设置下划线

1. recycleView本身并没有添加下划线的方法,但是可以addDecoration.通过Decoration重写onDraw方法来自己画出想要的效果.

 mRecyclerView.addItemDecoration(new RecyclerViewDecoration(mContext,RecyclerViewDecoration.VERTICAL_LIST));

2. RecyclerView.ItemDecoration

public class RecyclerViewDecoration extends RecyclerView.ItemDecoration {

    private Context mContext;
    private Drawable mDivider;
    private int mOrientation;
    public static final int HORIZONTAL_LIST = LinearLayoutManager.HORIZONTAL;
    public static final int VERTICAL_LIST = LinearLayoutManager.VERTICAL;

    public static final int[] ATRRS  = new int[]{
            android.R.attr.listDivider
    };

    public RecyclerViewDecoration(Context context, int orientation) {
        mContext = context;
        mOrientation = orientation;
        TypedArray typedArray = context.obtainStyledAttributes(ATRRS);
        mDivider = typedArray.getDrawable(0);
        typedArray.recycle();
        setOrientation(orientation);
    }

    public void setOrientation(int orientation){
        if (orientation != HORIZONTAL_LIST && orientation != VERTICAL_LIST){
            throw new IllegalArgumentException("invalid orientation");        }
            mOrientation = orientation;
    }


    @Override//这里可以实现类似于padding值的边距效果
    public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        if(mOrientation == HORIZONTAL_LIST){
            //画横线，就是往下偏移一个分割线的高度
            outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
        }else {
            //画竖线，就是往右偏移一个分割线的宽度
            outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
        }
    }

    @Override//画线
    public void onDraw(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        if (mOrientation == HORIZONTAL_LIST){
            drawVerticalLine(c, parent, state);
        }else {
            drawHorizontalLine(c, parent, state);
        }
    }

    @Override
    public void onDrawOver(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.onDrawOver(c, parent, state);
    }

    //画横线, 这里的parent其实是显示在屏幕显示的这部分
    public void drawHorizontalLine(Canvas c, RecyclerView parent, RecyclerView.State state){
        int left = parent.getPaddingLeft();
        int right = parent.getWidth() - parent.getPaddingRight();
        final int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++){
            final View child = parent.getChildAt(i);

            //获得child的布局信息
            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams)child.getLayoutParams();
            final int top = child.getBottom() + params.bottomMargin;
            final int bottom = top + mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
            //Log.d("wnw", left + " " + top + " "+right+"   "+bottom+" "+i);
        }
    }

    //画竖线
    public void drawVerticalLine(Canvas c, RecyclerView parent, RecyclerView.State state){
        int top = parent.getPaddingTop();
        int bottom = parent.getHeight() - parent.getPaddingBottom();
        final int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++){
            final View child = parent.getChildAt(i);

            //获得child的布局信息
            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams)child.getLayoutParams();
            final int left = child.getRight() + params.rightMargin;
            final int right = left + mDivider.getIntrinsicWidth();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }
}

上边是获取的Android系统中的横线,当然你也可以通过Paint来画.