Android应用程序中的NullPointerException（Bundle？）

时间：2016-03-02 14:51:10

标签： java android nullpointerexception

在我正在学习的课程中，我们一直在学习一些Android应用程序开发等等，而且我设法遇到了一个问题，我，对于我的生活，无法弄明白......

基本背景......

旋转设备时出现nullpointerexception ...此错误位于QuizActivity的第100行.....

这一行是：mCheatButton.setOnClickListener(new View.OnClickListener() {//....

我怀疑这与存储或检索捆绑包中的信息有关...

无论如何，这里是代码的其余部分......

这是我的测验活动...对不起所有的代码块，我真的不知道更好的方式来给你这些信息，或者如果你甚至需要所有这些......但是现在我只是可以想象发生了什么...所以我打印了错误（堆栈跟踪？我认为这是正确的术语......）..这里也是...... 

    03-02 09:49:28.858 7921-7921/com.example.ryan.ryans_quiz E/AndroidRuntime: FATAL EXCEPTION: main
                                                                       Process: com.example.ryan.ryans_quiz, PID: 7921
                                                                       java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ryan.ryans_quiz/com.example.ryan.ryans_quiz.QuizActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                           at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                                                                           at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                                                                           at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                                                                           at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                           at android.os.Looper.loop(Looper.java:148)
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                           at java.lang.reflect.Method.invoke(Native Method)
                                                                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                        Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                           at com.example.ryan.ryans_quiz.QuizActivity.onCreate(QuizActivity.java:100)
                                                                           at android.app.Activity.performCreate(Activity.java:6237)
                                                                           at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
                                                                           at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
                                                                           at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                                                                           at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                                           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                                                                           at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                           at android.os.Looper.loop(Looper.java:148) 
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5417) 
                                                                           at java.lang.reflect.Method.invoke(Native Method) 
                                                                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

QuizActivity 

  package com.example.ryan.ryans_quiz;

  import android.app.Activity;
  import android.content.Intent;
  import android.os.Bundle;
  import android.support.v7.app.AppCompatActivity;
  import android.util.Log;
  import android.view.View;
  import android.widget.Button;
  import android.widget.ImageButton;
  import android.widget.TextView;
  import android.widget.Toast;

  public class QuizActivity extends AppCompatActivity {

private static final String TAG = "QuizActivity";
private static final String KEY_INDEX = "index";
private static final int REQUEST_CODE_CHEAT = 0;

private Button mTrueButton;
private Button mFalseButton;
private ImageButton mNextButton;
private Button mCheatButton;
private TextView mQuestionTextView;

private Question[] mQuestionBank = new Question[] {
        new Question(R.string.question_oceans, true),
        new Question(R.string.question_mideast, false),
        new Question(R.string.question_africa, false),
        new Question(R.string.question_americas, true),
        new Question(R.string.question_asia, true)
};

private int mCurrentIndex = 0;

private boolean mIsCheater;

private void updateQuestion() {
    int question = mQuestionBank[mCurrentIndex].getTextResId();
    mQuestionTextView.setText(question);
}

private void checkAnswer(boolean userPressedTrue) {
    boolean answerIsTrue = mQuestionBank[mCurrentIndex].isAnswerTrue();

    int messageResId = 0;

    if (mIsCheater) {
        messageResId = R.string.judgment_toast;
    } else {
        if (userPressedTrue == answerIsTrue) {
            messageResId = R.string.correct_toast;
        } else {
            messageResId = R.string.incorrect_toast;
        }
    }

    Toast.makeText(this, messageResId, Toast.LENGTH_SHORT)
            .show();
}

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    if (savedInstanceState != null) {
        mCurrentIndex = savedInstanceState.getInt(KEY_INDEX, 0);
    }
    super.onCreate(savedInstanceState);
    Log.d(TAG, "onCreate(Bundle) called");
    setContentView(R.layout.activity_quiz);

    mQuestionTextView = (TextView) findViewById(R.id.question_text_view);

    mTrueButton = (Button) findViewById(R.id.trueButton);
    mTrueButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            checkAnswer(true);
        }
    });

    mFalseButton = (Button) findViewById(R.id.falseButton);
    mFalseButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            checkAnswer(false);
        }
    });

    mNextButton = (ImageButton) findViewById(R.id.nextButton);
    mNextButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            mCurrentIndex = (mCurrentIndex + 1) % mQuestionBank.length;
            mIsCheater = false;
            updateQuestion();
        }
    });

    mCheatButton = (Button)findViewById(R.id.cheatButton);
    mCheatButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            boolean answerIsTrue = mQuestionBank[mCurrentIndex].isAnswerTrue();
            Intent i = CheatActivity.newIntent(QuizActivity.this, answerIsTrue);
            startActivityForResult(i, REQUEST_CODE_CHEAT);
        }
    });



    updateQuestion();
}

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putInt(KEY_INDEX, mCurrentIndex);
}

