效果如下

image.png

分解：
1闻书、自定RecyclerView.ItemDecoration
2般哼、通過getItemOffsets 給每一個 Item 設置偏移量，相當于留出間距
3惠窄、通過onDraw 在留出的間距上繪制想要的邊線

源碼：

//主要是繪制了每一個item 的右邊和下邊線條蒸眠，最后一列的右邊沒有繪制，最后一行的底部不做繪制
public class GridSpaceItemDecoration extends RecyclerView.ItemDecoration {
    private int space;
    private Paint paint = new Paint();

    public GridSpaceItemDecoration() {
        space = SizeUtils.dp2px(1f);
        paint.setColor(Color.parseColor("#f7f7f7"));
        paint.setStrokeWidth(space);
    }

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

    //圖中橫向的紅色線條繪制杆融，為了便于區(qū)分設置的兩個顏色楞卡，代碼里已經(jīng)去掉
    public void drawHorizontal(Canvas c, RecyclerView parent) {
        int childCount = parent.getChildCount();
        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.getLeft() - params.leftMargin;
            final int right = child.getRight() + params.rightMargin + space;
            int top = child.getBottom() + params.bottomMargin;
            int bottom = top + space;
            c.drawRect(new Rect(left, top, right, bottom), paint);
        }
    }

   //圖中縱向的綠色線條繪制，為了便于區(qū)分設置的兩個顏色脾歇，代碼里已經(jīng)去掉
    public void drawVertical(Canvas c, RecyclerView parent) {
        final int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            final View child = parent.getChildAt(i);
            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
            final int top = child.getTop() - params.topMargin;
            final int bottom = child.getBottom() + params.bottomMargin;
            final int left = child.getRight() + params.rightMargin;
            final int right = left + space;
            c.drawRect(new Rect(left, top, right, bottom), paint);
        }
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent,
                               RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        int itemPosition = parent.getChildLayoutPosition(view);
        int spanCount = getSpanCount(parent);
        double count = Math.ceil((double) parent.getAdapter().getItemCount() / (double) spanCount);//總行數(shù)
        //double currentCount = Math.ceil((double) (itemPosition + 1) / spanCount);//當前行數(shù)
        if (count == 1) {
            // 如果是最后一列蒋腮，則不需要繪制右邊
            if (isLastColumn(itemPosition, parent)) {
                outRect.set(0, 0, 0, 0);
            } else {
                outRect.set(0, 0, space, 0);
            }
        } else {
            if (isLastRow(itemPosition, parent)) {
                if (isLastColumn(itemPosition, parent)) {
                    outRect.set(0, 0, 0, 0);
                } else {
                    outRect.set(0, 0, space, 0);
                }
            } else {
                if (isLastColumn(itemPosition, parent)) {
                    outRect.set(0, 0, 0, space);
                } else {
                    outRect.set(0, 0, space, space);
                }
            }
        }
    }


    private boolean isLastRow(int itemPosition, RecyclerView parent) {
        int spanCount = getSpanCount(parent);
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        //有多少列
        if (layoutManager instanceof GridLayoutManager) {
            int childCount = parent.getAdapter().getItemCount();

            double count = Math.ceil((double) childCount / (double) spanCount);//總行數(shù)
            double currentCount = Math.ceil((double) (itemPosition + 1) / spanCount);//當前行數(shù)

            //最后當前數(shù)量小于總的
            if (currentCount < count) {
                return false;
            }
        }
        return true;
    }

    private boolean isLastColumn(int itemPosition, RecyclerView parent) {
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        //有多少列
        if (layoutManager instanceof GridLayoutManager) {
            int spanCount = getSpanCount(parent);
            if ((itemPosition + 1) % spanCount == 0) {//因為是從0可以所以要將ItemPosition先加1
                return true;
            }
        }
        return false;
    }

    private int getSpanCount(RecyclerView parent) {
        if (parent.getLayoutManager() instanceof GridLayoutManager) {
            return ((GridLayoutManager) parent.getLayoutManager()).getSpanCount();
        } else {
            return 1;
        }
    }
}

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