無法實例化活動ComponentInfo空指針異常

Question

每當我使用com4j庫打開一個活動時，我都會崩潰。這是錯誤代碼：

10-08 16:10:32.615: E/AndroidRuntime(18210): FATAL EXCEPTION: main 
10-08 16:10:32.615: E/AndroidRuntime(18210): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.twotowersstudios.quizmaker/com.twotowersstudios.quizmaker.MakeQuizActivity}: java.lang.NullPointerException 
10-08 16:10:32.615: E/AndroidRuntime(18210): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2024) 
10-08 16:10:32.615: E/AndroidRuntime(18210): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2125) 
10-08 16:10:32.615: E/AndroidRuntime(18210): at android.app.ActivityThread.access$600(ActivityThread.java:140) 
10-08 16:10:32.615: E/AndroidRuntime(18210): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1227) 
10-08 16:10:32.615: E/AndroidRuntime(18210): at android.os.Handler.dispatchMessage(Handler.java:99) 
10-08 16:10:32.615: E/AndroidRuntime(18210): at android.os.Looper.loop(Looper.java:137) 
10-08 16:10:32.615: E/AndroidRuntime(18210): at android.app.ActivityThread.main(ActivityThread.java:4898) 
10-08 16:10:32.615: E/AndroidRuntime(18210): at java.lang.reflect.Method.invokeNative(Native Method) 
10-08 16:10:32.615: E/AndroidRuntime(18210): at java.lang.reflect.Method.invoke(Method.java:511) 
10-08 16:10:32.615: E/AndroidRuntime(18210): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1006) 
10-08 16:10:32.615: E/AndroidRuntime(18210): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:773) 
10-08 16:10:32.615: E/AndroidRuntime(18210): at dalvik.system.NativeStart.main(Native Method) 
10-08 16:10:32.615: E/AndroidRuntime(18210): Caused by: java.lang.NullPointerException 
10-08 16:10:32.615: E/AndroidRuntime(18210): at android.app.Activity.findViewById(Activity.java:1882) 
10-08 16:10:32.615: E/AndroidRuntime(18210): at com.twotowersstudios.quizmaker.MakeQuizActivity.<init>(MakeQuizActivity.java:44) 
10-08 16:10:32.615: E/AndroidRuntime(18210): at java.lang.Class.newInstanceImpl(Native Method) 
10-08 16:10:32.615: E/AndroidRuntime(18210): at java.lang.Class.newInstance(Class.java:1319) 
10-08 16:10:32.615: E/AndroidRuntime(18210): at android.app.Instrumentation.newActivity(Instrumentation.java:1057) 
10-08 16:10:32.615: E/AndroidRuntime(18210): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2015) 
10-08 16:10:32.615: E/AndroidRuntime(18210): ... 11 more 

這是崩潰類：

package com.twotowersstudios.quizmaker; 

import java.io.FileWriter; 
import java.io.IOException; 

import org.dom4j.Document; 
import org.dom4j.DocumentHelper; 
import org.dom4j.Element; 
import org.dom4j.io.XMLWriter; 

import android.app.Activity; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.View; 
import android.widget.EditText; 
import android.widget.RadioButton; 

public class MakeQuizActivity extends Activity { 
    /**String filename = "Question1.xml"; 
    String string = ""; 
    FileOutputStream outputStream; 
    * @return */ 
    private RadioButton JRQ1A1; 
    private RadioButton JRQ1A2; 
    private RadioButton JRQ1A3; 
    private RadioButton JRQ1A4; 
    private String rightAnswerValue; 



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

     } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.make_quiz, menu); 
     return true; 
    } 
    EditText Q1 = (EditText)findViewById(R.id.Q1Actual); 
    EditText Q1A1 = (EditText)findViewById(R.id.Q1A1); 
    EditText Q1A2 = (EditText)findViewById(R.id.Q1A2); 
    EditText Q1A3 = (EditText)findViewById(R.id.Q1A3); 
    EditText Q1A4 = (EditText)findViewById(R.id.Q1A4); 
    String Q1Str = Q1.getText().toString(); 
    String Q1A1Str = Q1A1.getText().toString(); 
    String Q1A2Str = Q1A2.getText().toString(); 
    String Q1A3Str = Q1A3.getText().toString(); 
    String Q1A4Str = Q1A4.getText().toString(); 

