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安卓开发:数据库操作(详细)

程序员文章站 2022-06-23 20:42:03
安卓使用的数据库是sqlite 创建方式:新建一个类继承SQLiteOpenHelper 这里第二个参数:数据库的名字,第三个参数为结果集(游标)写成null即可,最后一个参数为数据库的版本,写1即可 在MainActivity中新建实例即可创建数据库: 好的,运行即可创建数据库成功 接下来看下My ......

安卓使用的数据库是sqlite

创建方式:新建一个类继承SQLiteOpenHelper

package org.dreamtech.sqlite;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class MyOpenHelper extends SQLiteOpenHelper {

    public MyOpenHelper(Context context) {
        super(context, "dreamtech.db", null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
    }

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

}

这里第二个参数:数据库的名字,第三个参数为结果集(游标)写成null即可,最后一个参数为数据库的版本,写1即可

 

在MainActivity中新建实例即可创建数据库:

package org.dreamtech.sqlite;

import android.os.Bundle;
import android.app.Activity;
import android.database.sqlite.SQLiteDatabase;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        MyOpenHelper myOpenHelper = new MyOpenHelper(getApplicationContext());
        // 获取一个可写的数据库,如果数据库不存在,则新建数据库
        SQLiteDatabase sqLiteDatabase = myOpenHelper.getWritableDatabase();
    }

}

 

好的,运行即可创建数据库成功

 

 

接下来看下MyOpenHelper中的方法:

oncreate:数据库第一次创建时候执行的方法

适合于初始化表结构

示例:

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table info(_id integer primary key autoincrement,name varchar(20))");
    }

 

另一个方法:onupgrade方法:

当数据库版本升级的时候调用(上边设置为1版本,如果升级成2,会运行这里的方法)

示例:这里可以修改表结构

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("alter table info add tel varchar(20)");
    }

 

注意:版本只能升,不能降级

 

接下来做一个增删改查的小案例:

使用原始方法:

package org.dreamtech.sqlite;

import android.os.Bundle;
import android.view.View;
import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

public class MainActivity extends Activity {

    private MyOpenHelper myOpenHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myOpenHelper = new MyOpenHelper(getApplicationContext());
    }

    // 增
    public void click1(View v) {
        SQLiteDatabase db = myOpenHelper.getWritableDatabase();
        db.execSQL("insert into info(name,tel) values(?,?)", new Object[] {
                "zhangsan", "110" });
        db.close();
    }

    // 删
    public void click2(View v) {
        SQLiteDatabase db = myOpenHelper.getWritableDatabase();
        db.execSQL("delete from info where name=?", new Object[] { "zhangsan" });
        db.close();
    }

    // 改
    public void click3(View v) {
        SQLiteDatabase db = myOpenHelper.getWritableDatabase();
        db.execSQL("update info set tel=? where name=?", new Object[] { "120",
                "zhangsan" });
        db.close();
    }

    // 查
    public void click4(View v) {
        SQLiteDatabase db = myOpenHelper.getWritableDatabase();
        Cursor cursor = db.rawQuery("select * from info", null);
        if (cursor != null && cursor.getCount() > 0) {
            while (cursor.moveToNext()) {
                String name = cursor.getString(1);
                String tel = cursor.getString(2);
                System.out.println(name + "   " + tel);
            }
        }
        db.close();
    }
}

 

确实成功了,但是存在问题:sql语句只要一处出错,将难以发现,浪费大量时间

唯一的优点:多表查询

 

通常操作数据库是采用谷歌封装好的API:

 优点:不易写错,有返回值,方便开发

 缺点:涉及多表操作不便

package org.dreamtech.sqlite;

import android.os.Bundle;
import android.view.View;
import android.widget.Toast;
import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

public class MainActivity extends Activity {

    private MyOpenHelper myOpenHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myOpenHelper = new MyOpenHelper(getApplicationContext());
    }

    // 增
    public void click1(View v) {
        SQLiteDatabase db = myOpenHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("name", "zhangsan");
        values.put("tel", "110");
        // 返回新行的id
        long insert = db.insert("info", null, values);
        db.close();
        if (insert > 0) {
            Toast.makeText(getApplicationContext(), "add 成功", Toast.LENGTH_LONG)
                    .show();
        } else {
            Toast.makeText(getApplicationContext(), "add 失败", Toast.LENGTH_LONG)
                    .show();
        }
    }

    // 删
    public void click2(View v) {
        SQLiteDatabase db = myOpenHelper.getWritableDatabase();
        // 返回值:影响的行数
        int delete = db.delete("info", "name=?", new String[] { "zhangsan" });
        db.close();
        Toast.makeText(getApplicationContext(), "删除了" + delete + "行",
                Toast.LENGTH_LONG).show();
    }

    // 改
    public void click3(View v) {
        SQLiteDatabase db = myOpenHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("tel", "666");
        // 返回值:更新了多少行
        int update = db.update("info", values, "name=?",
                new String[] { "zhangsan" });
        db.close();
        Toast.makeText(getApplicationContext(), "更新了" + update + "行",
                Toast.LENGTH_LONG).show();
    }

    // 查
    public void click4(View v) {
        SQLiteDatabase db = myOpenHelper.getWritableDatabase();

        Cursor cursor = db.query("info", new String[] { "tel" }, "name=?",
                new String[] { "zhangsan" }, null, null, null);

        if (cursor != null && cursor.getCount() > 0) {
            while (cursor.moveToNext()) {
                String tel = cursor.getString(0);
                System.out.println(tel);
            }
        }
        db.close();
    }
}

 

 

事务操作:执行一段逻辑,要么同时成功,要么同时失败

这里写一个逻辑转账的案例

 

package org.dreamtech.transaction;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class MyOpenHelper extends SQLiteOpenHelper {

    public MyOpenHelper(Context context) {
        super(context, "Account.db", null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table info(_id integer primary key autoincrement,name varchar(20),money varchar(20))");
        db.execSQL("insert into info('name','money') values('a','2000')");
        db.execSQL("insert into info('name','money') values('b','5000')");
    }

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

}

 

package org.dreamtech.transaction;

import android.os.Bundle;
import android.app.Activity;
import android.database.sqlite.SQLiteDatabase;
import android.view.Menu;
import android.view.View;
import android.widget.Toast;

public class MainActivity extends Activity {

    private MyOpenHelper myOpenHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myOpenHelper = new MyOpenHelper(getApplicationContext());
    }

    // 使用事务进行转账
    public void click(View v) {
        SQLiteDatabase db = myOpenHelper.getReadableDatabase();

        // 开启事务
        db.beginTransaction();
        try {
            // 转账逻辑
            db.execSQL("update info set money=money-100 where name=?",
                    new Object[] { "a" });
            // 加入这一行则不会成功
            // int a = 10/0;
            db.execSQL("update info set money=money+100 where name=?",
                    new Object[] { "b" });
            // 表示当前事务成功(自动提交)
            db.setTransactionSuccessful();
        } catch (Exception e) {
            Toast.makeText(getApplicationContext(), "转账失败", Toast.LENGTH_LONG)
                    .show();
        } finally {
            // 关闭事务
            db.endTransaction();
        }

    }
}

 

加入10/0一行的效果:

安卓开发:数据库操作(详细)