android增删功能代码,Android SQLite增删查改实例代码部分

最新推荐文章于 2021-07-11 12:07:18 发布

珠仪

最新推荐文章于 2021-07-11 12:07:18 发布

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文章标签： android增删功能代码

本文通过一个实例详细讲解了如何在Android应用中封装SQLite数据库操作，包括创建DBHelper类继承SQLiteOpenHelper，实现数据库版本管理和表创建，定义User类映射数据表，以及创建DBManager类封装增删查改业务逻辑，最后展示了在Activity中的应用和交互。

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在 Android与SQLite数据库这个专题里我们谈到了 SQLite 的基本应用，但在实际开发中，为了能够更好的管理和维护数据库，我们会封装一个继承自 SQLiteOpenHelper 类的数据库操作类，然后以这个类为基础，再封装我们的业务逻辑方法。下面，我们就以一个实例来讲解具体的用法。

程序比较简单，由以下五个文件组成：

TestDBActivity.java

listView_db.xml

User.java

DBHelper.java

DBManager.java

1. 首先编写 DBHelper，它继承了 SQLiteOpenHelper，作为维护和管理数据库的基类。

数据库第一次创建时onCreate方法会被调用，我们可以执行创建表的语句，当系统发现版本变化之后，会调用onUpgrade方法，我们可以执行修改表结构等语句。

package net.nowamagic.test;

import android.content.Context;

import android.database.sqlite.SQLiteDatabase;

import android.database.sqlite.SQLiteOpenHelper;

public class DBHelper extends SQLiteOpenHelper {

private static final String DATABASE_NAME = "nowamagic.db";

private static final int DATABASE_VERSION = 1;

public DBHelper(Context context) {

//CursorFactory设置为null,使用默认值

super(context, DATABASE_NAME, null, DATABASE_VERSION);

}

//数据库第一次被创建时onCreate会被调用

@Override

public void onCreate(SQLiteDatabase db) {

db.execSQL("CREATE TABLE IF NOT EXISTS user" +

"(_id INTEGER PRIMARY KEY AUTOINCREMENT, name VARCHAR, age INTEGER, info TEXT)");

}

//如果DATABASE_VERSION值被改为2,系统发现现有数据库版本不同,即会调用onUpgrade

@Override

public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

db.execSQL("ALTER TABLE user ADD COLUMN other STRING");

}

2. 为了方便我们面向对象的使用数据，我们建一个 User 类，对应 user 表中的字段，如下：

package net.nowamagic.test;

public class User {

public int _id;

public String name;

public int age;

public String info;

public User() {

}

public User(String name, int age, String info) {

this.name = name;

this.age = age;

this.info = info;

}

3. 然后，我们需要一个DBManager，来封装我们所有的业务方法，代码如下：

我们在DBManager构造方法中实例化DBHelper并获取一个SQLiteDatabase对象，作为整个应用的数据库实例；在添加多个Person信息时，我们采用了事务处理，确保数据完整性；最后我们提供了一个closeDB方法，释放数据库资源，这一个步骤在我们整个应用关闭时执行，这个环节容易被忘记，所以朋友们要注意。

package net.nowamagic.test;

import java.util.ArrayList;

import java.util.List;

import android.content.ContentValues;

import android.content.Context;

import android.database.Cursor;

import android.database.sqlite.SQLiteDatabase;

import android.util.Log;

import android.widget.Toast;

public class DBManager {

private DBHelper helper;

private SQLiteDatabase db;

Context c;

public DBManager(Context context) {

helper = new DBHelper(context);

//因为getWritableDatabase内部调用了mContext.openOrCreateDatabase(mName, 0, mFactory);

//所以要确保context已初始化,我们可以把实例化DBManager的步骤放在Activity的onCreate里

db = helper.getWritableDatabase();

c = context;

}

/**

* add users

* @param users

public void add(List users) {

db.beginTransaction(); //开始事务

try {

for (User user : users) {

db.execSQL("INSERT INTO user VALUES(null, ?, ?, ?)", new Object[]{user.name, user.age, user.info});

}

db.setTransactionSuccessful(); //设置事务成功完成

} finally {

db.endTransaction(); //结束事务

}

/**

* update user's age

* @param user

public void insertUser(User user) {

ContentValues cv = new ContentValues();

cv.put("age", user.age);

cv.put("name", user.name);

cv.put("info", user.info);

long rowid = db.insert("user", null, cv);

Toast.makeText(c, "已插入一条测试数据，id =" + rowid, Toast.LENGTH_SHORT).show();

}

/**

* update user's age

* @param user

public void updateAge(User user) {

ContentValues cv = new ContentValues();

cv.put("age", user.age);

db.update("user", cv, "name = ?", new String[]{user.name});

}

/**

* delete old user

* @param user

public void deleteOldUser(User user) {

//db.delete("user", "age >= ?", new String[]{String.valueOf(user.age)});

int lastid = getTableRow();

user._id = lastid;

//String s = lastid;

//return lastid;

if(user._id > 0)

Toast.makeText(c, "已删除第 "+ lastid +" 行(最末行)数据", Toast.LENGTH_SHORT).show();

db.delete("user", "_id = ?", new String[]{String.valueOf(user._id)});

