自定义一个字母Button

 package com.example.administrator.yunstore.widget;

 import android.content.Context;
 import android.graphics.Canvas;
 import android.graphics.Color;
 import android.graphics.Paint;
 import android.graphics.Typeface;
 import android.util.AttributeSet;
 import android.view.MotionEvent;
 import android.widget.Button;

 /**
  * Created by Administrator on 2016/10/19.
  * 自定义的一个字母button
  */

 public class LetterButton extends Button {

     // 分类字母
     private String[] assort = { "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" };

     private Paint paint = new Paint();

     private int selectIndex = -1;

     public LetterButton(Context context) {
         super(context);
     }

     public LetterButton(Context context, AttributeSet attrs) {
         super(context, attrs);
     }

     public LetterButton(Context context, AttributeSet attrs, int defStyleAttr) {
         super(context, attrs, defStyleAttr);
     }

     /**
      * @param canvas
      * 对按钮进行绘制
      */
     @Override
     protected void onDraw(Canvas canvas) {
         super.onDraw(canvas);

         int height=getHeight();
         int width=getWidth();
         int interval = height / assort.length;

         for (int i = 0, length = assort.length; i < length; i++) {
             // 抗锯齿
             paint.setAntiAlias(true);
             // 默认粗体
             paint.setTypeface(Typeface.DEFAULT_BOLD);
             // 白色
             paint.setColor(Color.BLUE);
             if (i == selectIndex) {
                 // 被选择的字母改变颜色和粗体
                 paint.setColor(Color.parseColor("#33bb99"));
                 paint.setFakeBoldText(true);
                 paint.setTextSize(30);
             }
             // 计算字母的X坐标
             float xPos = width / 2 - paint.measureText(assort[i]) / 2;
             // 计算字母的Y坐标
             float yPos = interval * i + interval;
             canvas.drawText(assort[i], xPos, yPos, paint);
             paint.reset();
         }
     }

     @Override
     public boolean dispatchTouchEvent(MotionEvent event) {
         float y = event.getY();
         int index = (int) (y / getHeight() * assort.length);
         if (index >= 0 && index < assort.length) {

             switch (event.getAction()) {
                 case MotionEvent.ACTION_MOVE:
                     // 如果滑动改变
                     if (selectIndex != index) {
                         selectIndex = index;
                         if (onTouch != null) {
                             onTouch.onTouchAssortListener(assort[selectIndex]);
                         }

                     }
                     break;
                 case MotionEvent.ACTION_DOWN:
                     selectIndex = index;
                     if (onTouch != null) {
                         onTouch.onTouchAssortListener(assort[selectIndex]);
                     }

                     break;
                 case MotionEvent.ACTION_UP:
                     if (onTouch != null) {
                         onTouch.onTouchAssortUP();
                     }
                     selectIndex = -1;
                     break;
             }
         } else {
             selectIndex = -1;
             if (onTouch != null) {
                 onTouch.onTouchAssortUP();
             }
         }
         invalidate();

         return true;
     }

     @Override
     public boolean onTouchEvent(MotionEvent event) {
         return super.onTouchEvent(event);
     }
     //字母监听器
     private OnTouchAssortListener onTouch;

     public interface OnTouchAssortListener {
          void onTouchAssortListener(String s);
           void onTouchAssortUP();
     }

     public void setOnTouchAssortListener(OnTouchAssortListener onTouch) {
         this.onTouch = onTouch;
     }
 }