Android开发使用SQLite数据库

1、总体思路

1、自定义一个类​​MySqliteOpenHelper​​​继承​​SQLiteOpenHelper​​​类。
2、实现自定义类的单例模式。
3、在​​​onCreate​​​抽象方法中创建表。
4、通过单例模式获取对象实现增、删、改、查。

2、实现代码

a、自定义类实现单例模式

package com.example.learning01;

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

import androidx.annotation.Nullable;

/**
 *
 * 单例模式
 *
 */
public class MySqliteOpenHelper extends SQLiteOpenHelper {

    private  static SQLiteOpenHelper mInstance;
    public static synchronized SQLiteOpenHelper getmInstance(Context context) {
        if(mInstance == null) {
            mInstance = new MySqliteOpenHelper(context,"xupeng.dp",null,1);

        }
        return mInstance;
    }
    //将构造方法私有化
    private MySqliteOpenHelper(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        //创建表 表数据初始化
        //id的标准写法：_id
        //主键必须为1
        String sql = "create table persons(_id integer primary key autoincrement, name text)";
        sqLiteDatabase.execSQL(sql);
    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

    }
}

b、增

public void insert_db(View view) {
    SQLiteOpenHelper helper = MySqliteOpenHelper.getmInstance(this);
    SQLiteDatabase db = helper.getWritableDatabase();

    if(db.isOpen()){
        String sql = "insert into persons(name) values('xdupeng01')";

        db.execSQL(sql);
    }
    db.close();//关闭数据库
}

c、删

public void delete_db(View view) {
     SQLiteOpenHelper helper = MySqliteOpenHelper.getmInstance(this);
     SQLiteDatabase db = helper.getWritableDatabase();

     if(db.isOpen()){
         String sql = "delete from persons where _id=?";

         db.execSQL(sql,new Object[]{4});
     }
     db.close();//关闭数据库
 }

d、改

public void update_db(View view) {
    SQLiteOpenHelper helper = MySqliteOpenHelper.getmInstance(this);
    SQLiteDatabase db = helper.getWritableDatabase();

    if(db.isOpen()){
        String sql = "update persons set name=? where _id=?";

        db.execSQL(sql,new Object[]{"李连杰",5});
    }
    db.close();//关闭数据库
}

e、查

public void find_db(View view) {
    SQLiteOpenHelper helper = MySqliteOpenHelper.getmInstance(this);
    SQLiteDatabase db = helper.getReadableDatabase();
    if(db.isOpen()) {
        //返回游标
        Cursor cursor = db.rawQuery("select * from persons", null);

        while (cursor.moveToNext()) {
            @SuppressLint("Range") int _id = cursor.getInt(cursor.getColumnIndex("_id"));
            @SuppressLint("Range") String name = cursor.getString(cursor.getColumnIndex("name"));

            Log.d(TAG, "id: "+_id + "  name :"+name);
        }
        cursor.close();//关闭游标
        db.close();//关闭数据库
    }
}

3、测试代码

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">
    <Button
        android:text="生成数据库"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="create_db"/>
    <Button
        android:text="查询"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="find_db"/>
    <Button
        android:text="插入"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="insert_db"/>
    <Button
        android:text="修改"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="update_db"/>
    <Button
        android:text="删除"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="delete_db"/>
</LinearLayout>

MySqliteOpenHelper.java

package com.example.learning01;

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

import androidx.annotation.Nullable;

/**
 *
 * 单例模式
 *
 */
public class MySqliteOpenHelper extends SQLiteOpenHelper {

    private  static SQLiteOpenHelper mInstance;
    public static synchronized SQLiteOpenHelper getmInstance(Context context) {
        if(mInstance == null) {
            mInstance = new MySqliteOpenHelper(context,"xupeng.dp",null,1);

        }
        return mInstance;
    }

    private MySqliteOpenHelper(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        //创建表 表数据初始化
        //id的标准写法
        //主键必须为1
        String sql = "create table persons(_id integer primary key autoincrement, name text)";
        sqLiteDatabase.execSQL(sql);
    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

    }
}

MainActivity.java

package com.example.learning01;
import androidx.appcompat.app.AppCompatActivity;

import android.annotation.SuppressLint;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.Bundle;
import android.util.Log;
import android.view.View;


public class MainActivity extends AppCompatActivity {

    private static final String TAG ="MainActivity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

    }

    public void create_db(View view) {
        SQLiteOpenHelper helper = MySqliteOpenHelper.getmInstance(this);
        //文件夹的创建靠下面这句话
        SQLiteDatabase read = helper.getReadableDatabase();

    }

    public void find_db(View view) {
        SQLiteOpenHelper helper = MySqliteOpenHelper.getmInstance(this);
        SQLiteDatabase db = helper.getReadableDatabase();
        if(db.isOpen()) {
            //返回游标
            Cursor cursor = db.rawQuery("select * from persons", null);

            while (cursor.moveToNext()) {
                @SuppressLint("Range") int _id = cursor.getInt(cursor.getColumnIndex("_id"));
                @SuppressLint("Range") String name = cursor.getString(cursor.getColumnIndex("name"));

                Log.d(TAG, "id: "+_id + "  name :"+name);
            }
            cursor.close();//关闭游标
            db.close();//关闭数据库
        }
    }

    public void insert_db(View view) {
        SQLiteOpenHelper helper = MySqliteOpenHelper.getmInstance(this);
        SQLiteDatabase db = helper.getWritableDatabase();

        if(db.isOpen()){
            String sql = "insert into persons(name) values('xdupeng01')";

            db.execSQL(sql);
        }
        db.close();//关闭数据库
    }

    public void update_db(View view) {
        SQLiteOpenHelper helper = MySqliteOpenHelper.getmInstance(this);
        SQLiteDatabase db = helper.getWritableDatabase();

        if(db.isOpen()){
            String sql = "update persons set name=? where _id=?";

            db.execSQL(sql,new Object[]{"李连杰",5});
        }
        db.close();//关闭数据库
    }

    public void delete_db(View view) {
        SQLiteOpenHelper helper = MySqliteOpenHelper.getmInstance(this);
        SQLiteDatabase db = helper.getWritableDatabase();

        if(db.isOpen()){
            String sql = "delete from persons where _id=?";

            db.execSQL(sql,new Object[]{4});
        }
        db.close();//关闭数据库
    }
}

4、演示效果