Android之SQLiteOpenHelper

来源：互联网发布：2017大数据产业峰会编辑：程序博客网时间：2024/06/08 19:28

本文主要是记录一些零碎的知识点

SQLiteOpenHelper可以帮我们创建和打开数据库，这样就可以避免重复的建表带来的数据覆盖的麻烦，而且在数据库更新时也很方便

测试界面就是两个按钮，这里就不写了，有两个onClick事件，一个写数据，一个读数据

DbHelper:就一个表，只有一个id字段，一个name字段，如果有几个表，就在onCreate里多写几个ddl语句就好

import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;import android.util.Log;public class DbHelpler extends SQLiteOpenHelper {    public JohnDbHelpler(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {        super(context,name,factory,version);    }    @Override    public void onCreate(SQLiteDatabase db) {        String ddl="create table users (id integer primary key autoincrement,uname text)";        db.execSQL(ddl);    }    @Override    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {        String ddl="create table users (id integer primary key autoincrement,uname text)";        Log.i("john","upgrade.....");    }}

看看MainActivity里的实现

import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import android.net.Uri;import android.os.Environment;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import android.view.View;import java.io.File;public class MainActivity extends AppCompatActivity {    private SQLiteDatabase db;    private JohnDbHelpler dbHelpler;    private int i=0;    private File sdcardDir;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        sdcardDir= Environment.getExternalStorageDirectory();        dbHelpler=new DbHelpler(this,sdcardDir.getAbsolutePath()+"/john1.db",null,2);        db=dbHelpler.getWritableDatabase();        Log.i("<span style="font-family: Arial;">MainActivity </span><span style="font-family: Arial;">", sdcardDir.getAbsolutePath() + "...............................");</span>    }    @Override    protected void onDestroy() {        super.onDestroy();        db.close();    }    public void writeDB(View view) {        String sql="insert into users (uname) values (?)";        try {            db.beginTransaction();            db.execSQL(sql, new Object[]{"Tom" + i++});            db.setTransactionSuccessful();        }        catch (RuntimeException e){        }        finally {            db.endTransaction();        }    }    public void readDB(View view) {        String sql="select uname,id from users where id>?";        Cursor c=db.rawQuery(sql,new String[]{"2"});        while (c.moveToNext()){            String uname=c.getString(0);            int id=c.getInt(c.getColumnIndex("id"));            Log.i("MainActivity","uanme:"+uname+"........"+id);        }    }

Dbhelper里的onUpgrade只会在DbHelpler创建时，最后一个参数版本号变化时才会执行

其他的增删改查都是db可以操作的，跟普通数据库一样

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