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);        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);          invalidate();    }  }    @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;  }}