Android之怎么使用SQLite数据库(增、删、改、查、分页等)以及ListView显示数据

xuxiaohui9216

由于刚接触android开发，故此想把学到的基础知识记录一下，以备查询，故此写的比较啰嗦：
步骤如下：
一、介绍：
此文主要是介绍怎么使用android自带的数据库SQLite，以及把后台的数据用ListView控件显示
二、新建一个android工程——DBSQLiteOperate
工程目录：

三、清单列表AndroidManifest.xml的配置为：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.dboperate"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk android:minSdkVersion="8" />
<application
android:icon="@drawable/ic_launcher"
android:label="@string/app_name" >

<!--单元测试 加这句-->
<uses-library android:name="android.test.runner" />

<activity
android:name=".DBSQLiteOperateActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
<instrumentation android:name="android.test.InstrumentationTestRunner"
android:targetPackage="com.example.dboperate"
android:label="Test for my app"/>
</manifest>
四、main.xml配置清单：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<LinearLayout android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<TextView
android:id="@+id/name"
android:layout_width="100dip"
android:layout_height="wrap_content"
android:text="@string/name"
android:gravity="center"/>
<TextView
android:id="@+id/phone"
android:layout_width="100dip"
android:layout_height="wrap_content"
android:text="@string/phone"
android:gravity="center"/>
<TextView
android:id="@+id/amount"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/amount"
android:gravity="center"/>
</LinearLayout>
<ListView
android:id="@+id/listView"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
</ListView>
</LinearLayout>
五、item.xml配置清单：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal" >
<TextView
android:id="@+id/name"
android:layout_width="100dip"
android:layout_height="wrap_content"
android:text="@string/name"
android:gravity="center"/>
<TextView
android:id="@+id/phone"
android:layout_width="100dip"
android:layout_height="wrap_content"
android:text="@string/phone"
android:gravity="center"/>
<TextView
android:id="@+id/amount"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/amount"
android:gravity="center"/>
</LinearLayout>
六、string.xml配置清单：
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="hello">Hello World, DBSQLiteOperateActivity!</string>
<string name="app_name">ExampleDBSQLiteOperate8</string>
<string name="name">姓名</string>
<string name="phone">电话</string>
<string name="amount">存款</string>
</resources>
七、DBSQLiteOperateActivity.java Activity类的源码：
package com.example.dboperate;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import com.example.adapter.PersonAdapter;
import com.example.domain.Person;
import com.example.service.PersonService;
import android.app.Activity;
import android.database.Cursor;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.SimpleCursorAdapter;
import android.widget.Toast;
public class DBSQLiteOperateActivity extends Activity {

ListView listView;
PersonService personService;
OnItemClickListener listViewListener;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

listViewListener = new OnItemClickListener(){

@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
//得到listView控件
ListView listView = (ListView)parent;

//1、如果使用自定义适配器，返回的是Person对象
//得到该条目数据
//Person person = (Person)listView.getItemAtPosition(position);
////广播出去
//Toast.makeText(getApplicationContext(), person.toString(), Toast.LENGTH_LONG).show();

//2、如果使用showList2()方法中的适配器时，则取得的值是不一样的,返回的是cursor
//Cursor cursor = (Cursor)listView.getItemAtPosition(position);
//int personid = cursor.getInt(cursor.getColumnIndex("_id"));
//Toast.makeText(getApplicationContext(), personid+"", Toast.LENGTH_LONG).show();

//3、如果使用showList()方法中的适配器时，则取得的值是不一样的,返回的是map
@SuppressWarnings("unchecked")
Map<String,Object> map = (Map)listView.getItemAtPosition(position);
String name = map.get("name").toString();
String personid = map.get("personid").toString();
Toast.makeText(getApplicationContext(), personid +"-"+ name, Toast.LENGTH_LONG).show();

}

};

listView = (ListView) this.findViewById(R.id.listView);
listView.setOnItemClickListener(listViewListener);
personService = new PersonService(this);
showList();
}
private void showList() {
List<Person> persons = personService.getScrollData(0, 50);
List<HashMap<String,Object>> data = new ArrayList<HashMap<String,Object>>();
for(Person person : persons){
HashMap<String,Object> item = new HashMap<String,Object>();
item.put("name", person.getName());
item.put("phone", person.getPhone());
item.put("amount", person.getAmount());
item.put("personid", person.getId());
data.add(item);
}
SimpleAdapter adapter = new SimpleAdapter(this,data,R.layout.item, new String[]{"name","phone","amount"}, new int[]{R.id.name,R.id.phone,R.id.amount});
listView.setAdapter(adapter);
}

