Android(Kotlin)应用连接本地MySQL数据库失败求助

我是Android应用开发新手，用Kotlin编写代码，现在要实现应用连接本地MySQL所在电脑的服务器，完成用户注册数据提交和登录功能，但点击注册按钮完全没反应。已有网站能正常连接该本地服务器和数据库，以下是相关代码：

Dbhelper.kt #

package com.example.myapplication

import java.sql.Connection
import java.sql.DriverManager
import java.sql.ResultSet
import java.sql.SQLException

class Dbhelper(private val url: String, private val user: String, private val password: String) {
    init {
        try {
            Class.forName("com.mysql.cj.jdbc.Driver")
        } catch (e: ClassNotFoundException) {
            e.printStackTrace()
        }
    }

    fun connect(): Connection? {
        try {
            return DriverManager.getConnection(url, user, password)
        } catch (e: SQLException) {
            e.printStackTrace()
        }
        return null
    }

    fun isUserExists(login: String, email: String): Boolean {
        connect()?.use { connection ->
            val query = "SELECT * FROM appmovie_users WHERE login = ? OR email = ?"
            val preparedStatement = connection.prepareStatement(query)
            preparedStatement.setString(1, login)
            preparedStatement.setString(2, email)
            val resultSet: ResultSet = preparedStatement.executeQuery()
            return resultSet.next()
        }
        return false
    }

    fun addUser(login: String, email: String, password: String): Boolean {
        connect()?.use { connection ->
            val query = "INSERT INTO appmovie_users (login, email, password) VALUES (?, ?, ?)"
            val preparedStatement = connection.prepareStatement(query)
            preparedStatement.setString(1, login)
            preparedStatement.setString(2, email)
            preparedStatement.setString(3, password)
            val rowsAffected = preparedStatement.executeUpdate()
            return rowsAffected > 0
        }
        return false
    }
}

RegistrationActivity.kt #

package com.example.myapplication 
                                                          
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button
import android.widget.EditText
import android.widget.TextView
import android.widget.Toast
import androidx.lifecycle.ViewModelProvider

class RegistrationActivity : AppCompatActivity() {

    private lateinit var viewModel: RegistrationViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.registration)

        val userLogin = findViewById<EditText>(R.id.user_login)
        val userEmail = findViewById<EditText>(R.id.user_email)
        val userPass = findViewById<EditText>(R.id.user_pass)
        val button = findViewById<Button>(R.id.button_reg)
        val linkToAuth = findViewById<TextView>(R.id.link_to_auth)
        val logoName = findViewById<TextView>(R.id.logoName)

        val dbUrl = "jdbc:mysql://localhost:3306/database-users-movieapp"
        val dbUser = "root"
        val dbPassword = ""

        val dbHelper = Dbhelper(dbUrl, dbUser, dbPassword)

        viewModel = ViewModelProvider(this)[RegistrationViewModel::class.java]

        button.setOnClickListener {
            val login = userLogin.text.toString().trim()
            val email = userEmail.text.toString().trim()
            val pass = userPass.text.toString().trim()

            if (login == "" || email == "" || pass == "") {
                Toast.makeText(this, "Not all fields are filled", Toast.LENGTH_LONG).show()
            } else {
                if (dbHelper.isUserExists(login, email)) {
                    Toast.makeText(this, "User with the same login or email already exists", Toast.LENGTH_LONG).show()
                } else {
                    viewModel.registerUser(login, email, pass)
                }
            }
        }
    }
}

RegistrationViewModel.kt #

package com.example.myapplication

import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.launch

class RegistrationViewModel : ViewModel() {
    private val DB_URL = "jdbc:mysql://localhost:3306/database-users-movieapp"
    private val DB_USER = "root"
    private val DB_PASSWORD = ""

    private val databaseHelper = Dbhelper(DB_URL, DB_USER, DB_PASSWORD)

    val registrationResult = MutableLiveData<Boolean>()

    fun registerUser(login: String, email: String, password: String) {
        viewModelScope.launch(Dispatchers.IO) {
            val isRegistrationSuccessful = databaseHelper.addUser(login, email, password)
            registrationResult.postValue(isRegistrationSuccessful)
        }
    }
}

问题排查与解决方案 #

1. 主线程执行耗时操作导致阻塞

isUserExists方法直接在主线程调用数据库连接和查询，Android禁止主线程执行耗时操作，会触发ANR（应用无响应），导致按钮点击后无反馈。

解决：
将用户存在性检查移到协程中执行：

// 修改RegistrationActivity的按钮点击事件
button.setOnClickListener {
    val login = userLogin.text.toString().trim()
    val email = userEmail.text.toString().trim()
    val pass = userPass.text.toString().trim()

    if (login.isEmpty() || email.isEmpty() || pass.isEmpty()) {
        Toast.makeText(this, "请填写所有字段", Toast.LENGTH_LONG).show()
    } else {
        lifecycleScope.launch(Dispatchers.IO) {
            val exists = dbHelper.isUserExists(login, email)
            launch(Dispatchers.Main) {
                if (exists) {
                    Toast.makeText(this@RegistrationActivity, "该登录名或邮箱已存在", Toast.LENGTH_LONG).show()
                } else {
                    viewModel.registerUser(login, email, pass)
                }
            }
        }
    }
}

需确保Activity依赖协程库，并添加导入：import kotlinx.coroutines.launch、import kotlinx.coroutines.Dispatchers。

2. 本地MySQL连接地址错误

Android设备/模拟器的localhost指向自身，而非运行MySQL的电脑。需替换为电脑的本地IP地址（如192.168.xxx.xxx），同时确保MySQL允许远程连接、防火墙开放3306端口。

修改连接URL：

// 替换为你的电脑本地IP，添加必要参数
val dbUrl = "jdbc:mysql://192.168.1.100:3306/database-users-movieapp?useSSL=false&serverTimezone=UTC"

3. 未监听注册结果反馈

ViewModel的registrationResult已发送注册状态，但Activity未监听，导致成功/失败都无提示，看起来像无响应。

添加结果监听：
在RegistrationActivity的onCreate方法中添加：

viewModel.registrationResult.observe(this) { success ->
    if (success) {
        Toast.makeText(this, "注册成功", Toast.LENGTH_LONG).show()
        // 可跳转至登录页面
    } else {
        Toast.makeText(this, "注册失败，请重试", Toast.LENGTH_LONG).show()
    }
}

4. 额外安全提示

当前代码直接存储明文密码，存在安全风险，建议使用SHA-256或BCrypt加密后再存入数据库。

内容的提问来源于stack exchange，提问作者nothin7