Android中Sqlite使用初步

1、使用Sqlite的关键是创建一类，这个类继承SQLiteOpenHelper，继承的类必须重写三个方法：构造方法，onCreate方法，onUpgrate方法

2、SQLiteDatabase是直接操作数据库的对象，可以使用SQLiteOpenHelper的getReadableDatabase或getWritableDatabase方法得到SQLiteDatabase对象。具体使用这两个方法得到的SQLiteDatabase对象的不用点，根据方法名就可以看出。一个是得到可读的，一个是得到可写的。

实例代码：

1、布局文件

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:orientation="vertical" android:layout_width="fill_parent"

android:layout_height="fill_parent">

<Button android:id="@+id/createDatabase" android:layout_width="fill_parent"

android:layout_height="wrap_content" android:text="Create Database"></Button>

<Button android:id="@+id/upgrateDatabase" android:layout_width="fill_parent"

android:layout_height="wrap_content" android:text="Upgrate Database"></Button>

<Button android:id="@+id/insert" android:layout_width="fill_parent"

android:layout_height="wrap_content" android:text="Insert"></Button>

<Button android:id="@+id/update" android:layout_width="fill_parent"

android:layout_height="wrap_content" android:text="Update"></Button>

<Button android:id="@+id/query" android:layout_width="fill_parent"

android:layout_height="wrap_content" android:text="Query"></Button>

<Button android:id="@+id/delete" android:layout_width="fill_parent"

android:layout_height="wrap_content" android:text="Delete"></Button>

</LinearLayout>

2、自定义继承SQLiteOpenHelper的类，重写三个方法

package yyl.db;

import android.content.Context;

import android.database.sqlite.SQLiteDatabase;

import android.database.sqlite.SQLiteDatabase.CursorFactory;

import android.database.sqlite.SQLiteOpenHelper;

public class DatabaseHelper extends SQLiteOpenHelper {

//构造函数

public DatabaseHelper(Context context,String name,CursorFactory factory, int version)

{

super(context,name,factory,version);

}

//该函数在第一次创建数据库的时候执行

@Override

public void onCreate(SQLiteDatabase db) {

System.out.println("Creaet a database test_user and table user");

db.execSQL("create table user (id int,name varchar(20))");

}

@Override

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

System.out.println("upgrate a database");

}

}

3、数据库操作代码

package yyl.sqlite;

import yyl.db.DatabaseHelper;

import android.app.Activity;

import android.content.ContentValues;

import android.database.Cursor;

import android.database.sqlite.SQLiteDatabase;

import android.os.Bundle;

import android.view.View;

import android.widget.Button;

public class SqliteActivity extends Activity {

// 定义变量

private Button createDatabase = null;

private Button upgrateDatabase = null;

private Button insert = null;

private Button update = null;

private Button query = null;

private Button delete = null;

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

// 根据ID得到控件对象

createDatabase = (Button) findViewById(R.id.createDatabase);

upgrateDatabase = (Button) findViewById(R.id.upgrateDatabase);

insert = (Button) findViewById(R.id.insert);

update = (Button) findViewById(R.id.update);

query = (Button) findViewById(R.id.query);

delete = (Button) findViewById(R.id.delete);

// 给按钮绑定单击事件监听器

createDatabase.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

//生成DatabaseHelper对象

DatabaseHelper databaseHelper = new DatabaseHelper(SqliteActivity.this,"sqlite_user",null,1);

//只有调用了getReadableDatabase方法，或者getWritableDatabase方法，才会创建数据库

databaseHelper.getReadableDatabase();

}

});

upgrateDatabase.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

//生成DatabaseHelper对象

DatabaseHelper databaseHelper = new DatabaseHelper(SqliteActivity.this,"sqlite_user",null,2);

//只有调用了getReadableDatabase方法，或者getWritableDatabase方法，才会更新数据库

databaseHelper.getReadableDatabase();

}

});

insert.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

//创建ContentValue对象

ContentValues values = new ContentValues();

//插入键值对，注意值的类型必须和数据库表中字段的类型一致

values.put("id", 1);

values.put("name", "yangyulin");

//生成SQLiteDatabase对象

DatabaseHelper dbHelper = new DatabaseHelper(SqliteActivity.this,"test_user",null,1);

SQLiteDatabase db = dbHelper.getWritableDatabase();

//执行插入

db.insert("user", null, values);

}

});

update.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

//生成DatabaseHelper对象

DatabaseHelper dbHelper = new DatabaseHelper(SqliteActivity.this,"test_user",null,1);

//调用DatabaseHelper的getWritableDatabase方法，生成SQLiteDatabase对象

SQLiteDatabase db = dbHelper.getWritableDatabase();

//生成ContentValues对象，并设定键值对

ContentValues values = new ContentValues();

values.put("name", "newSky");

//更新表信息:update user set name = 'newSky' where id =1;

db.update("user", values, " id=?", new String[]{"1"});

}

});

query.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

//生成DatabaseHelper对象

DatabaseHelper dbHelper = new DatabaseHelper(SqliteActivity.this,"test_user",null,1);

//调用DatabaseHelper的getReadableDatabase方法，生成SQLiteDatabase对象

SQLiteDatabase db = dbHelper.getReadableDatabase();

//执行查询，将查询结果放入到Cursor中

Cursor cursor = db.query("user", new String[]{"id","name"}, " id =?", new String[]{"1"}, null, null, null);

//打印查询结果

while(cursor.moveToNext())

{

String name = cursor.getString(cursor.getColumnIndex("name"));

System.out.println("name --> " + name);

}

}

});

delete.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

//生成DatabaseHelper对象

DatabaseHelper dbHelper = new DatabaseHelper(SqliteActivity.this,"test_user",null,1);

//调用DatabaseHelper的getReadableDatabase方法，生成SQLiteDatabase对象

SQLiteDatabase db = dbHelper.getWritableDatabase();

db.delete("user", "id =?", new String[]{"1"});

}

});

}

}

查看数据库：

1、在CMD命令行下输入以下命令

>adb shelll

#>cd data/data/yyl.sqlite

#>cd databases

#>sqlite3 test_user

#>.schema

#>select * from user;