Android ListView右侧的字母索引View

public class SideBar extends View {

   public static String[] INDEX_STRING = { "","#", "","","A", "B", "C", "D", "E", "F", "G", 
      "","H",  "I", "J", "K", "L", "M", "N",
                                            "","O",  "P", "Q", "","R", "S", "T", 
                                            "","U", "V",  "", "W", "X",  "",  "Y", 
                                            "","Z" };

   // public static String[] INDEX_SHOW = { "#", "A", ".", ".", ".", ".", "F",
   // ".", ".", ".", ".", "K", ".", ".", ".", ".", "P", ".", ".", ".",
   // ".", "U", ".", ".", ".", ".", "Z" };

   public static String[] INDEX_SHOW = { "","#","","", 
                               "A", "","", ".", ".", "", "",
                               "","H", "", "", ".", ".", "", "", 
                               "","O", "","", ".", ".", "", "", 
                               "","U", "", "",".", ".", "", "",
                               "","Z" };

   private OnTouchingLetterChangedListener onTouchingLetterChangedListener;
   private List letterList;
   private List letterShow;
   private int choose = -1;
   private Paint paint = new Paint();
   private TextView mTextDialog;

   public SideBar(Context context) {
      this(context, null);
   }

   public SideBar(Context context, AttributeSet attrs) {
      this(context, attrs, 0);
   }

   public SideBar(Context context, AttributeSet attrs, int defStyle) {
      super(context, attrs, defStyle);
      init();
   }

   private void init() {
      setBackgroundColor(Color.parseColor("#00000000"));
      letterList = Arrays.asList(INDEX_STRING);
      letterShow = Arrays.asList(INDEX_SHOW);
   }

   protected void onDraw(Canvas canvas) {
      super.onDraw(canvas);
      int height = getHeight();// 获取对应高度
      int width = getWidth();// 获取对应宽度
      int singleHeight = height / letterShow.size();// 获取每一个字母的高度
      for (int i = 0; i < letterShow.size(); i++) {
         paint.setColor(Color.parseColor("#FFFFFF"));
         paint.setTypeface(Typeface.DEFAULT_BOLD);
         paint.setAntiAlias(true);
         paint.setTextSize(26);
         // 选中的状态
         if (i == choose) {
            paint.setColor(Color.parseColor("#4F41FD"));
            paint.setTextSize(28);
            paint.setFakeBoldText(true);
         }
         // x坐标等于中间-字符串宽度的一半.
         float xPos = width / 2 - paint.measureText(letterShow.get(i)) / 2;
         float yPos = singleHeight * i + singleHeight -2;
         canvas.drawText(letterShow.get(i), xPos, yPos, paint);
         paint.reset();// 重置画笔
      }
   }

   @Override
   public boolean dispatchTouchEvent(MotionEvent event) {
      final int action = event.getAction();
      final float y = event.getY();// 点击y坐标
      final int oldChoose = choose;
      final OnTouchingLetterChangedListener listener = onTouchingLetterChangedListener;
      final int c = (int) (y / getHeight() * letterShow.size());// 点击y坐标所占总高度的比例*b数组的长度就等于点击b中的个数.

      switch (action) {
      case MotionEvent.ACTION_UP:
         setBackgroundColor(Color.parseColor("#00000000"));
         choose = -1;
         invalidate();
         if (mTextDialog != null) {
            mTextDialog.setVisibility(View.GONE);
         }
         break;
      default:
         setBackgroundColor(Color.parseColor("#00000000"));
         if (oldChoose != c) {
            if (c >= 0 && c < letterList.size()) {
               String alertText = letterList.get(c);
               if (listener != null && !"".equals(alertText)) {
                  listener.onTouchingLetterChanged(alertText);
               }
               if (mTextDialog != null && !"".equals(alertText)) {
                  mTextDialog.setText(alertText);
                  mTextDialog.setVisibility(View.VISIBLE);
               }
               choose = c;
               invalidate();
            }
         }
         break;
      }
      return true;
   }

   public void setIndexText(ArrayList indexStrings) {
      this.letterList = indexStrings;
      invalidate();
   }

   /**
    * 为SideBar设置显示当前按下的字母的TextView
    *
    * @param mTextDialog
    */
   public void setTextView(TextView mTextDialog) {
      this.mTextDialog = mTextDialog;
   }

   /**
    * 向外公开的方法
    *
    * @param onTouchingLetterChangedListener
    */
   public void setOnTouchingLetterChangedListener(OnTouchingLetterChangedListener onTouchingLetterChangedListener) {
      this.onTouchingLetterChangedListener = onTouchingLetterChangedListener;
   }

   /**
    * 接口
    */
   public interface OnTouchingLetterChangedListener {
      void onTouchingLetterChanged(String s);
   }

}