Android RecyclerView 设置分割线(item头部也绘制)

查了下资料，RecyclerView的分割线网上资料很多

但是头部也绘制的分割线资料挺少

于是参考一下资料自己弄一个头部也绘制的分割线

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LinearLayout的分割线DividerItemDecoration

public class DividerItemDecoration extends RecyclerView.ItemDecoration {
    private static final int[] ATTRS = new int[]{android.R.attr.listDivider};

    private Drawable mDivider;

    /**
     * Default divider will be used
     */
    public DividerItemDecoration(Context context) {
        final TypedArray styledAttributes = context.obtainStyledAttributes(ATTRS);
        mDivider = styledAttributes.getDrawable(0);
        styledAttributes.recycle();
    }

    /**
     * Custom divider will be used
     */
    public DividerItemDecoration(Context context, int resId) {
        mDivider = ContextCompat.getDrawable(context, resId);
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        int column_num = getSpanCount(parent);
        int left = parent.getPaddingLeft();
        int right = parent.getWidth() - parent.getPaddingRight();
        int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            View child = parent.getChildAt(i);

            RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();

            int top = 0;
            int bottom = 0;
            //根据item的数量判断是否为第一个
            if (i / column_num == 0) {
                //画item最上面的分割线
                top = 0;
                bottom = top + mDivider.getIntrinsicHeight();
                mDivider.setBounds(left, top, right, bottom);
                mDivider.draw(c);
                //画item下面的分割线
                top = child.getBottom() + params.bottomMargin;
                bottom = top + mDivider.getIntrinsicHeight();
                mDivider.setBounds(left, top, right, bottom);
                mDivider.draw(c);
            } else {
                //画item下面的分割线
                top = child.getBottom() + params.bottomMargin;
                bottom = top + mDivider.getIntrinsicHeight();
                mDivider.setBounds(left, top, right, bottom);
                mDivider.draw(c);
            }

        }
    }

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

GridLayout的分割线DividerGridItemDecoration

这个是参考这个的RecyclerView中利用GridLayoutManager实现item四周都带有分割线效果

public class DividerGridItemDecoration extends RecyclerView.ItemDecoration {

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

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

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

    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;
    }

    public void drawHorizontal(Canvas c, RecyclerView parent) {
        int childCount = parent.getChildCount();
        int column_num = 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
                    + mDivider.getIntrinsicWidth();
//            final int top = child.getBottom() + params.bottomMargin;
//            final int bottom = top + mDivider.getIntrinsicHeight();
//            mDivider.setBounds(left, top, right, bottom);
//            mDivider.draw(c);
            int top = 0;
            int bottom = 0;

            if ((i / column_num) == 0) {
                //画item最上面的分割线
                top = 0;
                bottom = top + mDivider.getIntrinsicHeight();
                mDivider.setBounds(left, top, right, bottom);
                mDivider.draw(c);
                //画item下面的分割线
                top = child.getBottom() + params.bottomMargin;
                bottom = top + mDivider.getIntrinsicHeight();
                mDivider.setBounds(left, top, right, bottom);
                mDivider.draw(c);
            } else {
                //画item下面的分割线
                top = child.getBottom() + params.bottomMargin;
                bottom = top + mDivider.getIntrinsicHeight();
                mDivider.setBounds(left, top, right, bottom);
                mDivider.draw(c);

        }
    }

}

    public void drawVertical(Canvas c, RecyclerView parent) {
        final int childCount = parent.getChildCount();
        int column_num = 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 top = child.getTop() - params.topMargin;
            final int bottom = child.getBottom() + params.bottomMargin;
//            final int left = child.getRight() + params.rightMargin;
//            final int right = left + mDivider.getIntrinsicWidth();
//            mDivider.setBounds(left, top, right, bottom);
//            mDivider.draw(c);
            int left = 0;
            int right = 0;

            if ((i % column_num) == 0) {
                //item左边分割线
                left = 0;
                right = left + mDivider.getIntrinsicWidth();
                mDivider.setBounds(left, top, right, bottom);
                mDivider.draw(c);
                //item右边分割线
                left = child.getRight() + params.rightMargin;
                right = left + mDivider.getIntrinsicWidth();
            } else {
                left = child.getRight() + params.rightMargin;
                right = left + mDivider.getIntrinsicWidth();
            }

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

        }
    }

    private boolean isLastColum(RecyclerView parent, int pos, int spanCount, int childCount) {
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager) {
//            // 如果是最后一列，则不需要绘制右边
//            if ((pos + 1) % spanCount == 0) {
//                return true;
//            }
        } else if (layoutManager instanceof StaggeredGridLayoutManager) {
            int orientation = ((StaggeredGridLayoutManager) layoutManager)
                    .getOrientation();
            if (orientation == StaggeredGridLayoutManager.VERTICAL) {
                // 如果是最后一列，则不需要绘制右边
                if ((pos + 1) % spanCount == 0) {
                    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 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;
                if (pos >= childCount)// 如果是最后一行，则不需要绘制底部
                    return true;
                // StaggeredGridLayoutManager 且横向滚动
            } 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;
    }

    @Override
    public void getItemOffsets(Rect outRect, int itemPosition,
                               RecyclerView parent) {
        int spanCount = getSpanCount(parent);
        int childCount = parent.getAdapter().getItemCount();
        // 如果是最后一行，则不需要绘制底部
        if (isLastRaw(parent, itemPosition, spanCount, childCount)) {
            outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
            // 如果是最后一列，则不需要绘制右边
        } else if (isLastColum(parent, itemPosition, spanCount, childCount)) {
            outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
        } else {
            outRect.set(0, 0, mDivider.getIntrinsicWidth(),
                    mDivider.getIntrinsicHeight());
        }
    }
}