Android开发之Sqlite的使用
在Android中存储数据可以用文件、数据库、网络，其中文件和数据库是最常用的，数据库我们常用的就是Sqlite，它是一种经量级的、嵌入式的关系型数据库；在android中当需要操作SQLite数据库的时候需要得到一个SQLiteOpenHelper对象，而SQLiteOpenHelper是一个抽象类，用户需要继承这个类
package com.example.sqlite.db;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
/**
* DatabaseHelper作为一个访问SQLite的助手类，提供两个方面的功能，
* 第一，getReadableDatabase(),getWritableDatabase()可以获得SQLiteDatabse对象，通过该对象可以对数据库进行操作
* 第二，提供了onCreate()和onUpgrade()两个回调函数，允许我们在创建和升级数据库时，进行自己的操作
* @author Administrator
*
*/
public class DatabaseHelper extends SQLiteOpenHelper{
public static final int VERSION = 1;
public DatabaseHelper(Context context, String name, CursorFactory factory,
int version) {
super(context, name, factory, version);
// TODO Auto-generated constructor stub
}
public DatabaseHelper(Context context, String name){
this(context, name, VERSION);
Log.i("debug", "DatabaseHelper");
}
public DatabaseHelper(Context context, String name, int version){
this(context, name, null, version);
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
Log.i("debug", "create a database");
//执行SQL语句
db.execSQL("create table user (id int, name varchar(20))");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
Log.i("debug", "Upgrade a database");
}
}
下面是对数据库的进行增、删、改、查操作
布局文件
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<Button
android:id="@+id/create_db"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/create_db"/>
<Button
android:id="@+id/update_db"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/update_db"/>
<Button
android:id="@+id/insert"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/insert"/>
<Button
android:id="@+id/update"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/update"/>
<Button
android:id="@+id/query"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/query"/>
<Button
android:id="@+id/delete"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/delete"/>
</LinearLayout>
在Activity处理代码
package com.example.sqlite;
import com.example.sqlite.db.DatabaseHelper;
import android.os.Bundle;
import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
/**
* SQLite的创建、更新、修改、插入、查询、删除操作
* @author Administrator
*
*/
public class SqliteActivity extends Activity {
private Button create_db;
private Button update_db; //更新数据库的版本号
private Button insert;
private Button update;
private Button query;
private Button delete;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sqlite);
create_db = (Button)findViewById(R.id.create_db);
update_db = (Button)findViewById(R.id.update_db);
insert = (Button)findViewById(R.id.insert);
update = (Button)findViewById(R.id.update);
query = (Button)findViewById(R.id.query);
delete = (Button)findViewById(R.id.delete);
create_db.setOnClickListener(new CreateListener());
update_db.setOnClickListener(new UpdateDBListener());
insert.setOnClickListener(new InsertListener());
update.setOnClickListener(new UpdateListener());
query.setOnClickListener(new QueryListener());
delete.setOnClickListener(new Deletelistener());
}
class CreateListener implements OnClickListener{
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
Log.i("debug", "on create db");
DatabaseHelper dbHelper = new DatabaseHelper(SqliteActivity.this, "text_mars_db");
//只有调用了DatabaseHelper的getReadableDatabase()或getWritableDatabase()才会创建数据库
SQLiteDatabase db = dbHelper.getWritableDatabase();
}
}
/**
* 更新数据库的版本号
* @author Administrator
*
*/
class UpdateDBListener implements OnClickListener{
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
Log.i("debug", "on update db");
DatabaseHelper dbHelper = new DatabaseHelper(SqliteActivity.this, "text_mars_db", 2);
SQLiteDatabase db = dbHelper.getReadableDatabase();
}
}
class InsertListener implements OnClickListener{
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Log.i("debug", "insert db");
ContentValues values = new ContentValues();
//向该对象插入键值对，其中键是列名，值是希望插入这一列的值，值的数据类型必须一致
values.put("id", 1);
values.put("name", "zhang");
DatabaseHelper dbHelper = new DatabaseHelper(SqliteActivity.this, "text_mars_db");
SQLiteDatabase db = dbHelper.getWritableDatabase();
//调用insert方法插入数据
db.insert("user", null, values);
}
}
class UpdateListener implements OnClickListener{
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Log.i("debug", "update db");
DatabaseHelper dbHelper = new DatabaseHelper(SqliteActivity.this, "text_mars_db");
SQLiteDatabase db = dbHelper.getWritableDatabase();
ContentValues values = new ContentValues();
values.put("name", "zhangsanfeng");
//第一个参数是要更新的表名
//第二个参数是一个ContentValeus对象
//第三个参数是where子句
db.update("user", values, "id=?", new String[]{"1"});
}
}
class QueryListener implements OnClickListener{
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Log.i("debug", "query db");
DatabaseHelper dbHelper = new DatabaseHelper(SqliteActivity.this, "text_mars_db");
SQLiteDatabase db = dbHelper.getReadableDatabase();
Cursor cursor = db.query("user", new String[]{"id","name"}, "id=?", new String[]{"1"}, null, null, null);
int count = cursor.getCount();
System.out.println("query---count = >" + count);
while(cursor.moveToNext()){
String name = cursor.getString(cursor.getColumnIndex("name"));
System.out.println("query--->" + name);
}
}
}
class Deletelistener implements OnClickListener{
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Log.i("debug", "delete db");
DatabaseHelper dbHelper = new DatabaseHelper(SqliteActivity.this, "text_mars_db");
SQLiteDatabase db = dbHelper.getWritableDatabase();
db.delete("user", "id=?", new String[]{"1"});
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_sqlite, menu);
return true;
}
}
运行效果
样例代码