Android編程之數(shù)據(jù)庫的創(chuàng)建方法詳解

package com.itheima.createdatabase;
import android.app.Activity;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
public class MainActivity extends Activity {
  private Context mContext;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mContext = this;
    //創(chuàng)建一個幫助類對象
    MySqliteOpenHelper mySqliteOpenHelper = new MySqliteOpenHelper(mContext);
    //調(diào)用getReadableDatabase方法,來初始化數(shù)據(jù)庫的創(chuàng)建
    SQLiteDatabase db = mySqliteOpenHelper.getReadableDatabase();
  }
}

package com.itheima.createdatabase;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
public class MySqliteOpenHelper extends SQLiteOpenHelper {
  public MySqliteOpenHelper(Context context) {
    //context :上下文  ， name：數(shù)據(jù)庫文件的名稱  factory：用來創(chuàng)建cursor對象，默認為null
    //version:數(shù)據(jù)庫的版本號，從1開始，如果發(fā)生改變，onUpgrade方法將會調(diào)用,4.0之后只能升不能將
    super(context, "info.db", null,1);
  }
  //oncreate方法是數(shù)據(jù)庫第一次創(chuàng)建的時候會被調(diào)用; 特別適合做表結(jié)構(gòu)的初始化,需要執(zhí)行sql語句；SQLiteDatabase db可以用來執(zhí)行sql語句
  @Override
  public void onCreate(SQLiteDatabase db) {
    //通過SQLiteDatabase執(zhí)行一個創(chuàng)建表的sql語句
    db.execSQL("create table info (_id integer primary key autoincrement,name varchar(20))");
  }
  //onUpgrade數(shù)據(jù)庫版本號發(fā)生改變時才會執(zhí)行； 特別適合做表結(jié)構(gòu)的修改
  @Override
  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    //添加一個phone字段
    db.execSQL("alter table info add phone varchar(11)");
  }
}

super(context, "info.db", null,1);