public void showList2(){
Cursor cursor = personService.getCursorScrollData(0, 50);
//该适配器要求返回的结果集cursor必须包含_id字段，所以需要对取得结果集进行处理
SimpleCursorAdapter adapter = new SimpleCursorAdapter(this,R.layout.item,cursor,new String[]{"name","phone","amount"}, new int[]{R.id.name,R.id.phone,R.id.amount} );
listView.setAdapter(adapter);
}
/**
* 自定义适配器
*/
public void showList3(){
List<Person> persons = personService.getScrollData(0, 50);
/**
* 第一个参数：上下文context，第二个参数：要显示的数据，第三个参数：绑定的条目界面
*/
PersonAdapter adapter = new PersonAdapter(this, persons, R.layout.item);
listView.setAdapter(adapter);
}
}
八、person.java 实体类 源码：
package com.example.domain;
public class Person {
private Integer id;
private String name;
private String phone;
private Integer amount;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPhone() {
return phone;
}
public void setPhone(String phone) {
this.phone = phone;
}

public Person(String name, String phone) {
this.name = name;
this.phone = phone;
}
public Person(Integer id, String name, String phone,Integer amount) {
super();
this.id = id;
this.name = name;
this.phone = phone;
this.amount = amount;
}
public Person() {
super();
}
public Integer getAmount() {
return amount;
}
public void setAmount(Integer amount) {
this.amount = amount;
}
@Override
public String toString() {
return "Person [id=" + id + ", name=" + name + ", phone=" + phone
+ ", amount=" + amount + "]";
}


}

九、DBOperateHelper.java 业务类源码：
package com.example.service;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
public class DBOperateHelper extends SQLiteOpenHelper {
public DBOperateHelper(Context context) {//默认创建的数据库文件保存在<包名>/database/
//第一个参数是上下文，第二个参数是数据库名称，第三个是游标工厂为null时使用 数据库默认的游标工厂,第四个是数据库版本号但是不能为0，一般大于0
super(context, "smallpig", null, 4);
}
/**
* 数据库每一次被创建时被调用
*/
@Override
public void onCreate(SQLiteDatabase sqldb) {
sqldb.execSQL("create table person(personid integer primary key autoincrement,name varchar(20),phone varchar(12) null)");

}
/**
* 每一次数据库版本号发生变动时触发此方法
* 比如如果想往数据库中再插入一些表、字段或者其他信息时通过修改数据库版本号来触发此方法
*/
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
//db.execSQL("alter table person add phone varchar(12) null");\
db.execSQL("alter table person add amount Integer null");
}
}

十、PersonService.java 业务类源码：
package com.example.service;
import java.util.ArrayList;
import java.util.List;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import com.example.domain.Person;
public class PersonService {
private DBOperateHelper dbOperateHelper;

public PersonService(Context context) {
this.dbOperateHelper = new DBOperateHelper(context);
}
/**
* 保存记录
* @param person
*/
public void save(Person person){
//得到数据库实例，里面封装了数据库操作方法
SQLiteDatabase sqldb = dbOperateHelper.getWritableDatabase();
//sqldb.execSQL("insert into person(name,phone) values('"+person.getName()+"','"+person.getPhone()+"')");
//利用占位符可以避免注入，但是注意数组参与与占位符对应的字段要一一对应
sqldb.execSQL("insert into person(name,phone,amount) values(?,?,?)",new Object[]{person.getName(),person.getPhone(),person.getAmount()});
//关闭数据库
sqldb.close();
}

/**
* 删除记录
* @param id
*/
public void delete(Integer id){
SQLiteDatabase sqldb = dbOperateHelper.getWritableDatabase();
sqldb.execSQL("delete from person where personid=?",new Object[]{id});
sqldb.close();
}

/**
* 更新记录
* @param person
*/
public void update(Person person){
SQLiteDatabase sqldb = dbOperateHelper.getWritableDatabase();
sqldb.execSQL("update person set name=?,phone=?,amount=? where personid=?",new Object[]{person.getName(),person.getPhone(),person.getAmount(),person.getId()});
sqldb.close();
}

