Android中SQLite应用详解

参考文章：http://blog.csdn.net/liuhe688/article/details/6715983

本文只是记录一下sqlite应用的过程。

 

 

程序结构如下：

其中，DBManger继承DBHelper, Person是一个实体类，MyActivity是一个主界面，main.xml里面定义了一个listview。

1. 编写DBHelper
   1. package com.example.myapp;
   2.  
   3. import android.content.Context;
   4. import android.database.sqlite.SQLiteDatabase;
   5. import android.database.sqlite.SQLiteOpenHelper;
   6.  
   7. /**
   8.  * Created by zhuxuekui on 2015/5/18.
   9.  */
   10. public class DBHelper extends SQLiteOpenHelper {
   11.     private static final String name = "test.db";
   12.     private static final int version = 1;
   13.     @Override
   14.     public void onCreate(SQLiteDatabase sqLiteDatabase) {
   15.         sqLiteDatabase.execSQL("create table if not exists person"
   16.         + "(_id integer primary key autoincrement , name varchar , age integer, info text )");
   17.     }
   18.  
   19.     @Override
   20.     public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
   21.         sqLiteDatabase.execSQL("alter table person add column other siring");
   22.     }
   23.  
   24.     public DBHelper(Context context) {
   25.         super(context, name, null, version);
   26.     }
   27. }

此类在数据库第一次创建时，通过构造方法执行。 然后执行onCreate,创建person表，除非我们卸载应用，不然就不会再次执行oncreate，当系统发现版本变化之后，我们会调用onUpgrade去更新，这里我们执行某些修改表的操作。

其中，我们通过version去判断是不是需要更新。

1. 接下来，我们编写Person数据表对应的实体类
   1. package com.example.myapp;
   2.  
   3. /**
   4.  * Created by zhuxuekui on 2015/5/18.
   5.  */
   6. public class Person {
   7.     public int _id;
   8.     public String name;
   9.     public int age;
   10.     public String info;
   11.  
   12.     public Person(String name, int age, String info) {
   13.         this.name = name;
   14.         this.age = age;
   15.         this.info = info;
   16.     }
   17.     public Person()
   18.     {
   19.  
   20.     }
   21.  
   22. }

   实体类，没啥好讲，加入我们声明成private，这就需要set，get一下了。封装好然后下面在调用。

2. 下面就是重头戏了，主要涉及数据库的增删改查
   1.  
   2. import java.util.ArrayList;
   3. import java.util.List;
   4.  
   5. import android.content.ContentValues;
   6. import android.content.Context;
   7. import android.database.Cursor;
   8. import android.database.sqlite.SQLiteDatabase;
   9.  
   10. public class DBManager {
   11.    private DBHelper helper;
   12.    private SQLiteDatabase db;
   13.  
   14.    public DBManager(Context context) {
   15.       helper = new DBHelper(context);
   16.       //因为getWritableDatabase内部调用了mContext.openOrCreateDatabase(mName, 0, mFactory);
   17.       //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
   18.       db = helper.getWritableDatabase();
   19.    }
   20.  
   21.    /**
   22.     * add persons
   23.     * @param persons
   24.     */
   25.    public void add(List<Person> persons) {
   26.         db.beginTransaction(); //开始事务
   27.         try {
   28.            for (Person person : persons) {
   29.               db.execSQL("INSERT INTO person VALUES(null, ?, ?, ?)", new Object[]{person.name, person.age, person.info});
   30.            }
   31.            db.setTransactionSuccessful(); //设置事务成功完成
   32.         } finally {
   33.            db.endTransaction(); //结束事务
   34.         }
   35.    }
   36.  
   37.    /**
   38.     * update person's age
   39.     * @param person
   40.     */
   41.    public void updateAge(Person person) {
   42.       ContentValues cv = new ContentValues();
   43.       cv.put("age", person.age);
   44.       db.update("person", cv, "name = ?", new String[]{person.name});
   45.    }
   46.  
   47.    /**
   48.     * delete old person
   49.     * @param person
   50.     */
   51.    public void deleteOldPerson(Person person) {
   52.       db.delete("person", "age >= ?", new String[]{String.valueOf(person.age)});
   53.    }
   54.  
   55.    /**
   56.     * query all persons, return list
   57.     * @return List<Person>
   58.     */
   59.    public List<Person> query() {
   60.       ArrayList<Person> persons = new ArrayList<Person>();
   61.       Cursor c = queryTheCursor();
   62.         while (c.moveToNext()) {
   63.            Person person = new Person();
   64.            person._id = c.getInt(c.getColumnIndex("_id"));
   65.            person.name = c.getString(c.getColumnIndex("name"));
   66.            person.age = c.getInt(c.getColumnIndex("age"));
   67.            person.info = c.getString(c.getColumnIndex("info"));
   68.            persons.add(person);
   69.         }
   70.         c.close();
   71.         return persons;
   72.    }
   73.  
   74.    /**
   75.     * query all persons, return cursor
   76.     * @return Cursor
   77.     */
   78.    public Cursor queryTheCursor() {
   79.         Cursor c = db.rawQuery("SELECT * FROM person", null);
   80.         return c;
   81.    }
   82.  
   83.    /**
   84.     * close database
   85.     */
   86.    public void closeDB() {
   87.       db.close();
   88.    }
   89. }

