RecyclerView自定义Grid网格布局分割线

引用的 https://www.jianshu.com/p/a436f5cec559

public class ItemGridDecoration extends RecyclerView.ItemDecoration {

private static final int[] ATTRS = new int[]{android.R.attr.listDivider};

private Drawable mDivider;

private int spanCount = -1;

//height width 单位为px

private int width = 5;

private Paint paint;

public ItemGridDecoration(Context context) {
    init(context, width, android.R.color.black);
}

public ItemGridDecoration(Context context, int width) {
    init(context, width, android.R.color.black);
}

public ItemGridDecoration(Context context, int width, int color) {
    init(context, width, color);
}

private void init(Context context, int width, int color) {
    this.width = width;
    paint = new Paint();
    paint.setColor(context.getResources().getColor(color));
    final TypedArray a = context.obtainStyledAttributes(ATTRS);
    mDivider = a.getDrawable(0);
    a.recycle();
}

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

@Override
public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
    int position = parent.getChildAdapterPosition(view);
    int childCount = parent.getAdapter().getItemCount();
    int spanCount = getSpanCount(parent);
    int drawRight = width;
    int drawBottom = width;
    int drawLeft = width;
    int drawTop = width;
    if (isLastRaw(parent, position, spanCount, childCount)) {
        drawBottom = 0;
    }
    if (isFirstRaw(parent, position, spanCount, childCount)) {
        drawTop = 0;
    }
    if (isLastColum(parent, position, spanCount, childCount)) {
        drawRight = 0;
    }
    if (isFirstColum(parent, position, spanCount, childCount)) {
        drawLeft = 0;
    }
    if (isLastItem(parent, position, childCount)) {
        drawRight = 0;
    }
    outRect.set(drawLeft, drawTop, drawRight, drawBottom);
}

private void drawHorizontal(Canvas c, RecyclerView parent) {
    spanCount = getSpanCount(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;
        int right = child.getRight() + params.rightMargin;
        final int top = child.getBottom() + params.bottomMargin;
        //            int bottom = top + mDivider.getIntrinsicHeight();
        int bottom = top + width * 2;
        if (isLastRaw(parent, i, spanCount, childCount)) {
            // 如果是最后一行，则不需要绘制底部
            bottom = top;
        }
        if (!isLastColum(parent, i, spanCount, childCount)) {
            right = child.getRight() + params.rightMargin + width * 2;

        }
        mDivider.setBounds(left, top, right, bottom);
        mDivider.draw(c);
        c.drawRect(left, top, right, bottom, paint);
    }
}

private void drawVertical(Canvas c, RecyclerView parent) {
    spanCount = getSpanCount(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;
        //            int right = left + mDivider.getIntrinsicWidth();
        int right = left + width * 2;

        if (isLastColum(parent, i, spanCount, childCount)) {
            // 如果是最后一列，则不需要绘制右边
            right = left;
        }
        if (isLastItem(parent, i, childCount)) {
            right = left;
        }
        mDivider.setBounds(left, top, right, bottom);
        mDivider.draw(c);
        c.drawRect(left, top, right, bottom, paint);
    }
}

private int getSpanCount(RecyclerView parent) {
    // 列数
    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;
}

private boolean isLastRaw(RecyclerView parent, int pos, int spanCount, int childCount) {
    RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
    if (layoutManager instanceof GridLayoutManager) {
        if (childCount % spanCount == 0) {
            childCount = childCount - spanCount;
        } else {
            childCount = childCount - childCount % spanCount;
        }
        if (pos >= childCount) {
            // 如果是最后一行，则不需要绘制底部
            return true;
        }
    } else if (layoutManager instanceof StaggeredGridLayoutManager) {
        int orientation = ((StaggeredGridLayoutManager) layoutManager)
                .getOrientation();
        // StaggeredGridLayoutManager 且纵向滚动
        if (orientation == StaggeredGridLayoutManager.VERTICAL) {
            childCount = childCount - childCount % spanCount;
            // 如果是最后一行，则不需要绘制底部
            if (pos >= childCount)
                return true;
        } else {
            // 如果是最后一行，则不需要绘制底部
            if ((pos + 1) % spanCount == 0) {
                return true;
            }
        }
    }
    return false;
}

private boolean isFirstRaw(RecyclerView parent, int pos, int spanCount, int childCount) {
    RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
    if (layoutManager instanceof GridLayoutManager) {
        if (pos < spanCount) {
            // 如果是第一行，则不需要绘制底部
            return true;
        }
    } else if (layoutManager instanceof StaggeredGridLayoutManager) {
        int orientation = ((StaggeredGridLayoutManager) layoutManager)
                .getOrientation();
        // StaggeredGridLayoutManager 且纵向滚动
        if (orientation == StaggeredGridLayoutManager.VERTICAL) {
            if (pos < spanCount) {
                // 如果是第一行，则不需要绘制底部
                return true;
            }
        } else {
            // 如果是第一行，则不需要绘制底部
            if ((pos + 1) % spanCount == 1) {
                return true;
            }
        }
    }
    return false;
}

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) {// 如果是最后一列，则不需要绘制右边
            return true;
        }
        if ((pos + 1) % spanCount == 1 && childCount == 1) {// 如果是最后一列，则不需要绘制右边
            return true;
        }
    } else if (layoutManager instanceof StaggeredGridLayoutManager) {
        int orientation = ((StaggeredGridLayoutManager) layoutManager)
                .getOrientation();
        if (orientation == StaggeredGridLayoutManager.VERTICAL) {
            if ((pos + 1) % spanCount == 0) {// 如果是最后一列，则不需要绘制右边
                return true;
            }
        } else {
            childCount = childCount - childCount % spanCount;
            if (pos >= childCount)// 如果是最后一列，则不需要绘制右边
                return true;
        }
    }
    return false;
}

private boolean isFirstColum(RecyclerView parent, int pos, int spanCount, int childCount) {
    RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
    if (layoutManager instanceof GridLayoutManager) {
        if ((pos + 1) % spanCount == 1) {
            return true;
        }
    } else if (layoutManager instanceof StaggeredGridLayoutManager) {
        int orientation = ((StaggeredGridLayoutManager) layoutManager).getOrientation();
        if (orientation == StaggeredGridLayoutManager.VERTICAL) {
            if ((pos + 1) % spanCount == 1) {
                return true;
            }
        } else {
            if (pos < spanCount) {
                return true;
            }
        }
    }
    return false;
}

private boolean isLastItem(RecyclerView parent, int pos, int childCount) {
    RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
    if (layoutManager instanceof GridLayoutManager) {
        if ((pos + 1) == childCount) {
            return true;
        }
    }
    return false;
}

用法
recycleView.addItemDecoration(new ItemGridDecoration(this, dip2px(4), R.color.red));