为什么即使没有错误我的应用程序也会崩溃（帮助）[重复]

Question

我正在尝试创建一个测验应用程序（尽管我不太擅长使用 android studio）我对代码进行了一些更改并尝试在 android 模拟器上运行该应用程序，但我注意到该应用程序不断崩溃并拒绝在构建应用程序时运行，尽管没有错误。

可能是什么问题，我怎样才能让应用程序在不崩溃的情况下运行？

这是我从事的第一个项目之一，对 java 和 android studio 的了解有限。

package com.myafrica.africaquiz;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.RadioButton;
import android.widget.TextView;


public class MainActivity extends AppCompatActivity {

//Getting the ID of the TextView of the question text
TextView TestQuestionID = (TextView) findViewById(R.id.TestQuestion);

//Getting the ID of the TextView of the question answer
RadioButton AnswerA_ID = (RadioButton) findViewById(R.id.AnswerA);
RadioButton AnswerB_ID = (RadioButton) findViewById(R.id.AnswerB);
RadioButton AnswerC_ID = (RadioButton) findViewById(R.id.AnswerC);
RadioButton AnswerD_ID = (RadioButton) findViewById(R.id.AnswerD);

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
}

public void GetNextQuestion(View view) {
    Question1();

}


    /*
    This part of the code will contain the answer part of this quiz app.
    Each question is a method and that method will be called when the Next 
    button is clicked in the app.
    When the button is clicked the setText() will automatically (re)set the 
    text in the question layout in the XML
     */

public void Question1() {
    TestQuestionID.setText("Which part of Africa can Ghana be located");
    AnswerA_ID.setText(" A: West Africa");
    AnswerB_ID.setText(" B: East Africa");
    AnswerC_ID.setText(" C: Central Africa");
    AnswerD_ID.setText(" D: North Africa");
}
}

这是 myXML 代码

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/ScrollViewLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<RelativeLayout
    android:id="@+id/QuestionViewLayout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="10dp"
            android:text="@string/quiz_progress"
            android:textSize="15sp" />

        <ProgressBar
            style="@style/Widget.AppCompat.ProgressBar.Horizontal"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginEnd="10dp"
            android:layout_marginTop="12dp" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="40dp"
        android:orientation="vertical">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_margin="10dp"
            android:text="Question 1 / 50" />

        <TextView
            android:id="@+id/TestQuestion"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_margin="10dp"
            android:text="How old is james Mother?"
            android:textSize="20sp" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="125dp"
        android:orientation="vertical">

        <RadioGroup
            android:layout_width="wrap_content"
            android:layout_height="wrap_content">

            <RadioButton
                android:id="@+id/AnswerA"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="10dp"
                android:layout_marginTop="10dp"
                android:padding="5dp"
                android:text=" A: 20" />

            <RadioButton
                android:id="@+id/AnswerB"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="10dp"
                android:layout_marginTop="5dp"
                android:padding="5dp"
                android:text=" B: 50" />

            <RadioButton
                android:id="@+id/AnswerC"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="10dp"
                android:layout_marginTop="5dp"
                android:padding="5dp"
                android:text=" B: 100" />

            <RadioButton
                android:id="@+id/AnswerD"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="10dp"
                android:layout_marginTop="5dp"
                android:padding="5dp"
                android:text=" D: 58" />
        </RadioGroup>
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="300dp"
        android:gravity="center"
        android:orientation="horizontal">

        <Button
            android:id="@+id/PreviousButton"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="20dp"
            android:padding="10dp"
            android:text="@string/Previous"
            android:textSize="15sp" />

        <Button
            android:id="@+id/NextButton"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="20dp"
            android:onClick="GetNextQuestion"
            android:padding="10dp"
            android:text="@string/Next"
            android:textSize="15sp" />
    </LinearLayout>
    </RelativeLayout> 
 </ScrollView>

