存储方式三:数据库SQLite（SQLiteOpenHelper）

q6542125

SQLHelper.java

package com.example.sqlitedemo;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class SQLHelper extends SQLiteOpenHelper {
private static final String dbName="mydb.db";
private static final int version=2;
public SQLHelper(Context context) {
super(context, dbName, null, version);
}
//调用getWritableDatabase()或getReadableDatabase()时，会检查数据库是否存在，若不存在则会调用此方法
@Override
public void onCreate(SQLiteDatabase db) {
System.out.println("onCreate");
String sql="create table mytable (id integer primary key,name varchar(10) not null)";
db.execSQL(sql);
}
//当版本号更新时会调用此方法
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
System.out.println("onUpgrade");
String sql="drop table if exists mytable";
db.execSQL(sql);
onCreate(db);
}
}


Main.java

package com.example.sqlitedemo;
import android.app.Activity;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.Bundle;
public class Main extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
SQLiteOpenHelper helper=new SQLHelper(this);
helper.getWritableDatabase();
}
}