@Override
protected void onStart() {
    super.onStart();
    Log.d(TAG, "onStart() called");
}

@Override
protected void onPause() {
    super.onPause();
    Log.d(TAG, "onPause() called");
}

@Override
protected void onResume() {
    super.onResume();
    Log.d(TAG, "onResume() called");
}

@Override
protected void onStop() {
    super.onStop();
    Log.d(TAG, "onStop() called");
}

@Override
protected void onDestroy() {
    super.onDestroy();
    Log.d(TAG, "onDestroy() called");
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (resultCode != Activity.RESULT_OK) {
        return;
    }

    if (requestCode == REQUEST_CODE_CHEAT) {
        if (data == null) {
            return;
        }
        mIsCheater = CheatActivity.wasAnswerShown(data);
    }
}
   }

我的CheatActivity课程

  package com.example.ryan.ryans_quiz;

  import android.animation.Animator;
  import android.animation.AnimatorListenerAdapter;
  import android.content.Context;
  import android.content.Intent;
  import android.os.Build;
  import android.os.Bundle;
  import android.support.design.widget.FloatingActionButton;
  import android.support.design.widget.Snackbar;
  import android.support.v7.app.AppCompatActivity;
  import android.support.v7.widget.Toolbar;
  import android.view.Menu;
  import android.view.MenuItem;
  import android.view.View;
  import android.view.ViewAnimationUtils;
  import android.widget.Button;
  import android.widget.TextView;

  public class
    CheatActivity extends AppCompatActivity {
       private static final String EXTRA_ANSWER_IS_TRUE =
        "com.bignerdranch.android.geoquiz.answer_is_true";
       private static final String EXTRA_ANSWER_SHOWN =
        "com.bignerdranch.android.geoquiz.answer_shown";

   private boolean mAnswerIsTrue;

   private TextView mAnswerTextView;
   private Button mShowAnswer;

   public static Intent newIntent(Context packageContext, boolean answerIsTrue) {
    Intent i = new Intent(packageContext, CheatActivity.class);
    i.putExtra(EXTRA_ANSWER_IS_TRUE, answerIsTrue);
    return i;
}

   public static boolean wasAnswerShown(Intent result) {
    return result.getBooleanExtra(EXTRA_ANSWER_SHOWN, false);
}

   private void setAnswerShownResult(boolean isAnswerShown) {
    Intent data = new Intent();
    data.putExtra(EXTRA_ANSWER_SHOWN, isAnswerShown);
    setResult(RESULT_OK, data);
}

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

    mAnswerIsTrue = getIntent().getBooleanExtra(EXTRA_ANSWER_IS_TRUE, false);

    mAnswerTextView = (TextView)findViewById(R.id.answer_text_view);
    mShowAnswer = (Button)findViewById(R.id.show_answer_button);
    mShowAnswer.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if (mAnswerIsTrue) {
                mAnswerTextView.setText(R.string.trueButton);
            } else {
                mAnswerTextView.setText(R.string.falseButton);
            }
            setAnswerShownResult(true);

            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
                int cx = mShowAnswer.getWidth() / 2;
                int cy = mShowAnswer.getHeight() / 2;
                float radius = mShowAnswer.getWidth();
                Animator anim = ViewAnimationUtils
                        .createCircularReveal(mShowAnswer, cx, cy, radius, 0);
                anim.addListener(new AnimatorListenerAdapter() {
                    @Override
                    public void onAnimationEnd(Animator animation) {
                        super.onAnimationEnd(animation);
                        mAnswerTextView.setVisibility(View.VISIBLE);
                        mShowAnswer.setVisibility(View.INVISIBLE);
                    }
                });
                anim.start();
            } else {
                mAnswerTextView.setVisibility(View.VISIBLE);
                mShowAnswer.setVisibility(View.INVISIBLE);
            }
        }
    });

}

我的问题类

    package com.example.ryan.ryans_quiz;

    /**
             * Created by Ryan on 1/20/2016.
     */
    public class Question {
        private int mTextResId;
        private boolean mAnswerTrue;

        public Question(int _textResId, boolean _answerTrue) {
            mTextResId = _textResId;
            mAnswerTrue = _answerTrue;
                }

        public int getTextResId() {
            return mTextResId;
        }

        public void setTextResId(int textResId) {
            mTextResId = textResId;
        }

        public boolean isAnswerTrue() {
    return mAnswerTrue;
}

public void setAnswerTrue(boolean answerTrue) {
    mAnswerTrue = answerTrue;
}

    }

最后是我的xml文件......

activity_cheat 

  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
          xmlns:tools="http://schemas.android.com/tools"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_gravity="center"
          android:orientation="vertical"
          tools:context="com.example.ryan.ryans_quiz.CheatActivity">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:padding="24dp"
    android:text="@string/warning_text"/>

