Android开发 练习使用SQLite

    实现一个使用SQLite增删改查数据的小例子，点击按钮执行相关操作。

    MySqlieHelper是创建数据库的类:

package com.engineer.shizhibin.sqlitedemo;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
/**
 * Created by 13922 on 2018/6/10.
 */

public class MySqliteHelper extends SQLiteOpenHelper {
    public MySqliteHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }
    public MySqliteHelper(Context context) {
        super(context,Constant.DB_NAME,null, Constant.DB_VERSION);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        String sql = "create table student (id integer primary key,name varchar(10),age integer)";
        db.execSQL(sql);
    }

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

    }
}

Constant是保存常量的类：

package com.engineer.shizhibin.sqlitedemo;

/**
 * Created by 13922 on 2018/6/10.
 */

public class Constant {
    public static final String DB_NAME = "db_info";
    public static final int DB_VERSION = 1;
    public static final String TB_NAME= "user";
}

为了解耦，不在MainActivity中直接操作数据库。使用DbManager类进行相关操作：

package com.engineer.shizhibin.sqlitedemo;

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

/**
 * Created by 13922 on 2018/6/10.
 */

public class DbManager {
    private static MySqliteHelper helper;

    public static MySqliteHelper getInstance(Context context) {
        if (helper == null) {
            helper = new MySqliteHelper(context);
        }
        return helper;
    }
    public static void execSql(SQLiteDatabase db,String sql) {
        if(db != null && !"".equals(sql)) {
            db.execSQL(sql);
        }
    }
    public static Cursor query(SQLiteDatabase db,String sql) {
        Cursor c = db.rawQuery(sql,null);
        return c;
    }
}

MainActivity类：

package com.engineer.shizhibin.sqlitedemo;

import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {
    private MySqliteHelper helper;
    private TextView tv_result;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        helper = DbManager.getInstance(this);
        tv_result = this.findViewById(R.id.result);
    }
    public void createDb(View view) {
        SQLiteDatabase db = helper.getReadableDatabase();
    }
    public void click(View view) {
        StringBuffer result = new StringBuffer("");
        switch (view.getId()) {
            case R.id.insert:
                SQLiteDatabase db = helper.getReadableDatabase();
                String sql = "insert into student values(1,'Tom',21)";
                String sql2 = "insert into student values(2,'Bob',20)";
                DbManager.execSql(db,sql);
                DbManager.execSql(db,sql2);
                db.close();
                break;
            case R.id.update:
                db = helper.getReadableDatabase();
                String update = "update student set name ='Jack' where id = 2";
                DbManager.execSql(db,update);
                result.delete(0,result.length());
                db.close();
                break;
            case R.id.delete:
                db = helper.getReadableDatabase();
                String delete = "delete from student where id = 2";
                DbManager.execSql(db,delete);
                result.delete(0,result.length());
                db.close();
                break;
            case R.id.query:
                db = helper.getReadableDatabase();
                String query = "select * from student";
                Cursor c = DbManager.query(db,query);
                while(c.moveToNext()) {
                    int id = c.getInt(0);
                    String name = c.getString(1);
                    int age = c.getInt(2);
                    result.append(id).append(name).append(age);
                }
                tv_result.setText(result);
                db.close();
                break;
        }
    }
}

.xml文件：

程序效果：

1.点击创建数据库，并点击插入数据，然后查询数据：

有两个学生信息，1号 Tom 21岁 2号 Bob 20岁

2.点击修改，查询 Bob被改成了Jack：

3.点击删除，查询只剩下了1号同学：