/**
* 通过ID查询记录
* @param id
* @return
*/
public Person find(Integer id){
/**
* getWritableDatabase 与 getReadableDatabase 的区别：
* getReadableDatabase会先返回getWritableDatabase(可写)，如果调用getWritableDatabase失败
* 则才会调用getReadableDatabase后续方法，使数据库只读
* 当写入的数据超过数据库大小则调用getWritableDatabase会失败
* 所以只读时则可以使用此方法，其它情况(只要不是超过数据库大小)也可以使用此方法
*/
SQLiteDatabase sqldb = dbOperateHelper.getReadableDatabase();
Cursor cursor = sqldb.rawQuery("select * from person where personid=?", new String[]{String.valueOf(id)});
int personid;
String name;
String phone;
int amount;
Person person = null;
if(cursor.moveToFirst()){
personid = cursor.getInt(cursor.getColumnIndex("personid"));
name = cursor.getString(cursor.getColumnIndex("name"));
phone = cursor.getString(cursor.getColumnIndex("phone"));
amount = cursor.getInt(cursor.getColumnIndex("amount"));
person = new Person(personid,name,phone,amount);
}
cursor.close();
return person;
}

/**
* 返回指定长度记录，limit 3,5,适用于分页
* @param offset 起始
* @param maxResult 长度
* @return
*/
public List<Person> getScrollData(int offset,int maxResult){

SQLiteDatabase sqldb = dbOperateHelper.getReadableDatabase();
Cursor cursor = sqldb.rawQuery("select * from person order by personid asc limit ?,?", new String[]{String.valueOf(offset),String.valueOf(maxResult)});
int personid;
String name;
String phone;
int amount;
Person person = null;
List<Person> persons = new ArrayList<Person>();
while(cursor.moveToNext()){
personid = cursor.getInt(cursor.getColumnIndex("personid"));
name = cursor.getString(cursor.getColumnIndex("name"));
phone = cursor.getString(cursor.getColumnIndex("phone"));
amount = cursor.getInt(cursor.getColumnIndex("amount"));
person = new Person(personid,name,phone,amount);
persons.add(person);
}
cursor.close();
return persons;
}

/**
* 返回cursor
* @param offset 起始
* @param maxResult 长度
* @return
*/
public Cursor getCursorScrollData(int offset,int maxResult){

SQLiteDatabase sqldb = dbOperateHelper.getReadableDatabase();
Cursor cursor = sqldb.rawQuery("select personid as _id,name,phone,amount from person order by personid asc limit ?,?", new String[]{String.valueOf(offset),String.valueOf(maxResult)});

return cursor;
}

/**
* 返回总记录数
* @return
*/
public long getCount(){
SQLiteDatabase sqldb = dbOperateHelper.getReadableDatabase();

Cursor cursor = sqldb.rawQuery("select count(*) from person", null);
//该查询语句值返回一条语句
cursor.moveToFirst();
long result = cursor.getLong(0);
cursor.close();
return result;
}

public void payment(){
SQLiteDatabase sqldb = dbOperateHelper.getWritableDatabase();
sqldb.beginTransaction();//开启事务
try{
sqldb.execSQL("update person set amount = amount -10 where personid=1");
sqldb.execSQL("update person set amount = amount + 10 where personid=2");
sqldb.setTransactionSuccessful();//设置事务标志位true
} finally {
//结束事务：有两种情况：commit\rollback，事务提交或者回滚是由事务的标识决定的
//事务为ture则提交，事务为flase则回滚，默认为false
sqldb.endTransaction();
}
}
}

十一、OtherPersonService.java 业务类源码：
package com.example.service;
import java.util.ArrayList;
import java.util.List;
import com.example.domain.Person;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
public class OtherPersonService {

private DBOperateHelper dbOperateHelper;

public OtherPersonService(Context context) {
this.dbOperateHelper = new DBOperateHelper(context);
}
/**
* 保存记录
* @param person
*/
public void save(Person person){
//得到数据库实例，里面封装了数据库操作方法
SQLiteDatabase sqldb = dbOperateHelper.getWritableDatabase();
//sqldb.execSQL("insert into person(name,phone) values('"+person.getName()+"','"+person.getPhone()+"')");
//利用占位符可以避免注入，但是注意数组参与与占位符对应的字段要一一对应
//sqldb.execSQL("insert into person(name,phone) values(?,?)",new Object[]{person.getName(),person.getPhone()});

ContentValues values = new ContentValues();
values.put("name", person.getName());
values.put("phone", person.getPhone());
values.put("amount", person.getAmount());
//第一个参数是表名，第三个为字段值集合，第二个参数是空值字段，当第三个字段值集合为空时，系统会自动插入一条第二个参数为空的sql语句
//否则当第三个参数为空时，如果第二个参数也为空，那么插入表就会找不到插入的字段信息，会报错
sqldb.insert("person", "name", values );
//关闭数据库
sqldb.close();
}

/**
* 删除记录
* @param id
*/
public void delete(Integer id){
SQLiteDatabase sqldb = dbOperateHelper.getWritableDatabase();
//sqldb.execSQL("delete from person where personid=?",new Object[]{id});
//第一个参数是表名，第二个是where后面的条件用占位符表示，第三个对应占位符为参数值
sqldb.delete("person", "personid=?", new String[]{Integer.toString(id)});
sqldb.close();
}

