Android开发之sqlite数据库(小白)

Android开发之sqlite数据库

效果：sqlite的创建，增删改查 3步走：配置文件AndroidManifest.xml无改动，此处不展示。

import android.content.Context;

import android.database.Cursor;

import android.database.sqlite.SQLiteDatabase;

import android.database.sqlite.SQLiteOpenHelper;

import android.text.Editable;

import android.util.Log;

import android.view.View;

import android.widget.Button;

import android.widget.EditText;

import android.widget.TextView;

import android.widget.Toast;

import androidx.annotation.Nullable;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

/**

* 建立sqlite数据库，进行用户名和密码的存储

*/

public class MainActivity extends AppCompatActivity implements View.OnClickListener{

//编辑框，输入

EditText username;

EditText password;

EditText selectuser;

//结果文本框

TextView result;

//3个按钮

Button buttonadd;

Button buttondelete;

Button buttonselect;

//帮助建立sqlite数据库

SQLiteOpenHelper mysqlhelper;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

init();

buttonadd.setOnClickListener(this);

buttondelete.setOnClickListener(this);

buttonselect.setOnClickListener(this);

}

public void init(){

username = findViewById(R.id.username);

password = findViewById(R.id.password);

selectuser = findViewById(R.id.selectuser);

result = findViewById(R.id.result);

buttonadd = findViewById(R.id.buttonadd);

buttondelete = findViewById(R.id.buttondelete);

buttonselect = findViewById(R.id.buttonselect);

// mysqlhelper = new MyDBHelper(MainActivity.this, "MyDatabase.db", null, 666);

// //SQLiteDatabase db = mysqlhelper.getWritableDatabase();

}

@Override

public void onClick(View v) {

mysqlhelper = new MyDBHelper(MainActivity.this, "MyDatabase.db", null, 666);

SQLiteDatabase db;

String username1 = null;

String password1 = null;

Log.v("start","按钮事件：");

switch(v.getId()){

case R.id.buttonadd:

db = mysqlhelper.getWritableDatabase();

username1 = username.getText().toString();

password1 = password.getText().toString();

if(username1==null&&username1==""&&username1==" "){

Toast.makeText(MainActivity.this,"用户名不能为空",Toast.LENGTH_LONG).show();

Log.v("start","添加失败");

}else if(password1==null){

Toast.makeText(MainActivity.this,"密码不能为空",Toast.LENGTH_LONG).show();

}else {

db.execSQL("insert into user(username,password) values(?,?)", new Object[]{username1, password1});

Toast.makeText(MainActivity.this,"添加成功",Toast.LENGTH_LONG).show();

result.setText("查询结果为：");

result.append("用户名"+username1+"密码"+password1);

}

db.close();

break;

case R.id.buttondelete:

db = mysqlhelper.getWritableDatabase();

String usernamed = selectuser.getText().toString();

db.execSQL("delete from user where username=?",new Object[]{usernamed});

db.close();

Toast.makeText(MainActivity.this,"删除成功",Toast.LENGTH_LONG).show();

break;

case R.id.buttonselect:

result.setText("查询结果为：");

db = mysqlhelper.getWritableDatabase();

Cursor cursor = db.rawQuery("select * from user", null);

while (cursor.moveToNext()){

result.append("\n" + "第" + cursor.getInt(0) +

"，用户名：" + cursor.getString(1) +

",密码是：" + cursor.getString(2));

}

cursor.close();

db.close();

Toast.makeText(MainActivity.this,"查询成功",Toast.LENGTH_LONG).show();

Log.v("start","查询成功");

break;

}

}

/**

* sqlite数据库创建帮助类

*/

public class MyDBHelper extends SQLiteOpenHelper{

public MyDBHelper(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {

super(context, name, factory, version);

}

@Override

public void onCreate(SQLiteDatabase db) {

db.execSQL("CREATE TABLE user(" +

"user_id INTEGER PRIMARY KEY AUTOINCREMENT," +

"username VARCHAR(20),"+

"password VARCHAR(20)"+

")");

}

@Override

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

}

}

}

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:gravity="center"

android:orientation="vertical"

tools:context=".MainActivity">

android:layout_gravity="center"

android:background="@mipmap/ic_launcher"

android:layout_width="100dp"

android:layout_height="100dp">

android:id="@+id/username"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:hint="请输入用户名">

android:id="@+id/password"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:inputType="textPassword"

android:hint="输入密码">

android:id="@+id/selectuser"

android:layout_width="match_parent" android:layout_height="wrap_content"

android:hint="目标用户">

android:id="@+id/result"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="查询结果"

android:textSize="25sp"

>

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:orientation="horizontal"

>

android:id="@+id/buttonadd"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="wrap_content"

android:text="添加">

android:id="@+id/buttondelete"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="wrap_content"

android:text="删除">

android:id="@+id/buttonselect"

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="wrap_content"

android:text="查询">

More1:sqlite在哪看数值

在屏幕左侧View栏选择Tool Windows，就可以看到Device File Explorer。于是我们就得到了屏幕右侧的Device File Explorer，在data中的data中的com.example.项目名中，找到database中的db文件，将它导入到Navicat数据库管理工具中即可查看具体数据。

More2: 设计模式（代码处的巧妙之处）

下面这个implements View.OnClickListener有什么用呢：它将MainActivity变成它，在按钮监听的时候就不用每(1)次都去new了，巧妙利用选择switch语句（n)。

好文链接