RecyclerView結構佈局：線性、網格、瀑布流，其中最常用的就是線性和網格佈局。

設定線性列表Item分割線一般比較容易，可以通過兩種方案來做：

1.  直接佈局item的時候，把要作為分割線的線條或者其他形式的，直接新增在item佈局中。並且可以動態控制分割線的顯示與否。
2. 通過RecyclerView.ItemDecoration來設定，無非就是設定左、右、上、下間隔

   public class RecyclerLinearSpaceItemDecoration extends RecyclerView.ItemDecoration {
   
       int mSpace;
       int type;
       //線性橫向：左間距
       private  final int HORIZONTAL_LEFT = 1;
       //線性橫向：右間距
       private  final int HORIZONTAL_RIGHT = 2;
   
       //線性縱向：top間距
       private  final int VERTICAL_TOP = 3;
       //線性縱向：bottom間距
       private  final int VERTICAL_BOTTOM = 4;
   
       /**
        * Retrieve any offsets for the given item. Each field of <code>outRect</code> specifies
        * the number of pixels that the item view should be inset by, similar to padding or margin.
        * The default implementation sets the bounds of outRect to 0 and returns.
        * <p>
        * <p>
        * If this ItemDecoration does not affect the positioning of item views, it should set
        * all four fields of <code>outRect</code> (left, top, right, bottom) to zero
        * before returning.
        * <p>
        * <p>
        * If you need to access Adapter for additional data, you can call
        * {@link RecyclerView#getChildAdapterPosition(View)} to get the adapter position of the
        * View.
        *
        * @param outRect Rect to receive the output.
        * @param view    The child view to decorate
        * @param parent  RecyclerView this ItemDecoration is decorating
        * @param state   The current state of RecyclerView.
        */
       @Override
       public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
           super.getItemOffsets(outRect, view, parent, state);
   //        int position = parent.getChildAdapterPosition(view);
           switch (type) {
               case HORIZONTAL_LEFT:
                   outRect.left = mSpace;
                   break;
               case HORIZONTAL_RIGHT:
                   outRect.right = mSpace;
                   break;
               case VERTICAL_TOP:
                   outRect.top = mSpace;
                   break;
               case VERTICAL_BOTTOM:
                   outRect.bottom = mSpace;
                   break;
           }
   
       }
   
       public RecyclerLinearSpaceItemDecoration(int space, int type) {
           this.mSpace = space;
           this.type = type;
       }
   
   }

設定網格佈局Item的分割線，目前只實踐過可以通過RecyclerView.ItemDecoration來設定，無非就是設定左、右、上、下間隔

public class RecyclerGridSpacingItemDecoration extends RecyclerView.ItemDecoration {

    private int spanCount;
    private int spacing;
    private boolean includeEdge;
    private Context context;
    private int styleType;

    //相同的間隔：橫向、縱向、以及頭部和底部
    private final int STYLE_TYPE_HEAD_FOOT_HORIZONTAL_VERTIAL = 1;
    //相同的間隔：只有橫向、縱向， 沒有頭部和底部
    private final int STYLE_TYPE_HORIZONTAL_VERTIAL = 2;

    public RecyclerGridSpacingItemDecoration(Context context, int spanCount, int spacing, int styleType ,boolean includeEdge) {
        this.spanCount = spanCount;
        this.spacing = spacing;
        this.includeEdge = includeEdge;
        this.context = context;
        this.styleType = styleType;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        int position = parent.getChildAdapterPosition(view); // item position
        int column = position % spanCount; // item column

        if (includeEdge) {
            outRect.left = spacing - column * spacing / spanCount; // spacing - column * ((1f / spanCount) * spacing)
            outRect.right = (column + 1) * spacing / spanCount; // (column + 1) * ((1f / spanCount) * spacing)

            if (position < spanCount) { // top edge
                outRect.top = spacing;
            }
//            outRect.bottom = spacing; // item bottom
        } else {

            outRect.left = column * spacing / spanCount; // column * ((1f / spanCount) * spacing)

            outRect.right = spacing - (column + 1) * spacing / spanCount; // spacing - (column + 1) * ((1f /    spanCount) * spacing)

            switch (styleType) {
                case STYLE_TYPE_HEAD_FOOT_HORIZONTAL_VERTIAL:
                    //底部有間隔的話，就用top
                    outRect.bottom = spacing;
                    if (position < spanCount) {
                        outRect.top = spacing;
                    }
                    break;
                case STYLE_TYPE_HORIZONTAL_VERTIAL:
                    if (position >= spanCount) {
                        //底部沒有間隔的話，就用top
                        outRect.top = spacing;
                    }
                    break;
            }
        }
    }

}