安卓RecyclerView萬能分割線

參考後修改的，參考源暫時找不到了，非常感謝大神當年的幫助。
RecyclerView 的分割線可以通過item 佈局去畫，但是這樣效率太低了，想在百度上找一篇用着舒爽的文章又太難了。
下面請看懶人分享第二章：萬能分割線。

 //使用方法：
//參數分別是 上下文、寬度、顏色
 rvMy.addItemDecoration(
         new DividerItemDecoration(
             getMyActivity(), 3, 0xffdddddd)
             );

*****************************************************************
//自定義分割
public class DividerItemDecoration extends BaseDividerItemDecoration {

public DividerItemDecoration(Context context,
    int  lineWidthDp, @ColorInt int colorRGB) {
        super(context, lineWidthDp, colorRGB);
    }

    @Override
    public boolean[] getItemSidesIsHaveOffsets(int itemPosition) {
        //順時針順序:left, top, right, bottom
        boolean[] isOffset = {false, false, true, true};
        //默認只有bottom顯示分割線
        return isOffset;
    }
}


//工具代碼
*******************************************************************

package com.xdx.hostay.customer;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Rect;
import android.support.annotation.ColorInt;
import android.support.v7.widget.RecyclerView;
import android.view.View;

/**
 * Created by biyunlong on 2017/5/17.
 * Make progress every day
 */
public abstract class BaseDividerItemDecoration extends RecyclerView.ItemDecoration {

    private Paint mPaint;
    private int lineWidth;//px 分割線寬
    /**
     * A single color value in the form 0xAARRGGBB.
     **/
    private int colorRGB;

    public BaseDividerItemDecoration(Context context, float lineWidthDp, @ColorInt int colorRGB) {
        this.colorRGB = colorRGB;
//        this.lineWidth = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, lineWidthDp, context.getResources().getDisplayMetrics());

        this.lineWidth= (int) lineWidthDp;
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mPaint.setColor(colorRGB);
        mPaint.setStyle(Paint.Style.FILL);
    }

    public BaseDividerItemDecoration(Context context, int lineWidthDp, @ColorInt int colorRGB) {
        this.colorRGB = colorRGB;
        this.lineWidth= lineWidthDp;
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mPaint.setColor(colorRGB);
        mPaint.setStyle(Paint.Style.FILL);
    }


    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        int childCount1 = parent.getChildCount();
        for (int i = 0; i < childCount1; i++) {
            View child = parent.getChildAt(i);

            int itemPosition = ((RecyclerView.LayoutParams) child.getLayoutParams()).getViewLayoutPosition();

            boolean[] sideOffsetBooleans = getItemSidesIsHaveOffsets(itemPosition);
            if (sideOffsetBooleans[0]) {
                drawChildLeftVertical(child, c, parent);
            }
            if (sideOffsetBooleans[1]) {
                drawChildTopHorizontal(child, c, parent);
            }
            if (sideOffsetBooleans[2]) {
                drawChildRightVertical(child, c, parent);
            }
            if (sideOffsetBooleans[3]) {
                drawChildBottomHorizontal(child, c, parent);
            }
        }
    }

    private void drawChildBottomHorizontal(View child, Canvas c, RecyclerView parent) {

        RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                .getLayoutParams();
        int left = child.getLeft() - params.leftMargin - lineWidth;
        int right = child.getRight() + params.rightMargin + lineWidth;
        int top = child.getBottom() + params.bottomMargin;
        int bottom = top + lineWidth;

        c.drawRect(left, top, right, bottom, mPaint);

    }

    private void drawChildTopHorizontal(View child, Canvas c, RecyclerView parent) {
        RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                .getLayoutParams();
        int left = child.getLeft() - params.leftMargin - lineWidth;
        int right = child.getRight() + params.rightMargin + lineWidth;
        int bottom = child.getTop() - params.topMargin;
        int top = bottom - lineWidth;

        c.drawRect(left, top, right, bottom, mPaint);

    }

    private void drawChildLeftVertical(View child, Canvas c, RecyclerView parent) {
        RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                .getLayoutParams();
        int top = child.getTop() - params.topMargin - lineWidth;
        int bottom = child.getBottom() + params.bottomMargin + lineWidth;
        int right = child.getLeft() - params.leftMargin;
        int left = right - lineWidth;

        c.drawRect(left, top, right, bottom, mPaint);

    }

    private void drawChildRightVertical(View child, Canvas c, RecyclerView parent) {
        RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                .getLayoutParams();
        int top = child.getTop() - params.topMargin - lineWidth;
        int bottom = child.getBottom() + params.bottomMargin + lineWidth;
        int left = child.getRight() + params.rightMargin;
        int right = left + lineWidth;

        c.drawRect(left, top, right, bottom, mPaint);

    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {

        //outRect 看源碼可知這裏只是把Rect類型的outRect作爲一個封裝了left,right,top,bottom的數據結構,
        //作爲傳遞left,right,top,bottom的偏移值來用的

        int itemPosition = ((RecyclerView.LayoutParams) view.getLayoutParams()).getViewLayoutPosition();
        //
        boolean[] sideOffsetBooleans = getItemSidesIsHaveOffsets(itemPosition);

        int left = sideOffsetBooleans[0] ? lineWidth : 0;
        int top = sideOffsetBooleans[1] ? lineWidth : 0;
        int right = sideOffsetBooleans[2] ? lineWidth : 0;
        int bottom = sideOffsetBooleans[3] ? lineWidth : 0;

        outRect.set(left, top, right, bottom);
    }

    /**
     * 順序:left, top, right, bottom
     *
     * @return boolean[4]
     */
    public abstract boolean[] getItemSidesIsHaveOffsets(int itemPosition);


}