RecyclerView（二） ItemDecoration-优快云博客

本文深入讲解了RecyclerView中ItemDecoration的作用及使用方法，包括内置的DividerItemDecoration和自定义ItemDecoration的实现过程，以及如何通过onDraw和onDrawOver方法进行绘制。

一.什么是ItemDecoration

ItemDecoration提供了对RecyclerView中Item对装饰

二. 简单应用

 DividerItemDecoration dividerItemDecoration = new DividerItemDecoration(this, DividerItemDecoration.VERTICAL);
        mRecyclerView.addItemDecoration(dividerItemDecoration);

三.自定义ItemDecoration

class MyItemDecoration extends  RecyclerView.ItemDecoration{
        @Override
        public void onDraw(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
            super.onDraw(c, parent, state);
            RecyclerView.LayoutManager manager = parent.getLayoutManager();
            for (int i = 0; i < parent.getChildCount(); i++) {
                View view = parent.getChildAt(i);
                int decoratedLeft = manager.getLeftDecorationWidth(view);
                int cx = decoratedLeft/2;
                int cy = view.getTop() + view.getHeight()/2;
                c.drawCircle(cx,cy,20,new Paint());

            }
        }

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

        @Override
        public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
            super.getItemOffsets(outRect, view, parent, state);
            outRect.left = 100;
            outRect.bottom = 1;
        }

    }

Rect outRect指的是item的上下左右间距，可在onDraw中对间距空间绘制，ItemDecoration与Item的绘制顺序为：decoration 的 onDraw->item的 onDraw->decoration 的 onDrawOver，这三者是依次发生的。