RecyclerView边缘渐隐

可以通过设置RecyclerView的ItemDecoration来实现边缘渐隐效果。具体实现步骤如下：

1. 自定义一个继承自RecyclerView.ItemDecoration的类，重写其中的getItemOffsets()和onDraw()方法。

2. 在getItemOffsets()方法中，根据item的位置设置不同方向的偏移量，以便在onDraw()方法中绘制出边缘渐隐的效果。

3. 在onDraw()方法中，根据item的位置和偏移量绘制出边缘渐隐的效果。

以下是一个简单的示例代码：

public class EdgeFadeItemDecoration extends RecyclerView.ItemDecoration {
    private static final int DEFAULT_FADE_SIZE = 32; // 默认渐隐大小
    private int mFadeSize; // 渐隐大小

    public EdgeFadeItemDecoration() {
        this(DEFAULT_FADE_SIZE);
    }

    public EdgeFadeItemDecoration(int fadeSize) {
        mFadeSize = fadeSize;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        int position = parent.getChildAdapterPosition(view);
        int itemCount = parent.getAdapter().getItemCount();
        if (position == 0) { // 第一个item
            outRect.set(0, mFadeSize, 0, 0);
        } else if (position == itemCount - 1) { // 最后一个item
            outRect.set(0, 0, 0, mFadeSize);
        } else { // 中间的item
            outRect.set(0, 0, 0, 0);
        }
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        int childCount = parent.getChildCount();
        int itemCount = parent.getAdapter().getItemCount();
        int left = parent.getPaddingLeft();
        int right = parent.getWidth() - parent.getPaddingRight();
        for (int i = 0; i < childCount; i++) {
            View child = parent.getChildAt(i);
            int position = parent.getChildAdapterPosition(child);
            if (position == 0) { // 第一个item
                int top = child.getTop() - mFadeSize;
                int bottom = child.getTop();
                drawFade(c, left, top, right, bottom);
            } else if (position == itemCount - 1) { // 最后一个item
                int top = child.getBottom();
                int bottom = child.getBottom() + mFadeSize;
                drawFade(c, left, top, right, bottom);
            }
        }
    }

    private void drawFade(Canvas c, int left, int top, int right, int bottom) {
        GradientDrawable gradientDrawable = new GradientDrawable(GradientDrawable.Orientation.TOP_BOTTOM,
                new int[]{Color.TRANSPARENT, Color.BLACK});
        gradientDrawable.setBounds(left, top, right, bottom);
        gradientDrawable.draw(c);
    }
}