我在尝试访问按钮或 AppCompatEditText 时遇到问题-解网

问：

我尝试使用 findViewById（）函数访问按钮或 AppCompatEditText

Kotlin 代码：

package com.example.qrecycle

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.WindowManager
import android.widget.Button
import android.widget.EditText
import android.widget.Toast
import androidx.appcompat.widget.AppCompatEditText

class RegisterActivity : AppCompatActivity() {

//    val fullNameInput        : AppCompatEditText = findViewById(R.id.editTextFullName)
//    val emailInput           : AppCompatEditText = findViewById(R.id.editTextEmail)
//    val passwordInput        : AppCompatEditText = findViewById(R.id.editTextPassword)
//    val confirmPasswordInput : AppCompatEditText = findViewById(R.id.editTextConfirmPassword)
    override fun onCreate(savedInstanceState: Bundle?) {

        val registerBtn : Button = findViewById(R.id.registerBtn)

        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_register)

        @Suppress("DEPRECATION")
        window.setFlags(
            WindowManager.LayoutParams.FLAG_FULLSCREEN,
            WindowManager.LayoutParams.FLAG_FULLSCREEN
        )

//        Toast.makeText(this, "I WORK!!", Toast.LENGTH_SHORT).show()

        registerBtn.setOnClickListener {
            Toast.makeText(this, "I work", Toast.LENGTH_SHORT).show()
        }

    }

}

XML代码：

<?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"
    android:gravity="center"
    android:background="@drawable/background_gradient"
    tools:context=".RegisterActivity">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:paddingTop="20dp"
        android:paddingBottom="20dp"
        android:layout_marginTop="10dp"
        android:layout_marginBottom="10dp"
        android:fontFamily="@font/montserrat_alternates"
        android:text="@string/registerMsg"
        android:textSize="30sp"
        android:textStyle="bold"
        android:textColor="@color/white" />

    <androidx.cardview.widget.CardView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="20dp"
        android:layout_marginEnd="20dp"
        android:elevation="20dp"
        app:cardBackgroundColor="@color/backgroundColor"
        app:cardCornerRadius="25dp" >
        
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            android:gravity="center" >

            <com.google.android.material.textfield.TextInputLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginStart="20dp"
                android:layout_marginEnd="20dp"
                android:layout_marginTop="20dp"
                android:hint="@string/fullNameText"
                app:endIconMode="clear_text"
                android:textColorHint="@color/blackWithLowerOpacity"
                app:boxBackgroundMode="none">

                <androidx.appcompat.widget.AppCompatEditText
                    android:id="@+id/editTextFullName"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_margin="8dp"
                    android:background="@drawable/shape_edit_text_rounded"
                    android:gravity="start"
                    android:inputType="textCapWords"
                    android:textSize="18sp"
                    tools:ignore="SpeakableTextPresentCheck,VisualLintTextFieldSize" />
            </com.google.android.material.textfield.TextInputLayout>

            <com.google.android.material.textfield.TextInputLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginStart="20dp"
                android:layout_marginEnd="20dp"
                android:hint="@string/emailText"
                app:endIconMode="clear_text"
                android:textColorHint="@color/blackWithLowerOpacity"
                app:boxBackgroundMode="none" >

                <androidx.appcompat.widget.AppCompatEditText
                    android:id="@+id/editTextEmail"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_margin="8dp"
                    android:background="@drawable/shape_edit_text_rounded"
                    android:gravity="start"
                    android:inputType="textEmailAddress"
                    android:textSize="18sp"
                    tools:ignore="SpeakableTextPresentCheck,VisualLintTextFieldSize" />
            </com.google.android.material.textfield.TextInputLayout>

            <com.google.android.material.textfield.TextInputLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginStart="20dp"
                android:layout_marginEnd="20dp"
                android:hint="@string/passwordText"
                app:endIconMode="clear_text"
                android:textColorHint="@color/blackWithLowerOpacity"
                app:boxBackgroundMode="none" >

                <androidx.appcompat.widget.AppCompatEditText
                    android:id="@+id/editTextPassword"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_margin="8dp"
                    android:background="@drawable/shape_edit_text_rounded"
                    android:gravity="start"
                    android:inputType="textPassword"
                    android:textSize="18sp"
                    tools:ignore="SpeakableTextPresentCheck,VisualLintTextFieldSize" />
            </com.google.android.material.textfield.TextInputLayout>

