RecyclerView的Item陰影效果

要為RecyclerView的Item添加陰影效果，可以通過以下步驟實現：

1. 創建一個自定義的ItemDecoration類，繼承自RecyclerView.ItemDecoration類。

public class ShadowItemDecoration extends RecyclerView.ItemDecoration {

    private int shadowSize;

    public ShadowItemDecoration(int shadowSize) {
        this.shadowSize = shadowSize;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        outRect.bottom = shadowSize;
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        for (int i = 0; i < parent.getChildCount(); i++) {
            View child = parent.getChildAt(i);
            drawShadow(c, child);
        }
    }

    private void drawShadow(Canvas canvas, View child) {
        Rect shadowRect = new Rect(child.getLeft(), child.getBottom(), child.getRight(), child.getBottom() + shadowSize);
        Paint paint = new Paint();
        paint.setColor(Color.GRAY);
        canvas.drawRect(shadowRect, paint);
    }
}

2. 在RecyclerView中設置ItemDecoration，并為每個Item添加陰影效果。

RecyclerView recyclerView = findViewById(R.id.recyclerView);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
recyclerView.addItemDecoration(new ShadowItemDecoration(20));
recyclerView.setAdapter(adapter);

通過以上步驟，你可以為RecyclerView的Item添加自定義的陰影效果。可以根據需求調整陰影的大小和顏色。