv = (RecyclerView) findViewById(R.id.rv);
        rv.setLayoutManager(new CardLayoutManager());
        
        for (int i = 1; i < 21; i++) {
            mStrings.add(String.valueOf(i));
        }
        MyAdapter myAdapter = new MyAdapter(this, mStrings);
        rv.setAdapter(myAdapter);

        ItemTouchHelperCallback itemTouchHelperCallback = new ItemTouchHelperCallback(mStrings, myAdapter);
        ItemTouchHelper itemTouchHelper = new ItemTouchHelper(itemTouchHelperCallback);
        itemTouchHelper.attachToRecyclerView(rv);
    }

    class MyAdapter extends RecyclerView.Adapter {
        private Context mContext;
        private List<String> mStrings;

        public MyAdapter(Context mContext, List<String> mStrings) {
            this.mContext = mContext;
            this.mStrings = mStrings;
        }

        @NonNull
        @Override
        public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
            return new MyViewHolder(LayoutInflater.from(mContext).inflate(R.layout.item_recyclerview, viewGroup, false));
        }

        @Override
        public void onBindViewHolder(@NonNull RecyclerView.ViewHolder viewHolder, int i) {
            MyViewHolder myViewHolder = (MyViewHolder) viewHolder;
            myViewHolder.textView.setText(mStrings.get(i) + "/" + getItemCount());
        }

        @Override
        public int getItemCount() {
            return mStrings.size();
        }

        class MyViewHolder extends RecyclerView.ViewHolder {
            public TextView textView;

            public MyViewHolder(@NonNull View itemView) {
                super(itemView);
                textView = itemView.findViewById(R.id.tv);
            }
        }
    }
}