griddivider set divider in grid form modified from simple-item-decoration

GridDividerItemDecoration

package com.meixun.b2b.mall.supplier.adapter.decoration;

import android.graphics.Canvas;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.support.v7.widget.RecyclerView;
import android.view.View;

/**
 * Adds interior dividers to a RecyclerView with a GridLayoutManager.
 */
public class GridDividerItemDecoration extends RecyclerView.ItemDecoration {

    private Drawable mHorizontalDivider;
    private Drawable mVerticalDivider;
    private int mNumColumns;

    /**
     * Sole constructor. Takes in {@link Drawable} objects to be used as
     * horizontal and vertical dividers.
     *
     * @param horizontalDivider A divider {@code Drawable} to be drawn on the
     *                          rows of the grid of the RecyclerView
     * @param verticalDivider A divider {@code Drawable} to be drawn on the
     *                        columns of the grid of the RecyclerView
     * @param numColumns The number of columns in the grid of the RecyclerView
     */
    public GridDividerItemDecoration(Drawable horizontalDivider, Drawable verticalDivider, int numColumns) {
        mHorizontalDivider = horizontalDivider;
        mVerticalDivider = verticalDivider;
        mNumColumns = numColumns;
    }

    /**
     * Draws horizontal and/or vertical dividers onto the parent RecyclerView.
     *
     * @param canvas The {@link Canvas} onto which dividers will be drawn
     * @param parent The RecyclerView onto which dividers are being added
     * @param state The current RecyclerView.State of the RecyclerView
     */
    @Override
    public void onDraw(Canvas canvas, RecyclerView parent, RecyclerView.State state) {


    }

    @Override
    public void onDrawOver(Canvas canvas, RecyclerView parent, RecyclerView.State state) {
        drawHorizontalDividers(canvas, parent);
        drawVerticalDividers(canvas, parent);
    }

    /**
     * Determines the size and location of offsets between items in the parent
     * RecyclerView.
     *
     * @param outRect The {@link Rect} of offsets to be added around the child view
     * @param view The child view to be decorated with an offset
     * @param parent The RecyclerView onto which dividers are being added
     * @param state The current RecyclerView.State of the RecyclerView
     */
    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);

        boolean childIsInLeftmostColumn = (parent.getChildAdapterPosition(view) % mNumColumns) == 0;
        if (!childIsInLeftmostColumn) {
            outRect.left = mHorizontalDivider.getIntrinsicWidth();
        }

        boolean childIsInFirstRow = (parent.getChildAdapterPosition(view)) < mNumColumns;
        if (!childIsInFirstRow) {
            outRect.top = mVerticalDivider.getIntrinsicHeight();
        }
    }

    /**
     * Adds horizontal dividers to a RecyclerView with a GridLayoutManager or its
     * subclass.
     *
     * @param canvas The {@link Canvas} onto which dividers will be drawn
     * @param parent The RecyclerView onto which dividers are being added
     */
    private void drawHorizontalDividers(Canvas canvas, RecyclerView parent) {
        int childCount = parent.getChildCount();
        int rowCount = childCount / mNumColumns;
        int lastRowChildCount = childCount % mNumColumns;

        for (int i = 1; i < mNumColumns && i < childCount; i++) {
            int lastRowChildIndex;
            if (i < lastRowChildCount) {
                lastRowChildIndex = i + (rowCount * mNumColumns);
            } else {
                lastRowChildIndex = i + ((rowCount - 1) * mNumColumns);
            }

            View firstRowChild = parent.getChildAt(i);
            View lastRowChild = parent.getChildAt(lastRowChildIndex);

            int dividerTop = firstRowChild.getTop();
            int dividerRight = firstRowChild.getLeft();
            int dividerLeft = dividerRight - mHorizontalDivider.getIntrinsicWidth();
            int dividerBottom = lastRowChild.getBottom();

            mHorizontalDivider.setBounds(dividerLeft, dividerTop, dividerRight, dividerBottom);
            mHorizontalDivider.draw(canvas);
        }
    }

    /**
     * Adds vertical dividers to a RecyclerView with a GridLayoutManager or its
     * subclass.
     *
     * @param canvas The {@link Canvas} onto which dividers will be drawn
     * @param parent The RecyclerView onto which dividers are being added
     */
    private void drawVerticalDividers(Canvas canvas, RecyclerView parent) {
        int childCount = parent.getChildCount();
        int rowCount = childCount / mNumColumns;
        int rightmostChildIndex;
        // in case of one row, we do not need draw vertical divider
        if (childCount == mNumColumns) {
            return;
        }

        for (int i = 1; i <= rowCount ; i++) {
            if (i == rowCount ) {
                rightmostChildIndex = childCount - 1;
            } else {
                rightmostChildIndex = (i * mNumColumns) + mNumColumns - 1;
            }

            View leftmostChild = parent.getChildAt(i * mNumColumns);
            View rightmostChild = parent.getChildAt(rightmostChildIndex);

            int dividerLeft = leftmostChild.getLeft();
            int dividerBottom = leftmostChild.getTop();
            int dividerTop = dividerBottom - mVerticalDivider.getIntrinsicHeight();
            int dividerRight = rightmostChild.getRight();

            mVerticalDivider.setBounds(dividerLeft, dividerTop, dividerRight, dividerBottom);
            mVerticalDivider.draw(canvas);
        }
    }
}