参考文章

1. Android使用RecycleView实现魅族手机通讯录界面
2. Android微信通讯录滑动快速定位实现
3. 更快实现Android多级树形选择列表
4. 其中recyclerview部分参考第一篇文章，侧边栏参考第二篇文章

关键点：

1. 判断是否分组的开始

2. ItemDecoration

   1. getItemOffsets为绘制分组头部字母和分割线预留空间
   2. onDraw绘制分组头部字母
   3. onDrawOver绘制悬停字母

3. 侧边栏的实现

   1. 侧边栏的事件

效果如下

关键代码

1. 关键点1代码

   /**
    * 是否是分组头部 当前位置和上一个位置的首字母不一样，则是分组的头部
    * @param position 位置
    * @return
    */
   private boolean isSectionHeader(int position){
       if (position == 0){
           return true;
       }else{
           if (!modelList.get(position).getIndexTag().equals(modelList.get(position - 1).getIndexTag())){
               return true;
           }else {
               return false;
           }
       }
   }
   

2. 关键点2代码

    @Override
    public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        //parent.getChildLayoutPosition(view); 区别
        int position = parent.getChildAdapterPosition(view);
        if (modelList == null || modelList.size() == 0 || modelList.size() <= position || position < 0) {
            super.getItemOffsets(outRect, view, parent, state);
            return;
        }
        if (isSectionHeader(position)){
            outRect.top = dividerHeight;
        }else {
            outRect.top = 1;
        }
    }
   
       @Override
       public void onDraw(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
           int count = parent.getChildCount();
           for (int i = 0; i < count; i++) {
               View view = parent.getChildAt(i);
               int position = parent.getChildAdapterPosition(view);
               //考虑到recyclerview的内边距
               int left = parent.getPaddingLeft();
               int right = parent.getWidth() - parent.getPaddingRight();//?parent.getRight - parent.getPaddingRight()
               if (isSectionHeader(position)){//分组头部
                   //1.先画矩形
   //                c.drawRect(0,view.getTop() - dividerHeight,right,view.getTop(),mPaint);
                   //2.画圆
                   //改变画笔的颜色
   //                ColorUtil.setPaintColor(mPaint,tagsStr.indexOf(modelList.get(position).getIndexTag()));
   //                c.drawCircle(QMUIDisplayHelper.dp2px(mContext, 42), view.getTop() - dividerHeight / 2, 35, mPaint);
                   //3.画字
                   mPaint.setTextSize(40);
                   mPaint.setColor(Color.parseColor("#909090"));
                   c.drawText(modelList.get(position).getFirstLetter(),QMUIDisplayHelper.dp2px(mContext,42),view.getTop()-dividerHeight/3,mPaint);
               }else {//普通item
   //                c.drawRect(0,view.getTop() - 1,right,view.getTop(),linePaint);
   //                c.drawLine(0,view.getTop() - 1,right,view.getTop(),linePaint);//画分割线,宽度不会撑满
               }
           }
       }
   
   
       @Override
       public void onDrawOver(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
           //第一个可见的item的position
           int position = ((LinearLayoutManager) (parent.getLayoutManager())).findFirstVisibleItemPosition();
           if (modelList == null || modelList.size() == 0 || modelList.size() <= position || position < 0){
               return;
           }
           int bottom = parent.getPaddingTop() + dividerHeight;
           mPaint.setColor(Color.parseColor("#ffffff"));
           c.drawRect(parent.getLeft(), parent.getPaddingTop(), parent.getRight() - parent.getPaddingRight(), parent.getPaddingTop() + dividerHeight, mPaint);
   //        ColorUtil.setPaintColor(mPaint, tagsStr.indexOf(modelList.get(position).getIndexTag()));
   //        c.drawCircle(QMUIDisplayHelper.dp2px(mContext, 42), bottom - dividerHeight / 2, 35, mPaint);
           mPaint.setTextSize(40);
           mPaint.setColor(Color.parseColor("#007aff"));
           c.drawText(modelList.get(position).getFirstLetter(), QMUIDisplayHelper.dp2px(mContext, 42), bottom - dividerHeight / 3, mPaint);
       }
   
   

3. 关键点3代码

   @Override
   public boolean onTouchEvent(MotionEvent event) {
       switch (event.getAction()) {
           case MotionEvent.ACTION_DOWN:
               setBackgroundColor(TOUCHED_BACKGROUND_COLOR);
               handle(event);
               return true;
           case MotionEvent.ACTION_MOVE:
               handle(event);
               return true;
           case MotionEvent.ACTION_UP:
           case MotionEvent.ACTION_CANCEL:
               setBackgroundColor(Color.TRANSPARENT);
               handle(event);
               return true;
       }
       return super.onTouchEvent(event);
   }
   
       private void handle(MotionEvent event) {
   
           int color =  downTextColor;
           if (event.getAction() == MotionEvent.ACTION_UP){
               color = indexTextColor;
           }
           for (int i = 0; i < getChildCount(); i++) {
               View vi = getChildAt(i);
               if (vi instanceof TextView){
                   ((TextView) vi).setTextColor(color);
               }
           }
   
           int y = (int) event.getY();
           int height = getHeight();
           //触摸点的距离除以每个字母的高度(控件高度除以字母的个数)
           int position =  y / (height/INDEXES.length);
           if (position < 0){
               position = 0;
           }else if (position >= INDEXES.length){
               position = INDEXES.length - 1;
           }
           String tag = INDEXES[position];
           boolean showInicator = event.getAction() != MotionEvent.ACTION_UP && event.getAction() != MotionEvent.ACTION_CANCEL;
           if (listener != null){
               listener.onIndexChanged(tag,position, showInicator);
           }
       }
   

完整代码github