Log.i("nowamagicdb", "last_id=>" + lastid);

if(user._id == 0)

Toast.makeText(c, "数据库已清空", Toast.LENGTH_SHORT).show();

//db.delete("user", "_id = ?", new String[]{String.valueOf(user._id)});

}

/**

* query all users, return list

* @return List

public List query() {

ArrayList users = new ArrayList();

Cursor c = queryTheCursor();

while (c.moveToNext()) {

User user = new User();

user._id = c.getInt(c.getColumnIndex("_id"));

user.name = c.getString(c.getColumnIndex("name"));

user.age = c.getInt(c.getColumnIndex("age"));

user.info = c.getString(c.getColumnIndex("info"));

users.add(user);

}

c.close();

return users;

}

/**

* query all users, return cursor

* @return Cursor

public Cursor queryTheCursor() {

Cursor c = db.rawQuery("SELECT * FROM user", null);

return c;

}

/**

* close database

public void closeDB() {

db.close();

}

public int getTableRow(){

Cursor c = queryTheCursor();

if (c.moveToLast() == false)

{

//为空的Cursor

return 0;

}

else

{

int user_id = c.getInt(c.getColumnIndex("_id"));

return user_id;

}

//c.moveToLast();

}

4. 最后就是 TestDBActivity 了：

package net.nowamagic.magicapp_v17;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

import android.app.Activity;

import android.content.ContentValues;

import android.database.Cursor;

import android.database.CursorWrapper;

import android.os.Bundle;

import android.support.v4.widget.SimpleCursorAdapter;

import android.view.View;

import android.widget.ListView;

import android.widget.SimpleAdapter;

import android.widget.Toast;

import net.nowamagic.test.DBManager;

import net.nowamagic.test.User;

public class TestDBActivity extends Activity {

private DBManager mgr;

private ListView listView;

@Override

protected void onCreate(Bundle savedInstanceState) {

// TODO Auto-generated method stub

super.onCreate(savedInstanceState);

setContentView(R.layout.testdb2);

listView = (ListView) findViewById(R.id.listView_db);

//初始化DBManager

mgr = new DBManager(this);

//Toast.makeText(getApplicationContext(), "欢迎来到简明现代魔法～", Toast.LENGTH_SHORT).show();

}

@Override

protected void onDestroy() {

super.onDestroy();

//应用的最后一个Activity关闭时应释放DB

mgr.closeDB();

}

public void add(View view) {

ArrayList users = new ArrayList();

User user1 = new User("Vorn", 17, "堤格尔维尔穆德·冯伦");

User user2 = new User("Eleonora Viltaria", 17, "艾蕾欧诺拉·维尔塔利亚");

User user3 = new User("Ludmilla Lurie", 16, "琉德米拉·露利叶");

User user4 = new User("Sophia Obertas", 20, "苏菲亚·欧贝达斯");

User user5 = new User("Alexandra Alshavin", 22, "亚莉莎德拉·阿尔夏芬");

users.add(user1);

users.add(user2);

users.add(user3);

users.add(user4);

users.add(user5);

mgr.add(users);

Toast.makeText(this, "已添加测试数据", Toast.LENGTH_SHORT).show();

query(view);

}

public void insert(View view) {

User user = new User();

user.name = "Gonn";

user.age = 99;

user.info = "简明现代魔法";

mgr.insertUser(user);

query(view);

}

public void update(View view) {

User user = new User();

user.name = "Vorn";

user.age = 20;

mgr.updateAge(user);

}

public void delete(View view) {

User user = new User();

user.age = 30;

mgr.deleteOldUser(user);

query(view);

//Toast.makeText(this, "", Toast.LENGTH_SHORT).show();

}

public void query(View view) {

List users = mgr.query();

ArrayList> list = new ArrayList>();

for (User user : users) {

HashMap map = new HashMap();

map.put("name", user.name);

map.put("info", user.age + " years old, " + user.info);

list.add(map);

}

SimpleAdapter adapter = new SimpleAdapter(this, list, android.R.layout.simple_list_item_2,

new String[]{"name", "info"}, new int[]{android.R.id.text1, android.R.id.text2});

listView.setAdapter(adapter);

}

public void queryTheCursor(View view) {

Cursor c = mgr.queryTheCursor();

startManagingCursor(c); //托付给activity根据自己的生命周期去管理Cursor的生命周期

CursorWrapper cursorWrapper = new CursorWrapper(c) {

@Override

public String getString(int columnIndex) {

//将简介前加上年龄

if (getColumnName(columnIndex).equals("info")) {

int age = getInt(getColumnIndex("age"));

return age + " years old, " + super.getString(columnIndex);

}

return super.getString(columnIndex);

}

};

//确保查询结果中有"_id"列

SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, android.R.layout.simple_list_item_2,

cursorWrapper, new String[]{"name", "info"}, new int[]{android.R.id.text1, android.R.id.text2});

ListView listView = (ListView) findViewById(R.id.listView_db);

listView.setAdapter(adapter);

}

其XML如下：

android:orientation="horizontal"