Android之SQLLite

最新推荐文章于 2021-12-19 19:04:43 发布

转载最新推荐文章于 2021-12-19 19:04:43 发布 · 853 阅读

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本文介绍了一个简单的Android应用程序中使用SQLite数据库进行增删查改(CRUD)操作的示例代码。通过具体的Java代码展示了如何创建数据库帮助器类、执行插入、更新、删除及查询等基本操作。

package com.duantl.service;

import java.util.ArrayList;
import java.util.List;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

import com.duantl.domain.Person;

public class PersonService {

private DBOpenHelper dbOpenHelper;
private Context context;

public PersonService(Context context) {
this.dbOpenHelper = new DBOpenHelper(context);
}

public void save(Person person) {
  // 如果要对数据进行更改，就调用此方法得到用于操作数据库的实例,该方法一读和写方式打开数据库
  SQLiteDatabase db = dbOpenHelper.getWritableDatabase();
  // 如果只对数据库进行读取，建议使用此方法,但此方法并不是以只读方式打开数据库的。因为该方法内部调用了getWritableDatabase方法
  // SQLiteDatabase db2 = dbOpenHelper.getReadableDatabase();
  // 用占位符可防止用户输入出现问题
  db.execSQL("insert into person (name) values (?)",
    new Object[] { person.getName() });
  // 如果该数据库只被本应用访问，android不建议关闭数据库，为了性能
  // db.close();

}

public void update(Person person) {
  SQLiteDatabase db = dbOpenHelper.getWritableDatabase();
  db.execSQL("update person set name=? where personid=?", new Object[] {
    person.getName(), person.getId() });
}

public void delete(Integer id) {
  SQLiteDatabase db = dbOpenHelper.getWritableDatabase();
  db.execSQL("delete from person where personid=?", new Object[] { id
    .toString() });
}

public Person find(Integer id) {
  SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
  Cursor cursor = db.rawQuery("select * from person where personid=?", new String[]{id.toString()});
  if (cursor.moveToFirst()) {
   int personid = cursor.getInt(cursor.getColumnIndex("personid"));
   String name = cursor.getString(cursor.getColumnIndex("name"));
   return new Person(personid,name);
  }
  return null;
}

public List<Person> getScrollData(Integer offset, Integer maxResult) {
  List<Person> persons = new ArrayList<Person>();
  SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
  Cursor cursor = db.rawQuery("select * from person limit ?,?",
       new String[]{offset.toString(),maxResult.toString()});
  while(cursor.moveToNext()) {
   int personid = cursor.getInt(cursor.getColumnIndex("personid"));
   String name = cursor.getString(cursor.getColumnIndex("name"));
   Person person = new Person(personid, name);
   persons.add(person);
  }
  cursor.close();
  return persons;
}

public long getCount() {
  SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
  Cursor cursor = db.rawQuery("select count(*) from person", null);
  cursor.moveToFirst();
  return cursor.getLong(0);
}

}