<TextView
    android:id="@+id/answer_text_view"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:padding="24dp"
    tools:text="Answer"/>

<Button
    android:id="@+id/show_answer_button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:text="@string/show_answer_button"/>


  </LinearLayout>

LandLayout - activity_quiz 

  <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:gravity="center"
         android:orientation="vertical">

<TextView
    android:id="@+id/question_text_view"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center_horizontal"
    android:padding="24dp"/>

<LinearLayout
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center_horizontal|center_vertical"
    android:orientation="vertical">

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal|center_vertical"
        android:orientation="horizontal">

        <Button
            android:id="@+id/trueButton"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/trueButton"/>

        <Button
            android:id="@+id/falseButton"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/falseButton"/>
    </LinearLayout>

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|center"
        android:text="@string/cheat_button"/>

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal|center_vertical"
        android:orientation="horizontal">

        <ImageButton
            android:id="@+id/previousButton"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:contentDescription="@string/previousButton"
            android:src="@drawable/arrow_left"/>

        <ImageButton
            android:id="@+id/nextButton"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_gravity="center_horizontal|center_vertical"
            android:contentDescription="@string/nextButton"
            android:src="@drawable/arrow_right"/>

    </LinearLayout>
  </LinearLayout>
 </FrameLayout>

vertical layout- activity_quiz 

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:gravity="center"
          android:orientation="vertical">

<TextView
    android:id="@+id/question_text_view"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:padding="24dp"/>

<LinearLayout
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="horizontal">

    <Button
        android:id="@+id/trueButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/trueButton"/>

    <Button
        android:id="@+id/falseButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/falseButton"/>

</LinearLayout>

<Button
    android:id="@+id/cheatButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/cheat_button"/>

<LinearLayout
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="horizontal">

    <ImageButton
        android:id="@+id/previousButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:contentDescription="@string/previousButton"
        android:src="@drawable/arrow_left"/>

    <ImageButton
        android:id="@+id/nextButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:contentDescription="@string/nextButton"
        android:src="@drawable/arrow_right"/>


  </LinearLayout>
 </LinearLayout>

的字符串.. 

  <resources>
<string name="app_name">RyanHull_Quiz</string>
<string name="action_settings">Settings</string>

<string name="trueButton">True</string>
<string name="falseButton">False</string>
<string name="nextButton">Next</string>
<string name="previousButton">Previous</string>
<string name="cheat_button">Cheat!</string>

<string name="correct_toast">Correct! :)</string>
<string name="incorrect_toast">Incorrect! :(</string>"

<string name="question_oceans">The Pacific Ocean is larger than the Atlantic Ocean.</string>
<string name="question_mideast">The Suez Canal connects the Red Sea and the Indian Ocean.</string>
<string name="question_africa">The source of the Nile River is in Egypt.</string>
<string name="question_americas">The Amazon River is the longest river in the Americas.</string>
<string name="question_asia">Lake Baikal is the world\'s oldest and deepest freshwater lake.</string>

<string name="warning_text">Are you sure you want to do this??</string>
<string name="show_answer_button">Show Answer</string>
<string name="judgment_toast">Cheating is Wrong 8/</string>
<string name="title_activity_cheat">Cheat</string>

并最终表现出来...... 

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

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
    <activity android:name=".QuizActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN"/>

            <category android:name="android.intent.category.LAUNCHER"/>
        </intent-filter>
    </activity>
    <!--
         ATTENTION: This was auto-generated to add Google Play services to your project for
         App Indexing.  See https://g.co/AppIndexing/AndroidStudio for more information.
    -->
    <meta-data
        android:name="com.google.android.gms.version"
        android:value="@integer/google_play_services_version"/>

    <activity
        android:name=".CheatActivity"
        android:label="@string/title_activity_cheat"
        android:theme="@style/AppTheme.NoActionBar">
    </activity>
</application>

编辑：我不知道异常是什么..更多关于找到地点和原因的问题......

3 个答案:

答案 0 :(得分：1)

mCheatButton的查找失败，因为您忘记在activity_quiz.xml布局文件的横向版本中为其分配ID。

然后尝试在ClickListener来自的空对象上设置NullPointerException。

答案 1 :(得分：1)

当你旋转设备时，QuizActivity会破坏然后调用onCreate，但你的LandLayout文件没有名为'cheatButton'的Button，所以findViewById（R.id.cheatButton）将返回null给mCheatButton，它不能调用任何方法

答案 2 :(得分：0)

您尚未在LandLayout - activity_quiz

中分配任何ID作弊按钮

更改

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom|center"
    android:text="@string/cheat_button"/>

到

<Button
    android:id="@+id/cheatButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom|center"
    android:text="@string/cheat_button"/>
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