public class StickyItemDecoration extends RecyclerView.ItemDecoration {

    private ISticky mISticky;
//矩形高度
private int mRectHeight;
//文字TextSize
private int mTextPaintSize;
    private Paint mTxtPaint;
    private Paint mRectPaint;
//分割線畫筆
private Paint mDividerPaint;
//手機狀態列的高度
private int mStatusBarHeight
 
;
    public StickyItemDecoration(Context context, int statusBarHeight, ISticky iSticky) {
        mStatusBarHeight=statusBarHeight;
mISticky=iSticky;
mRectHeight= (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,30,
context.getResources().getDisplayMetrics());
mTextPaintSize=(int) TypedValue.applyDimension
 
(TypedValue.COMPLEX_UNIT_DIP,17,
context.getResources().getDisplayMetrics());
mTxtPaint=new Paint(Paint.ANTI_ALIAS_FLAG);
mTxtPaint.setColor(Color.BLACK);
mTxtPaint.setTextSize(mTextPaintSize);
mRectPaint=new Paint(Paint.ANTI_ALIAS_FLAG);
mRectPaint.setStyle(Paint.Style.FILL);
mRectPaint.setColor(Color.parseColor
 
("#DDDDDD"));
mDividerPaint=new Paint(Paint.ANTI_ALIAS_FLAG);
mDividerPaint.setStyle(Paint.Style.FILL);
mDividerPaint.setColor(Color.WHITE);
}

    @Override
public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDraw(c, parent, state);
        int childCount=parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            View view=parent.getChildAt(i);
            int left=parent.getPaddingLeft();
            int right=parent.getWidth()-parent.getPaddingRight();
            int top=view.getTop()-1;
            int bottom=view.getTop();
//Item分割線
c.drawRect(left,top,right,bottom,mDividerPaint);
}
    }

    @Override
public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDrawOver(c, parent, state);
        int childCount=parent.getChildCount();
        int itemCount=state.getItemCount();
        int left=parent.getPaddingLeft();
        int right=parent.getWidth()-parent.getPaddingRight();
String preGroupTitle;
String groupTitle="";
        for (int i = 0; i < childCount; i++) {
            View child=parent.getChildAt(i);
            int pos=parent.getChildLayoutPosition(child);
preGroupTitle=groupTitle;
groupTitle=mISticky.getGroupTitle(pos);
//如果當前分組名和之前分組名一樣，忽略此次迴圈
if (groupTitle.equals(preGroupTitle)) {
                continue;
}

            //文字的基線，保證顯示完全
int textBaseLine=Math.max(mRectHeight,child.getTop());
//分組標題
String title=mISticky.getGroupTitle(pos);
            int viewBottom=child.getBottom();
//加入限定 防止陣列越界
if (pos + 1 < itemCount) {
                String nextGroupTitle=mISticky.getGroupTitle(pos+1);
//當分組不一樣  並且改組要向上移動時候
if (!nextGroupTitle.equals(groupTitle) && viewBottom < textBaseLine) {
                    //將上一個往上移動
textBaseLine = viewBottom;
}
            }
            //繪製邊框
c.drawRect(left, textBaseLine - mRectHeight, right, textBaseLine, mRectPaint);
//繪製文字並且實現文字居中
int value= (int) Math.abs(mTxtPaint.getFontMetrics().descent
+mTxtPaint.getFontMetrics().ascent);
c.drawText(title, left,
textBaseLine-(mRectHeight+value-mStatusBarHeight)/2,
mTxtPaint);
}

    }

    @Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        int pos=parent.getChildLayoutPosition(view);
        if (mISticky.isFirstPosition(pos)) {
            outRect.top=mRectHeight;
outRect.bottom=1;
}else {
            outRect.bottom=1;
}
    }
}