            <com.google.android.material.textfield.TextInputLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginStart="20dp"
                android:layout_marginEnd="20dp"
                android:layout_marginBottom="20dp"
                android:hint="@string/confirmPasswordText"
                app:endIconMode="clear_text"
                android:textColorHint="@color/blackWithLowerOpacity"
                app:boxBackgroundMode="none" >

                <androidx.appcompat.widget.AppCompatEditText
                    android:id="@+id/editTextConfirmPassword"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_margin="8dp"
                    android:background="@drawable/shape_edit_text_rounded"
                    android:gravity="start"
                    android:inputType="textPassword"
                    android:textSize="18sp"
                    tools:ignore="SpeakableTextPresentCheck,VisualLintTextFieldSize" />
            </com.google.android.material.textfield.TextInputLayout>

            <Button
                android:id="@+id/registerBtn"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginStart="30dp"
                android:layout_marginEnd="30dp"
                android:layout_marginTop="10dp"
                android:layout_marginBottom="40dp"
                android:background="@drawable/shape_button_dark_blue_rounded"
                android:fontFamily="@font/lobster"
                android:letterSpacing=".05"
                android:textSize="22sp"
                android:text="@string/registerBtnText"
                android:textColor="@color/white"
                android:textAllCaps="false"
                tools:ignore="VisualLintButtonSize" />

        </LinearLayout>

    </androidx.cardview.widget.CardView>

</LinearLayout>

当我尝试运行我的应用程序并进入该活动时，应用程序崩溃，我收到此错误：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.qrecycle, PID: 14505
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.qrecycle/com.example.qrecycle.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:3682)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3942)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:109)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2345)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loopOnce(Looper.java:233)
        at android.os.Looper.loop(Looper.java:344)
        at android.app.ActivityThread.main(ActivityThread.java:8212)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:584)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1034)
     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:191)
        at android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:174)
        at android.content.Context.obtainStyledAttributes(Context.java:804)
        at androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor(AppCompatDelegateImpl.java:922)
        at androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor(AppCompatDelegateImpl.java:889)

        at androidx.appcompat.app.AppCompatDelegateImpl.findViewById(AppCompatDelegateImpl.java:691)
        at androidx.appcompat.app.AppCompatActivity.findViewById(AppCompatActivity.java:264)
        at com.example.qrecycle.RegisterActivity.<init>(RegisterActivity.kt:13)
        at java.lang.Class.newInstance(Native Method)
        at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:95)
        at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:45)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1288)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3669)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3942) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:109) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2345) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loopOnce(Looper.java:233) 
        at android.os.Looper.loop(Looper.java:344) 
        at android.app.ActivityThread.main(ActivityThread.java:8212) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:584) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1034) 
I/Process: Sending signal. PID: 14505 SIG: 9

我还收到以下消息：

V/AutofillManager: requestHideFillUi(null): anchor = null
V/AutofillManager: requestHideFillUi(null): anchor = null
V/TextView: notifyAutoFillManagerAfterTextChanged
V/AutofillManager: notifyValueChanged(1073741824): ignoring on state UNKNOWN

多次

我是 android 开发的新手，所以欢迎任何让我的代码更好的评论。

我试过这些：

private lateinit val fullNameInput : AppCompatEditText

val fullNameInputString = fullNameInput.text.toString()

val fullNameInput : AppCompatEditText = findViewById(R.id.editTextFullName)

private val fullNameInput : AppCompatEditText = findViewById(R.id.editTextFullName)

Android Kotlin 移动 null

答：

0赞 Zapbroob 4/9/2023 #1

问题是，在调用“setContentView（）”方法之前，您正在尝试访问属于“View”类的UI元素。您可以在 setContentView（）方法之前执行所需的任何代码，只是它不引用尚未设置的 View（部分）。因此，请在调用“setContentView（）”后尝试使用“findViewById（）”方法。

0赞 George_Sari 4/9/2023

我尝试了您的解决方案，但仍然有完全相同的问题。谢谢

0赞 Zapbroob 4/10/2023

请确保在清单文件中使用正确的包名称和活动名称正确声明 RegisterActivity。

0赞 George_Sari 4/10/2023

在使用注释掉变量进行调试后，我发现此问题仅在 emailTextInput 变量未注释时发生，而我仍然没有弄清楚为什么会发生这种情况

上一个：MylocationCountry 值如何显示在 Text（）应用栏中？

下一个：React 模块解析失败：非 null 断言运算符上的意外令牌

我在尝试访问按钮或 AppCompatEditText 时遇到问题

I have a problem when trying to access a button or an AppCompatEditText

评论

评论