關於RecylerView分割線的問題，當佈局形式為線性佈局LinearLayoutManager的時候， 官方提供了一個定義好的分割線類DividerItemDecoration，但是當佈局形式為網格佈局GridLayoutManager的時候，官方沒有提供分割線的相關類，需要自己去實現，網上大多網格佈局分割線的實現都是item中間有間隔，列表四周沒有分割的，所以我這裡定義一個item四周也有分割間隙的網格佈局分割線GridItemDivider。

程式碼比較簡單，主要思路是：我們要判斷itemview在recylerview中的四種位置；

1. item是第一個，那麼四周都有分割線

2. item是第一行，畫上、下、右三邊的分割線

3. item是第一列，畫左、右、下三邊的分割線

4.其他情況，畫右、下兩邊的分割線

以上四種情況依次用if和else if 去判斷，重寫RecyclerView.ItemDecoration的getItemOffsets，分別對以上四種情況進行對應的itemview的縮排。下面的完整程式碼：

public class GridItemDivider extends RecyclerView.ItemDecoration {

    private String TAG = getClass().getSimpleName();
    private static final int[] ATTRS = new int[]{android.R.attr.listDivider};
    private Drawable divider;

    public GridItemDivider(Context context) {
        final TypedArray a = context.obtainStyledAttributes(ATTRS);
        divider = a.getDrawable(0);
        a.recycle();
    }

    public GridItemDivider(Drawable drawable) {
        divider = drawable;
    }

    public GridItemDivider(int height, int color) {
        GradientDrawable shapeDrawable = new GradientDrawable();
        shapeDrawable.setColor(color);
        shapeDrawable.setShape(GradientDrawable.RECTANGLE);
        shapeDrawable.setSize(height, height);
        divider = shapeDrawable;
    }


    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {

        drawHorizontal(c, parent);
        drawVertical(c, parent);

    }

    private int getSpanCount(RecyclerView parent) {
        // 列數
        int spanCount = -1;
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager) {

            spanCount = ((GridLayoutManager) layoutManager).getSpanCount();
        } else if (layoutManager instanceof StaggeredGridLayoutManager) {
            spanCount = ((StaggeredGridLayoutManager) layoutManager)
                    .getSpanCount();
        }
        return spanCount;
    }

    public void drawHorizontal(Canvas c, RecyclerView parent) {
        int childCount = parent.getChildCount(); //獲取可見item的數量
        int spanCount = getSpanCount(parent);
        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
                    + divider.getIntrinsicWidth();
            final int top = child.getBottom() + params.bottomMargin;
            final int bottom = top + divider.getIntrinsicHeight();
            divider.setBounds(left, top, right, bottom);
            divider.draw(c);
            if (i < spanCount) { //畫第一行頂部的分割線
                drawHorizontalForFirstRow(c, child);
            }
        }
    }

    private void drawHorizontalForFirstRow(Canvas c, View child) {
        final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                .getLayoutParams();
        int left = child.getLeft() - params.leftMargin - divider.getIntrinsicWidth();
        int top = child.getTop() - params.topMargin - divider.getIntrinsicHeight();
        int right = child.getRight() + params.rightMargin + divider.getIntrinsicWidth();
        int bottom = top + divider.getIntrinsicHeight();
        divider.setBounds(left, top, right, bottom);
        divider.draw(c);
    }

    private void drawVerticalForFirstColum(Canvas c, View child) {
        final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                .getLayoutParams();
        int left = child.getLeft() - params.leftMargin - divider.getIntrinsicWidth();
        int top = child.getTop() - params.topMargin;
        int right = child.getLeft() - params.leftMargin;
        int bottom = top + child.getHeight() + divider.getIntrinsicHeight();
        divider.setBounds(left, top, right, bottom);
        divider.draw(c);
    }

    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 + divider.getIntrinsicWidth();
            divider.setBounds(left, top, right, bottom);
            divider.draw(c);
            if (isFirstColum(parent, i, getSpanCount(parent))) { //畫第一列左邊分割線
                drawVerticalForFirstColum(c, child);
            }
        }
    }

    private boolean isLastColum(RecyclerView parent, int pos, int spanCount,
                                int childCount) {
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager) {
            if ((pos + 1) % spanCount == 0)// 如果是最後一列，則不需要繪製右邊
            {
                return true;
            }
        } else if (layoutManager instanceof StaggeredGridLayoutManager) {
            int orientation = ((StaggeredGridLayoutManager) layoutManager)
                    .getOrientation();
            if (orientation == StaggeredGridLayoutManager.VERTICAL) {
                if ((pos + 1) % spanCount == 0)// 如果是最後一列，則不需要繪製右邊
                {
                    return true;
                }
            } else {
                childCount = childCount - childCount % spanCount;
                if (pos >= childCount)// 如果是最後一列，則不需要繪製右邊
                    return true;
            }
        }
        return false;
    }

    private boolean isLastRaw(RecyclerView parent, int pos, int spanCount,
                              int childCount) {
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager) {
            childCount = childCount - childCount % spanCount;
            if (pos >= childCount)// 如果是最後一行，則不需要繪製底部
                return true;
        } else if (layoutManager instanceof StaggeredGridLayoutManager) {
            int orientation = ((StaggeredGridLayoutManager) layoutManager)
                    .getOrientation();
            if (orientation == StaggeredGridLayoutManager.VERTICAL) {
                childCount = childCount - childCount % spanCount;
                // 如果是最後一行，則不需要繪製底部
                if (pos >= childCount)
                    return true;
            } else
            {
                // 如果是最後一行，則不需要繪製底部
                if ((pos + 1) % spanCount == 0) {
                    return true;
                }
            }
        }
        return false;
    }

    //是否為第一列
    private boolean isFirstColum(RecyclerView parent, int pos, int spanCount) {
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager) { //網格佈局
            if ((pos + 1) % spanCount == 1) {
                return true;
            }
        }
        return false;
    }

    //是否為第一行
    private boolean isFirstRaw(int pos, int spanCount) {
        if (pos < spanCount) {
            return true;
        }
        return false;
    }

    @Override
    public void getItemOffsets(Rect outRect, int itemPosition,
                               RecyclerView parent) {
        int spanCount = getSpanCount(parent); //列數

        if (itemPosition == 0) { //第一行第一個，四邊都畫
            outRect.set(divider.getIntrinsicWidth(), divider.getIntrinsicHeight(),
                    divider.getIntrinsicWidth(), divider.getIntrinsicHeight());
        } else if (isFirstRaw(itemPosition, spanCount)) { //第一行，畫上下右三邊
            outRect.set(0, divider.getIntrinsicHeight(), divider.getIntrinsicWidth(), divider.getIntrinsicHeight());
        } else if (isFirstColum(parent, itemPosition, spanCount)) { //第一列，畫左右下三邊
            outRect.set(divider.getIntrinsicWidth(), 0, divider.getIntrinsicWidth(), divider.getIntrinsicHeight());
        } else { //其他，畫右下兩邊
            outRect.set(0, 0, divider.getIntrinsicWidth(), divider.getIntrinsicHeight());
        }

    }

}
 

程式碼比較簡單明瞭， 我就不詳細多說了，感謝大家支援！！