   在DBManager中实例化dbHelper,然后通过dbHelper得到一个SQLiteDatabase对象，作为整个应用的数据库实例；在add方法中，我们应用了事务去处理，先beginTransaction，然后设置事务成功，结束事务。这里就不需要提交了commit了。这是另一种事务的写法。当然，在执行增删改的过程中，我们可以通过exec (sql语句)来完成，也可以通过db.update() db.insert() 等方法完成。或者需要声明ContentValues 对象。

3. 编写xml文件，用于主界面的布局

   

   界面部分没啥可讲，基本功。

4. 编写主要业务逻辑部分
   1. package com.scott.db;
   2.  
   3. import java.util.ArrayList;
   4. import java.util.HashMap;
   5. import java.util.List;
   6. import java.util.Map;
   7.  
   8. import android.app.Activity;
   9. import android.database.Cursor;
   10. import android.database.CursorWrapper;
   11. import android.os.Bundle;
   12. import android.view.View;
   13. import android.widget.ListView;
   14. import android.widget.SimpleAdapter;
   15. import android.widget.SimpleCursorAdapter;
   16.  
   17.  
   18. public class MainActivity extends Activity {
   19.  
   20.    private DBManager mgr;
   21.    private ListView listView;
   22.  
   23.     @Override
   24.     public void onCreate(Bundle savedInstanceState) {
   25.         super.onCreate(savedInstanceState);
   26.         setContentView(R.layout.main);
   27.         listView = (ListView) findViewById(R.id.listView);
   28.         //初始化DBManager
   29.         mgr = new DBManager(this);
   30.     }
   31.  
   32.     @Override
   33.     protected void onDestroy() {
   34.        super.onDestroy();
   35.        //应用的最后一个Activity关闭时应释放DB
   36.        mgr.closeDB();
   37.     }
   38.  
   39.     public void add(View view) {
   40.        ArrayList<Person> persons = new ArrayList<Person>();
   41.  
   42.        Person person1 = new Person("Ella", 22, "lively girl");
   43.        Person person2 = new Person("Jenny", 22, "beautiful girl");
   44.        Person person3 = new Person("Jessica", 23, "sexy girl");
   45.        Person person4 = new Person("Kelly", 23, "hot baby");
   46.        Person person5 = new Person("Jane", 25, "a pretty woman");
   47.  
   48.        persons.add(person1);
   49.        persons.add(person2);
   50.        persons.add(person3);
   51.        persons.add(person4);
   52.        persons.add(person5);
   53.  
   54.        mgr.add(persons);
   55.     }
   56.  
   57.     public void update(View view) {
   58.        Person person = new Person();
   59.        person.name = "Jane";
   60.        person.age = 30;
   61.        mgr.updateAge(person);
   62.     }
   63.  
   64.     public void delete(View view) {
   65.        Person person = new Person();
   66.        person.age = 30;
   67.        mgr.deleteOldPerson(person);
   68.     }
   69.  
   70.     public void query(View view) {
   71.        List<Person> persons = mgr.query();
   72.        ArrayList<Map<String, String>> list = new ArrayList<Map<String, String>>();
   73.        for (Person person : persons) {
   74.           HashMap<String, String> map = new HashMap<String, String>();
   75.           map.put("name", person.name);
   76.           map.put("info", person.age + " years old, " + person.info);
   77.           list.add(map);
   78.        }
   79.        SimpleAdapter adapter = new SimpleAdapter(this, list, android.R.layout.simple_list_item_2,
   80.                 new String[]{"name", "info"}, new int[]{android.R.id.text1, android.R.id.text2});
   81.        listView.setAdapter(adapter);
   82.     }
   83.  
   84.     public void queryTheCursor(View view) {
   85.        Cursor c = mgr.queryTheCursor();
   86.        startManagingCursor(c); //托付给activity根据自己的生命周期去管理Cursor的生命周期
   87.        CursorWrapper cursorWrapper = new CursorWrapper(c) {
   88.           @Override
   89.           public String getString(int columnIndex) {
   90.              //将简介前加上年龄
   91.              if (getColumnName(columnIndex).equals("info")) {
   92.                 int age = getInt(getColumnIndex("age"));
   93.                 return age + " years old, " + super.getString(columnIndex);
   94.              }
   95.              return super.getString(columnIndex);
   96.           }
   97.        };
   98.        //确保查询结果中有"_id"列
   99.       SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, android.R.layout.simple_list_item_2,
   100.             cursorWrapper, new String[]{"name", "info"}, new int[]{android.R.id.text1, android.R.id.text2});
   101.       ListView listView = (ListView) findViewById(R.id.listView);
   102.       listView.setAdapter(adapter);
   103.     }
   104. }

   这里面的代码和DBManger里面的代码结构上很相似，这里面在query处，我们用到了simpleAdapter.。这种主要接受list对象，Hashmap也可以。然后，做一些适配。结果如下：