<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.example.datepicker.MainActivity" >

 <TextView
  android:id="@+id/editText"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_centerHorizontal="true"
  android:layout_centerVertical="true"
  android:hint="選擇你的出生年月" />

 <Button
  android:id="@+id/select"
  android:onClick="SelectAge"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_alignBaseline="@+id/editText"
  android:layout_alignBottom="@+id/editText"
  android:layout_alignParentLeft="true"
  android:text="選擇年齡" />

</RelativeLayout>

package com.example.datepicker;

import java.text.SimpleDateFormat;
import java.util.Date;

import android.app.Activity;
import android.app.DatePickerDialog;
import android.app.DatePickerDialog.OnDateSetListener;
import android.os.Bundle;
import android.view.View;

import android.view.Window;
import android.widget.DatePicker;

import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity implements OnDateSetListener {
 private TextView mText;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  requestWindowFeature(Window.FEATURE_NO_TITLE);
  setContentView(R.layout.activity_main);
  mText = (TextView) findViewById(R.id.editText);
 }

 public void SelectAge(View v) {
// 這設置默認顯示的日期 我選的2000年1月1日       月這是從0開始 0 是一月
  new DatePickerDialog(MainActivity.this, this, 2000, 0, 1).show();

 }

 @Override
 public void onDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth) {
  // TODO Auto-generated method stub
//  選擇1月會是0 要把月份+1
  Toast.makeText(MainActivity.this, "你選擇的是" + year + "年" + (monthOfYear+1) + "月" + dayOfMonth + "日",
    Toast.LENGTH_LONG).show();
  SimpleDateFormat format = new SimpleDateFormat("yyyy");
  int NowYear = Integer.parseInt(format.format(new Date()));
  mText.setText("你今年" + (NowYear - year) + "歲");

 }

}