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;
    }
}