这是来自 Logcat 的详细信息

01-30 14:10:28.606 16454-16454/? I/rica.africaqui: Not late-enabling - 
Xcheck:jni (already on)
01-30 14:10:28.648 16454-16454/? W/rica.africaqui: Unexpected CPU variant 
for X86 using defaults: x86
01-30 14:10:28.832 16454-16454/com.myafrica.africaquiz I/rica.africaqui: 
The ClassLoaderContext is a special shared library.
01-30 14:10:28.992 16454-16454/com.myafrica.africaquiz W/rica.africaqui: 
JIT profile information will not be recorded: profile file does not exits.
01-30 14:10:28.995 16454-16454/com.myafrica.africaquiz I/chatty: 
uid=10086(com.myafrica.africaquiz) identical 10 lines
01-30 14:10:28.995 16454-16454/com.myafrica.africaquiz W/rica.africaqui: 
JIT profile information will not be recorded: profile file does not exits.
01-30 14:10:29.026 16454-16454/com.myafrica.africaquiz I/InstantRun: 
starting instant run server: is main process
01-30 14:10:29.252 16454-16454/com.myafrica.africaquiz D/AndroidRuntime: 
Shutting down VM
01-30 14:10:29.271 16454-16454/com.myafrica.africaquiz E/AndroidRuntime: 
FATAL EXCEPTION: main
Process: com.myafrica.africaquiz, PID: 16454
java.lang.RuntimeException: Unable to instantiate activity 

ComponentInfo{com.myafrica.africaquiz/
com.myafrica.africaquiz.MainActivity}: 
java.lang.NullPointerException: Attempt to invoke virtual method 
'android.view.Window$Callback android.view.Window.getCallback()' on a null 
object reference
    at 
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2843)
    at 
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
    at 

android.app.servertransaction.LaunchActivityItem.execute
(LaunchActivityItem.java:78)
    at 
android.app.servertransaction.TransactionExecutor.executeCallbacks
(TransactionExecutor.java:108)
    at android.app.servertransaction.TransactionExecutor.execute
(TransactionExecutor.java:68)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6669)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run
(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual 
method 'android.view.Window$Callback android.view.Window.getCallback()' 
on a null object reference
    at android.support.v7.app.AppCompatDelegateImplBase.<init> 
(AppCompatDelegateImplBase.java:117)
    at android.support.v7.app.AppCompatDelegateImplV9.<init> 
(AppCompatDelegateImplV9.java:149)
    at android.support.v7.app.AppCompatDelegateImplV14.<init> 
(AppCompatDelegateImplV14.java:56)
    at android.support.v7.app.AppCompatDelegateImplV23.<init> 
(AppCompatDelegateImplV23.java:31)
    at android.support.v7.app.AppCompatDelegateImplN.<init> 
(AppCompatDelegateImplN.java:31)
    at 
android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:198)
    at 
android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:183)
    at 
android.support.v7.app.AppCompatActivity.getDelegate
(AppCompatActivity.java:519)
    at android.support.v7.app.AppCompatActivity.findViewById
(AppCompatActivity.java:190)
    at com.myafrica.africaquiz.MainActivity.<init>(MainActivity.java:13)
    at java.lang.Class.newInstance(Native Method)
    at 
 android.app.AppComponentFactory.instantiateActivity
 (AppComponentFactory.java:69)
    at android.app.Instrumentation.newActivity(Instrumentation.java:1215)
    at 
 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2831)
    at 
 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) 
    at 

 android.app.servertransaction.LaunchActivityItem.execute
 (LaunchActivityItem.java:78) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks
 (TransactionExecutor.java:108) 
    at android.app.servertransaction.TransactionExecutor.execute
 (TransactionExecutor.java:68) 
    at 
 android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) 
    at android.os.Handler.dispatchMessage(Handler.java:106) 
    at android.os.Looper.loop(Looper.java:193) 
    at android.app.ActivityThread.main(ActivityThread.java:6669) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run
 (RuntimeInit.java:493) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 
 01-30 14:10:29.450 16454-16465/com.myafrica.africaquiz I/rica.africaqui: 
 Background concurrent copying GC freed 20027(6MB) AllocSpace objects, 
0(0B) 
LOS 
objects, 58% free, 1102KB/2MB, paused 757us total 159.205ms

虽然我还没有完成应用程序的构建，但我想在遇到这个问题之前对其进行测试并看看结果可能是什么。

Answer 1

您应该在第一步中将 RadioButtons 声明为 null：

RadioButton AnswerA_ID = null;
RadioButton AnswerB_ID = null;
RadioButton AnswerC_ID = null;
RadioButton AnswerD_ID = null;

然后在 OnCreate 你应该这样做：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    AnswerA_ID = (RadioButton) findViewById(R.id.AnswerA);
    AnswerB_ID = (RadioButton) findViewById(R.id.AnswerB);
    AnswerC_ID = (RadioButton) findViewById(R.id.AnswerC);
    AnswerD_ID = (RadioButton) findViewById(R.id.AnswerD);
}