    public void rightAnswerSelection (View view){ 
     if (JRQ1A1.isChecked()){ 
      rightAnswerValue = "@id/Q1A1"; 
     }else if (JRQ1A2.isChecked()){ 
      rightAnswerValue = "@id/Q1A2"; 
     }else if (JRQ1A3.isChecked()){ 
      rightAnswerValue = "@id/Q1A3"; 
     }else if (JRQ1A4.isChecked()){ 
      rightAnswerValue = "@id/Q1A4"; 
     } 
    } 
    public void createXML() throws IOException { 
     if (JRQ1A1.isChecked()){ 
      rightAnswerValue = "@id/Q1A1"; 
     }else if (JRQ1A2.isChecked()){ 
      rightAnswerValue = "@id/Q1A2"; 
     }else if (JRQ1A3.isChecked()){ 
      rightAnswerValue = "@id/Q1A3"; 
     }else if (JRQ1A4.isChecked()){ 
      rightAnswerValue = "@id/Q1A4"; 
     } 
     Document document = DocumentHelper.createDocument(); 
     Element rootElement = document.addElement("Questions"); 
     Element studentElement = rootElement.addElement("Question1").addAttribute("rightanswer", rightAnswerValue); 
     studentElement.addElement("Q1").addText(Q1Str); 
     studentElement.addElement("Q1A1").addText(Q1A1Str); 
     studentElement.addElement("Q1A2").addText(Q1A2Str); 
     studentElement.addElement("Q1A3").addText(Q1A3Str); 
     studentElement.addElement("Q1A4").addText(Q1A4Str); 
     studentElement.addElement("name").addText("Peter"); 
     XMLWriter writer = new XMLWriter(new FileWriter("Students.xml")); 
     //Note that You can format this XML document 
     /* 
     * FileWriter output = new FileWriter(new File("Students.xml")); 
     OutputFormat format = OutputFormat.createPrettyPrint(); 
     XMLWriter writer = new XMLWriter(output,format);<- will fomat the output 
     */ 

     //You can print this to the console and see what it looks like 
     String xmlElement = document.asXML(); 
     System.out.println(xmlElement); 
     writer.write(document); 
     writer.close(); 

    } 

} 

Android清單：

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 

    package="com.twotowersstudios.quizmaker" 
    android:versionCode="1" 
    android:versionName="1.0" > 

    <uses-sdk 
     android:minSdkVersion="11" 
     android:targetSdkVersion="18" /> 
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> 

    <application 
     android:allowBackup="true" 
     android:icon="@drawable/ic_launcher" 
     android:label="@string/app_name" 
     android:theme="@style/AppTheme" > 

     <activity 
      android:name="com.twotowersstudios.quizmaker.MainTitleScreen" 
      android:label="@string/app_name" > 
      <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 

       <category android:name="android.intent.category.LAUNCHER" /> 
      </intent-filter> 
     </activity> 
     <activity 
      android:name="com.twotowersstudios.quizmaker.ReportABugActivity" 
      android:label="@string/title_activity_report_abug" 
      android:parentActivityName="com.twotowersstudios.quizmaker.MainTitleScreen" > 
     </activity> 
     <activity 
      android:name="com.twotowersstudios.quizmaker.MakeQuizActivity" 
      android:label="@string/title_activity_make_quiz" 
      android:parentActivityName="com.twotowersstudios.quizmaker.MainTitleScreen" > 
     </activity> 
    </application> 

</manifest> 

最後，整個項目：https://github.com/coldblade2000/QuizMaker

Answer 1

我不是一名android開發者，但我的猜測是你必須移動你的代碼：

EditText Q1 = (EditText)findViewById(R.id.Q1Actual); 
EditText Q1A1 = (EditText)findViewById(R.id.Q1A1); 
EditText Q1A2 = (EditText)findViewById(R.id.Q1A2); 
EditText Q1A3 = (EditText)findViewById(R.id.Q1A3); 
EditText Q1A4 = (EditText)findViewById(R.id.Q1A4); 
String Q1Str = Q1.getText().toString(); 
String Q1A1Str = Q1A1.getText().toString(); 
String Q1A2Str = Q1A2.getText().toString(); 
String Q1A3Str = Q1A3.getText().toString(); 
String Q1A4Str = Q1A4.getText().toString(); 

的方法例如內部，內部的onCreate（）