给RecyclerView添加分割线的步骤

【吐槽】RecyclerView没有提供分割线的方法，想要加个线还要自己画，点击事件的监听都要自己实现，不过真的好用。

给RecyclerView添加分割线的步骤

1, 新建类继承于RecyclerView.ItemDecoration，此为是抽象类:

    public static abstract class ItemDecoration {    public void onDraw(Canvas c, RecyclerView parent, State state) {        onDraw(c, parent);    }    public void onDrawOver(Canvas c, RecyclerView parent, State state) {        onDrawOver(c, parent);    }    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, State state) {        getItemOffsets(outRect, ((LayoutParams) view.getLayoutParams()).getViewLayoutPosition(),                parent);    }}
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“onDraw和onDrawOver,显然，这两个方法是用于绘制的，那么绘制分割线的逻辑可以放在这里面，它们二者的具体区别是：onDraw是在item view绘制之前调用，而onDrawOver是在item view绘制之后调用，因此我们一般选择重写其中一个方法即可。getItemOffsets，这个方法是告诉RecyclerView在绘制完一个item view的时候，应该留下多少空位，以便于绘制分割线。”

好像逻辑也不难，但是真的好麻烦，比如我要给我的瀑布流布局加一条系统自带的分割线，系统自带的就行，那我要新建一个实现类：

public class DividerItemDecoration extends RecyclerView.ItemDecoration {        //使用系统自带的listDivider        private static final int[] ATTRS = new int[]{                android.R.attr.listDivider        };        private Drawable mDivider;        public DividerItemDecoration(Context context) {            super();            // 从TypedArray中得到一个Drawable对象            final TypedArray typedArray = context.obtainStyledAttributes(ATTRS);            mDivider = typedArray.getDrawable(0);            typedArray.recycle();        }        @Override        public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {            super.onDraw(c, parent, state);            drawDivider(c, parent);        }        /**         * 遍历childView，为每一个childView描绘divider         * @param c 画布对象         * @param parent 父控件即RecyclerView         */        private void drawDivider(Canvas c, RecyclerView parent) {            //获取分割线的上边距，即RecyclerView的padding值            final int top = parent.getPaddingTop();            //分割线下边距            final int bottom = parent.getHeight() - parent.getPaddingBottom();            final int childCount = parent.getChildCount();            //遍历所有item view，为它们的右边方绘制分割线，就是计算出上下左右四个值画一个矩形            for (int i = 0; i < childCount; i++) {                final View child = parent.getChildAt(i);                final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();                final int left = child.getRight() + params.rightMargin;                final int right = left + mDivider.getIntrinsicWidth();                //画右边的divider                mDivider.setBounds(left, top, right, bottom);                mDivider.draw(c);                //画完右边画底边                mDivider.setBounds(child.getLeft() + child.getPaddingLeft(), child.getBottom() + params.bottomMargin,                        child.getRight() - child.getPaddingRight(), child.getBottom() + mDivider.getIntrinsicHeight());                mDivider.draw(c);            }        }        @Override        public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {            super.getItemOffsets(outRect, view, parent, state);            outRect.set(0, 0, mDivider.getIntrinsicHeight(), mDivider.getIntrinsicHeight());        }    }
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2, 为RecyclerView添加写好的ItemDecoration即可

mRecyclerView.addItemDecoration(new DividerItemDecoration(this));
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3, 没有3。

其实从 RecyclerView.ItemDecoration 的名字就看得出来，它是RecyclerView的item的装饰品，也就是说，除了画分割线，想画什么都是可以