Firebase kotlin android studio 应用程序在第二次活动时崩溃

Question

我正在关注这个 youtube 教程 (https://www.youtube.com/watch?v=0hkyXuKTFYY)，但发生了以下情况。对于视频中的他来说，在 6 点 30 分，他的应用程序也崩溃了，但他在视频中稍后解决了这个问题。对我来说，似乎没有任何效果。

请帮忙！

这是我的日志：

12-09 19:36:45.321 28337-28337/? E/Zygote: v2
12-09 19:36:45.331 28337-28337/? E/Zygote: accessInfo : 0
12-09 19:36:47.831 28337-28337/konark.studios.ourtimetable E/AndroidRuntime: FATAL EXCEPTION: main
    Process: konark.studios.ourtimetable, PID: 28337
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{konark.studios.ourtimetable/konark.studios.ourtimetable.RegisterActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3132)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)
        at android.app.ActivityThread.access$1100(ActivityThread.java:229)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:148)
        at android.app.ActivityThread.main(ActivityThread.java:7325)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
        at android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:162)
        at android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:109)
        at android.content.Context.obtainStyledAttributes(Context.java:514)
        at androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor(AppCompatDelegateImpl.java:839)
        at androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor(AppCompatDelegateImpl.java:806)
        at androidx.appcompat.app.AppCompatDelegateImpl.findViewById(AppCompatDelegateImpl.java:630)
        at androidx.appcompat.app.AppCompatActivity.findViewById(AppCompatActivity.java:223)
        at konark.studios.ourtimetable.RegisterActivity.<init>(RegisterActivity.kt:20)
        at java.lang.Class.newInstance(Native Method)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1096)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3122)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415) 
        at android.app.ActivityThread.access$1100(ActivityThread.java:229) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:148) 
        at android.app.ActivityThread.main(ActivityThread.java:7325) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 

第一个 Activity 照常打开：## Heading ## enter image description here

当我按下创建帐户按钮（在底部）时，它应该移动到第二个活动。但不幸的是，它崩溃了。

第二个活动的代码（即崩溃）：

package konark.studios.ourtimetable

import android.content.Context
import android.content.Intent
import android.os.Bundle
import android.util.Patterns
import android.view.WindowManager
import android.widget.Button
import android.widget.EditText
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import com.google.firebase.auth.FirebaseAuth
import com.google.firebase.auth.ktx.auth
import com.google.firebase.ktx.Firebase

class RegisterActivity : AppCompatActivity() {

    var registerBtn = findViewById<Button>(R.id.RegisterButton)
    var usernamebox = findViewById<EditText>(R.id.emailbox)
    var passwordbox = findViewById<EditText>(R.id.passwordbox)
    val intentLoginActivity = Intent(this, LoginActivity::class.java)
    private lateinit var auth: FirebaseAuth

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        window.setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN)
        setContentView(R.layout.activity_register)
        supportActionBar?.hide();
        auth = Firebase.auth

        registerBtn.setOnClickListener {
            signUpUser()
        }
    }

    private fun signUpUser() {

        if (usernamebox.text.toString().isEmpty()) {
            usernamebox.error = "Please enter your email"
            usernamebox.requestFocus()
            return
        }

        if (Patterns.EMAIL_ADDRESS.matcher(usernamebox.text.toString()).matches()) {
            usernamebox.error = "Please enter a valid email"
            usernamebox.requestFocus()
            return
        }

        if (passwordbox.text.toString().isEmpty()) {
            passwordbox.error = "Please enter a password"
            passwordbox.requestFocus()
            return
        }

        auth.createUserWithEmailAndPassword(usernamebox.text.toString(), passwordbox.text.toString())
                .addOnCompleteListener(this) { task ->
                    if (task.isSuccessful) {
                        startActivity(Intent(intentLoginActivity))
                    } else {
                        Toast.makeText(baseContext, "Authentication failed",
                                Toast.LENGTH_SHORT).show()
                    }
                }
    }
}

这是第一个作为主屏幕的活动的代码：

package konark.studios.ourtimetable

import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.provider.AlarmClock.EXTRA_MESSAGE
import android.util.Log
import android.view.Window
import android.view.WindowManager
import android.widget.Button
import com.google.firebase.auth.FirebaseAuth
import com.google.firebase.auth.FirebaseUser
import com.google.firebase.auth.ktx.auth
import com.google.firebase.ktx.Firebase

class LoginActivity : AppCompatActivity() {

    private lateinit var auth: FirebaseAuth

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        window.setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN)
        setContentView(R.layout.activity_login)
        supportActionBar?.hide();
        auth = Firebase.auth

        var createAccountBtn = findViewById<Button>(R.id.AccountCreation)
        val intentAccountCreate = Intent(this, RegisterActivity::class.java)
        createAccountBtn.setOnClickListener {
            Log.d("Action","Register Button Clicked")
            startActivity(intentAccountCreate)
            finish()
        }
    }

    public override fun onStart() {
        super.onStart()
        // Check if user is signed in (non-null) and update UI accordingly.
        val currentUser = auth.currentUser
        updateUI(currentUser)
    }

    private fun updateUI(currentUser: FirebaseUser?) {

    }
}

Answer 1

var registerBtn = findViewById<Button>(R.id.RegisterButton)
var usernamebox = findViewById<EditText>(R.id.emailbox)
var passwordbox = findViewById<EditText>(R.id.passwordbox)
val intentLoginActivity = Intent(this, LoginActivity::class.java)

将这些函数调用从属性初始值设定项移至onCreate() 函数。

在初始化阶段，将Activity 用作Context 或设置活动窗口以便调用findViewById() 还为时过早。 （同样在setContentView() 之前，你只会得到空值。）

Answer 2

首先确保您的 Activity 在您的 AndroidManifest 文件中声明。 那就试试吧：

createAccountBtn.setOnClickListener {
    val intentAccountCreate = Intent(context, RegisterActivity::class.java)
    Log.d("Action","Register Button Clicked")
    startActivity(intentAccountCreate)
    finish()
}

尝试按以下方式进行