/**
* 更新记录
* @param person
*/
public void update(Person person){
SQLiteDatabase sqldb = dbOperateHelper.getWritableDatabase();
//sqldb.execSQL("update person set name=?,phone=? where personid=?",new Object[]{person.getName(),person.getPhone(),person.getId()});
//第一个参数为表名，第二个是一个更新值集合，采用键值对的形式，每个更新的字段对应更新值
//第三个参数是where后面条件字段用占位符标识，第四个参数是对应where占位符的值
ContentValues values = new ContentValues();
values.put("name", person.getName());
values.put("phone", person.getPhone());
values.put("amount", person.getAmount());
sqldb.update("person", values , "personid=?", new String[]{person.getId().toString()});
sqldb.close();
}

/**
* 通过ID查询记录
* @param id
* @return
*/
public Person find(Integer id){
/**
* getWritableDatabase 与 getReadableDatabase 的区别：
* getReadableDatabase会先返回getWritableDatabase(可写)，如果调用getWritableDatabase失败
* 则才会调用getReadableDatabase后续方法，使数据库只读
* 当写入的数据超过数据库大小则调用getWritableDatabase会失败
* 所以只读时则可以使用此方法，其它情况(只要不是超过数据库大小)也可以使用此方法
*/
SQLiteDatabase sqldb = dbOperateHelper.getReadableDatabase();
//Cursor cursor = sqldb.rawQuery("select * from person where personid=?", new String[]{String.valueOf(id)});
//第一个参数是表名；第二个参数是查询显示的字段，null时默认查询显示所有字段；
//第三个参数是where查询条件占位符；第四个是占位符对应的值；
//第五个参数是group by条件；第六个是having条件；第七个是order by条件
Cursor cursor = sqldb.query("person", null, "personid=?", new String[]{id.toString()}, null, null, null);
int personid;
String name;
String phone;
int amount;
Person person = null;
if(cursor.moveToFirst()){
personid = cursor.getInt(cursor.getColumnIndex("personid"));
name = cursor.getString(cursor.getColumnIndex("name"));
phone = cursor.getString(cursor.getColumnIndex("phone"));
amount = cursor.getInt(cursor.getColumnIndex("amount"));
person = new Person(personid,name,phone,amount);
}
cursor.close();
return person;
}

/**
* 返回指定长度记录，limit 3,5,适用于分页
* @param offset 起始
* @param maxResult 长度
* @return
*/
public List<Person> getScrollData(int offset,int maxResult){

SQLiteDatabase sqldb = dbOperateHelper.getReadableDatabase();
//Cursor cursor = sqldb.rawQuery("select * from person order by personid asc limit ?,?", new String[]{String.valueOf(offset),String.valueOf(maxResult)});
//第一个参数是表名；第二个参数是查询显示的字段，null时默认查询显示所有字段；
//第三个参数是where查询条件占位符；第四个是占位符对应的值；
//第五个参数是group by条件；第六个是having条件；第七个是order by条件
//第八个参数是limit ?,? 条件
Cursor cursor = sqldb.query("person", null, null, null, null, null, "personid",offset+","+maxResult);

int personid;
String name;
String phone;
int amount;
Person person = null;
List<Person> persons = new ArrayList<Person>();
while(cursor.moveToNext()){
personid = cursor.getInt(cursor.getColumnIndex("personid"));
name = cursor.getString(cursor.getColumnIndex("name"));
phone = cursor.getString(cursor.getColumnIndex("phone"));
amount = cursor.getInt(cursor.getColumnIndex("amount"));
person = new Person(personid,name,phone,amount);
persons.add(person);
}
cursor.close();
return persons;
}

/**
* 返回总记录数
* @return
*/
public long getCount(){
SQLiteDatabase sqldb = dbOperateHelper.getReadableDatabase();
//Cursor cursor = sqldb.rawQuery("select count(*) from person", null);
//第一个参数是表名；第二个参数是查询显示的字段，null时默认查询显示所有字段；
//第三个参数是where查询条件占位符；第四个是占位符对应的值；
//第五个参数是group by条件；第六个是having条件；第七个是order by条件
Cursor cursor = sqldb.query("person", new String[]{"count(*)"}, null, null, null, null, null);
//该查询语句值返回一条语句
cursor.moveToFirst();
long result = cursor.getLong(0);
cursor.close();
return result;
}
}

