SQLiteDatabase里面的简单操作数据库的方法

正文

数据库初始化

package com.example.bookdemo2;

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

import androidx.annotation.Nullable;

public class DBOpenHelper2 extends SQLiteOpenHelper {
    public DBOpenHelper2(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {

        String sql="create table book(id integer primary key autoincrement,bookname varchar(20),bookauthor varchar(20),booktextnumber integer)";
        db.execSQL(sql);


    }

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

    }
}

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其中oncreate中的sql语句用于创建表，以及表的字段

增

DBOpenHelper2 dbsqLiteOpenHelper = new DBOpenHelper2(MainActivity.this, "books.db", null, 1);
        db = dbsqLiteOpenHelper.getWritableDatabase();
        //创建存放数据的ContentValues对象
        ContentValues values = new ContentValues();
        values.put("bookname", "刁民王小二");
        values.put("bookauthor", "拾伍");
        values.put("booktextnumber", "1991000" + "个字");
        Log.e("moli", "添加书籍1成功");
        //数据库执行插入命令
        db.insert("book", null, values);
        values.put("bookname", "万夜之主");
        values.put("bookauthor", "一柄墨刀");
        values.put("booktextnumber", "3764000" + "个字");
        //数据库执行插入命令
        db.insert("book", null, values);

        Log.e("moli", "添加书籍2成功");
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删

 db.delete("book", null, null);
                bookList.clear();
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一个是删数据库，一个是删list列表

改

ContentValues values = new ContentValues();
 values.put("price", 10.99); 
 db.update("Book", values, "name = ?", new String[] { "The Da Vinci Code" }); }
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查

 //创建游标对象
                Cursor cursor = db.query("book", new String[]{"id","bookname","bookauthor","booktextnumber"}, null, null, null, null, null);
                //利用游标遍历所有数据对象
                while(cursor.moveToNext()){
                    @SuppressLint("Range") String id = cursor.getString(cursor.getColumnIndex("id"));
                    @SuppressLint("Range") String bookname = cursor.getString(cursor.getColumnIndex("bookname"));
                    @SuppressLint("Range") String bookauthor=cursor.getString(cursor.getColumnIndex("bookauthor"));
                    @SuppressLint("Range") String booktextnumber = cursor.getString(cursor.getColumnIndex("booktextnumber"));
                    Log.i("moli","result: id="  + id +" bookname: " + bookname +" bookauthor: "+bookauthor+" booktextnumber: "+ booktextnumber);
              Book book=new Book(bookauthor,bookname,booktextnumber,"1");
                    bookList.add(book);
                }
                // 关闭游标，释放资源
                cursor.close();
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最后记得设置适配器来更新UI界面

 recyclerViewAdapter = new RecyclerViewAdapter(bookList);
                    recyclerViewAdapter.notifyItemInserted(0);
                    recyclerView.setAdapter(recyclerViewAdapter);
                    recyclerViewAdapter.notifyDataSetChanged();
           
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SQLiteOpenHelper

SQLiteOpenHelper是个抽象类，没有实现类，所以要创建实现类来继承SQLiteOpenHelper，来重写方法

按ctrl+鼠标左键点击SQLiteOpenHelper，可查看源代码。看官方注释就能看到各参数的作用

游标cursor 作用类似于可以游动的指针，用于定位数据库的元素

Context为内容，哪个activity要使用数据库就用哪个context

这两行代码用于创建数据库文件

DatabaseHelper helper=new DatabaseHelper(this);//创建DatabaseHelper的对象
helper.getWritableDatabase();//创建数据库
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ctrl+alt+f 使变量成为全局变量

代码如下

DBOpenHelper2.java

package com.example.bookdemo2;

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

import androidx.annotation.Nullable;

public class DBOpenHelper2 extends SQLiteOpenHelper {
    public DBOpenHelper2(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {

        String sql="create table book(id integer primary key autoincrement,bookname varchar(20),bookauthor varchar(20),booktextnumber integer)";
        db.execSQL(sql);


    }

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

    }
}
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参考来源

SQLiteDatabase里面的简单操作数据库的方法
第一行代码第二版

代码

github