如何在Android利用View模仿一个微信的LetterView效果

 public class LetterView extends View {
  private String TAG = LetterView.class.getSimpleName();
  //A,B,C....Z,#
  public List<String> letters;
  private Paint mPaint;
  private int selectPosition = -1;
  private TextView mLetter;
  public void setmLetter(TextView mLetter) {
    this.mLetter = mLetter;
  }
  public LetterView(Context context) {
    this(context,null);
  }
  public LetterView(Context context, AttributeSet attrs) {
    this(context, attrs,0);
  }
  public LetterView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    //生产字母
    letters = new ArrayList<>();
    for (int i = 65; i < 91; i++) {
      letters.add(String.format(Locale.CHINA,"%c",i));
      Log.e(TAG, "LetterView: "+ String.format(Locale.CHINA,"%c",i));
    }
    letters.add("#");//追加一个#
    //初始化画笔
    mPaint = new Paint();
    mPaint.setAntiAlias(true);
    mPaint.setColor(Color.BLUE);
    mPaint.setTextSize(30);
  }
  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    /**
     * 获取View的宽度
     * 获取View的高度
     */
    int width = getMeasuredWidth();
    int height = getMeasuredHeight();
    //测量字的宽度
    int size = letters.size();
    for (int i = 0; i < size; i++) {
      float textWidth = mPaint.measureText(letters.get(i));
      int singleHeight = height / size;
      if (selectPosition == i){//被选中的
        mPaint.setColor(Color.RED);
      }else{
        mPaint.setColor(Color.BLUE);
      }
      canvas.drawText(letters.get(i),(width - textWidth)/2, singleHeight * (i + 1),mPaint);
      /**
       * drawText() x y \_ 为基准线
       */
    invalidate();
    }
  }
  /**
   * Android将触摸事件封装,包装了动作,位置信息;onClick也是一种motionEvent
   * onClick 事件 实际上是 onTouchEvent事件
   * @param event
   * @return
   */
  @Override
  public boolean onTouchEvent(MotionEvent event) {
    //包装了动作,位置信息
//    event.getY();//相对于View本身的坐标值
//    event.getRawY();//返回的是相对于屏幕的坐标值
    float y = event.getY();
    Log.e(TAG, "onTouchEvent: Y:"+ y);
//    Log.e(TAG, "onTouchEvent: RawY:"+event.getRawY() );
    int measuredHeight = getMeasuredHeight();
    int singleHeight = measuredHeight / letters.size();
    int position = (int) (y / singleHeight);
    Log.e(TAG, "onTouchEvent: " + position );
    switch (event.getAction()) {
      case MotionEvent.ACTION_MOVE:
        Log.e(TAG, "onTouchEvent: ACTION_MOVE" );
      case MotionEvent.ACTION_DOWN:
        Log.e(TAG, "onTouchEvent: ACTION_DOWN" );
        selectPosition = position;
        if (mLetter != null) {
          mLetter.setVisibility(View.VISIBLE);
          //极限情况有可能下标越界,需要判断一下
          if (position < letters.size() && position >= 0){
            mLetter.setText(letters.get(position));
          }
        }
        break;
      case MotionEvent.ACTION_UP:
        Log.e(TAG, "onTouchEvent: ACTION_UP" );
        selectPosition = -1;
        if (mLetter != null) {
          mLetter.setVisibility(View.GONE);
        }
        break;
    }
    //返回true代表事件被处理了
    return true;
  }
}