十二、PersonServiceTest.java 单元测试类源码：
package com.example.test;
import java.util.List;
import com.example.domain.Person;
import com.example.service.DBOperateHelper;
import com.example.service.PersonService;import android.test.AndroidTestCase;
import android.util.Log;
public class PersonServiceTest extends AndroidTestCase {
public void testCreateDB() throws Exception{
DBOperateHelper dbHelper = new DBOperateHelper(getContext());
dbHelper.getWritableDatabase();
}
public void testSave() throws Exception{
PersonService ps = new PersonService(getContext());
for(int i=1;i<=100;i++){
Person person = new Person();
person.setName("我是"+i);
person.setPhone(String.valueOf(Long.parseLong("18888888800")+i));
ps.save(person);
Log.i("PersonService",person.toString());
}
}
public void testDelete() throws Exception{
PersonService ps = new PersonService(getContext());
ps.delete(10);
}
public void testUpdate() throws Exception{
PersonService ps = new PersonService(getContext());
ps.update(new Person(1,"xiaopang","18887654321",0));
}
public void testFind() throws Exception{
PersonService ps = new PersonService(getContext());
Person person = ps.find(1);
Log.i("PersonService", person.toString());
}
public void testGetScrollData() throws Exception{
PersonService ps = new PersonService(getContext());
List<Person> persons = ps.getScrollData(3, 5);
for(Person person:persons){
Log.i("PersonService",person.toString());
}
}
public void testGetCount() throws Exception{
PersonService ps = new PersonService(getContext());
Long count = ps.getCount();
Log.i("PersonService",count.toString());
}
public void testUpdateAmount() throws Exception{
PersonService ps = new PersonService(getContext());
Person person1 = ps.find(1);
Person person2 = ps.find(2);
person1.setAmount(100);
person2.setAmount(100);
ps.update(person1);
ps.update(person2);
}
public void testPayment() throws Exception{
PersonService ps = new PersonService(getContext());
ps.payment();
}
}
十三、OtherPersonServiceTest 单元测试类源码：
package com.example.test;
import java.util.List;
import com.example.domain.Person;
import com.example.service.DBOperateHelper;
import com.example.service.OtherPersonService;
import android.test.AndroidTestCase;
import android.util.Log;
public class OtherPersonServiceTest extends AndroidTestCase {
public void testCreateDB() throws Exception{
DBOperateHelper dbHelper = new DBOperateHelper(getContext());
dbHelper.getWritableDatabase();
}
public void testSave() throws Exception{
OtherPersonService ps = new OtherPersonService(getContext());
for(int i=1;i<=100;i++){
Person person = new Person();
person.setName("我是"+i);
person.setPhone(String.valueOf(Long.parseLong("18888888800")+i));
ps.save(person);
Log.i("PersonService",person.toString());
}
}
public void testDelete() throws Exception{
OtherPersonService ps = new OtherPersonService(getContext());
ps.delete(10);
}
public void testUpdate() throws Exception{
OtherPersonService ps = new OtherPersonService(getContext());
ps.update(new Person(1,"xiaopang","18887654321",0));
}
public void testFind() throws Exception{
OtherPersonService ps = new OtherPersonService(getContext());
Person person = ps.find(1);
Log.i("PersonService", person.toString());
}
public void testGetScrollData() throws Exception{
OtherPersonService ps = new OtherPersonService(getContext());
List<Person> persons = ps.getScrollData(3, 5);
for(Person person:persons){
Log.i("PersonService",person.toString());
}
}
public void testGetCount() throws Exception{
OtherPersonService ps = new OtherPersonService(getContext());
Long count = ps.getCount();
Log.i("PersonService",count.toString());
}
}
十四、注意事项以及相关知识点：
1、掌握SQLite数据库如何创建数据库、建立表、维护字段等操作
继承SQLiteOpenHelper类，构造函数调用父类构造函数创建数据库，利用onCreate创建表，利用onUpgrade更新表字段信息
2、掌握SQLite数据库如何增、删、改、查以及分页
取得SQLiteDatabase的实例，然后调用该实例的方法可以完成上述操作
SQLiteDataBase提供两种操作上述功能的方式：一是直接调用execSQL书写sql语句，另一种是通过insert、update、delete、query等方法来传值来拼接sql，前一种适合熟练掌握sql 语句的
3、对需要数据同步的处理请添加事务处理，熟悉事务的处理方式
4、了解各个方法参数的意义以及传值
5、掌握ListView显示后台数据的使用方法
SimpleAdapter、SimpleCursorAdapter以及自定义适配器的使用，以及OnItemClickListener取值时各个适配器返回值的区别以及取值方法
6、多学、多记、多练、多思，加油！