自定义View

LetterView.java

package com.qf.sxy.customview02;

import android.content.Context;

import android.graphics.Canvas;

import android.graphics.Color;

import android.graphics.Paint;

import android.util.AttributeSet;

import android.view.MotionEvent;

import android.view.View;

import android.widget.TextView;

/**

 * Created by sxy on 2016/9/29.

 */

public class LetterView extends View {

    // 索引的字母

    public  static final String[] LETTES ={"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 mTextPaint;

    //指定一个位置  不在索引范围内

    private int pressedPosition = -1;

    //获取展示的View

    private TextView mSelectView;

    public void setSelectTextView(TextView tv){

        this.mSelectView = tv;

    }

    public LetterView(Context context, AttributeSet attrs) {

        super(context, attrs);

        //初始化画笔

        initPaint();

    }

    private void initPaint() {

        mTextPaint = new Paint();

        mTextPaint.setAntiAlias(true);

        mTextPaint.setColor(Color.RED);

        mTextPaint.setTextSize(30);

    }

    public LetterView(Context context) {

        this(context,null);

    }

    /**

     * 进行绘制

     * @param canvas

     */

    @Override

    protected void onDraw(Canvas canvas) {

        super.onDraw(canvas);

        //获取 宽和高

        int height = getHeight();

        int width = getWidth();

        //字符串序列的长度

        int lettersLength = LETTES.length;

        //获取每个字符的高度

        int singleHeight = height/lettersLength;

        //开始绘制

        for(int i=0;i<lettersLength;i++){

            //获取x的位置

            int xPos = (int)(width/2-mTextPaint.measureText(LETTES[i])/2);

            //获取Y的位置

            int yPos = singleHeight+i*singleHeight;

            //设置文字颜色

            if(pressedPosition == i){

                mTextPaint.setColor(Color.BLUE);

            }else{

                mTextPaint.setColor(Color.BLACK);

            }

            //绘制文本

            canvas.drawText(LETTES[i],xPos,yPos,mTextPaint);

        }

    }

    /**

     * 触摸事件

     *

     * true  消费事件  false 不处理

     * @param event

     * @return

     */

    @Override

    public boolean onTouchEvent(MotionEvent event) {

        switch (event.getAction()){

            case MotionEvent.ACTION_DOWN://按下

            case MotionEvent.ACTION_MOVE://移动

                //获取手指的Y位置

                float eventY = event.getY();

                //每个字母单独的高度

                int singleHeight = getMeasuredHeight()/LETTES.length;

                //获取你当前索引位置

                pressedPosition = (int)(eventY/singleHeight);

                //显示提示的VIew  设置内容

                if(mSelectView!=null){

                    if(pressedPosition>=0&&pressedPosition<LETTES.length){

                        mSelectView.setVisibility(View.VISIBLE);

                        mSelectView.setText(LETTES[pressedPosition]);

                    }

                }

                invalidate();//刷新

                break;

            case  MotionEvent.ACTION_UP://抬起

                //还原当前位置

                pressedPosition = -1;

                //隐藏提示的View

                if (mSelectView!=null){

                    mSelectView.setVisibility(View.GONE);

                }

                invalidate();//刷新

                break;

        }

        return true;

    }

}

MainActivity.java

package com.qf.sxy.customview02;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    private TextView tv;

    private LetterView letterView;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        tv = ((TextView) findViewById(R.id.select_tv));

        letterView = ((LetterView) findViewById(R.id.letterView));

        //传递展示的View

        letterView.setSelectTextView(tv);

    }

}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:paddingBottom="@dimen/activity_vertical_margin"

    android:paddingLeft="@dimen/activity_horizontal_margin"

    android:paddingRight="@dimen/activity_horizontal_margin"

    android:paddingTop="@dimen/activity_vertical_margin"

    tools:context="com.qf.sxy.customview02.MainActivity">

    <com.qf.sxy.customview02.LetterView

        android:id="@+id/letterView"

        android:layout_width="40dp"

        android:layout_height="match_parent"

        android:layout_alignParentRight="true"

      />

    <TextView

        android:id="@+id/select_tv"

        android:layout_width="60dp"

        android:layout_height="60dp"

        android:layout_centerInParent="true"

        android:gravity="center"

        android:background="#00ff00"

        android:textSize="30sp"

        android:visibility="gone"

        android:text="A"

        />

</RelativeLayout>