RecyclerView之ItemDecoration在屏幕中增加下划线的一个小demo

本文展示了如何在Android的RecyclerView中使用ItemDecoration实现屏幕内添加下划线的效果。通过自定义GridItemDecorator，将屏幕分为三等份，并确保屏幕边缘无分割线。

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首先，在activity中：

localVideoRecycView.addItemDecoration(new GridItemDecorator(this));
localVideoRecycView.setLayoutManager(new GridLayoutManager(this, 3));

调用ItemDecoration方法

class GridItemDecorator extends RecyclerView.ItemDecoration {
    private final Drawable mDivider;

    public GridItemDecorator(Context context) {
        mDivider = context.getResources().getDrawable(R.drawable.dividing_line);
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDraw(c, parent, state);
        drawVertical(c, parent);
        drawHorizontal(c, parent);
    }

    // 绘制垂直方向分割线
    private void drawVertical(Canvas c, RecyclerView parent) {
        int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            View child = parent.getChildAt(i);
            RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
            int left = child.getRight() + params.rightMargin;
            int top = child.getTop() - params.topMargin;
            int right = left + mDivider.getIntrinsicWidth();
            int bottom = child.getBottom() + params.bottomMargin;
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }

    // 绘制水平方向分割线
    private void drawHorizontal(Canvas c, RecyclerView parent) {
        int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            View child = parent.getChildAt(i);
            RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
            int left = child.getLeft() - params.leftMargin;
            int top = child.getBottom() + params.bottomMargin;
            int right = child.getRight() + params.rightMargin;
            int bottom = top + mDivider.getMinimumHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }

    @Override
    public void getItemOffsets(Rect outRect, int itemPosition, RecyclerView parent) {
        super.getItemOffsets(outRect, itemPosition, parent);
        int right = mDivider.getIntrinsicWidth();
        int bottom = mDivider.getIntrinsicHeight();

        if (isLastSpan(itemPosition, parent)) {
            right = 0;
        }

        if (isLastRow(itemPosition, parent)) {
            bottom = 0;
        }
        outRect.set(0, 0, right, bottom);
    }

    // 判断是否是最后一行
    public boolean isLastRow(int itemPosition, RecyclerView parent) {
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager) {
            int spanCount = ((GridLayoutManager) layoutManager).getSpanCount();
            int itemCount = parent.getAdapter().getItemCount();
            if ((itemCount - itemPosition - 1) < spanCount) {
                return true;
            }
        }
        return false;
    }

    // 判断是否是最后一列
    public boolean isLastSpan(int itemPosition, RecyclerView parent) {
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager) {
            int spanCount = ((GridLayoutManager) layoutManager).getSpanCount();
            if ((itemPosition + 1) % spanCount == 0) {
                return true;
            }
        }
        return false;
    }
}