在我的应用中，用户可以选择3种不同类型的测验。当他们选择一种称为“级别”的测验类型时，我得到一个NullPointerException。 “等级”算法的顺序与游戏类型为“原始”时的顺序相同。您可以在下面的代码中看到这一点。很难解释为什么算法是相同的，所以我会省去你的细节，但只是接受算法现在是相同的。 ：）
为什么我的测试/游戏类型为“级别”时会出现此NPE异常，但是当测验/游戏类型为“原始”时，即使它们的代码/算法相同，也是如此？
public class QuestionView extends Activity {
int correctAnswers = 0;
int wrongAnswers = 0;
int answer = 0;
int i = 0;
long score = 0;
long startTime = 20000;
long interval = 1000;
long points;
boolean timerHasStarted = false;
String category;
Button answer1, answer2, answer3, answer4;
TextView question, pointCounter, questionNumber, timeCounter, timeremaining;
ArrayList<Question> queries;
public static ArrayList<Long> pointsPerQuestion = new ArrayList<Long>(10);
Timer cdTimer;
ProgressBar bar;
Context c;
Singleton singleton = Singleton.getInstance();
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.questionview);
c = this;
answer1 = (Button)findViewById(R.id.answer1);
answer2 = (Button)findViewById(R.id.answer2);
answer3 = (Button)findViewById(R.id.answer3);
answer4 = (Button)findViewById(R.id.answer4);
question = (TextView)findViewById(R.id.question);
questionNumber = (TextView)findViewById(R.id.questionnumber);
timeremaining = (TextView)findViewById(R.id.timeremaining);
category = getIntent().getStringExtra("category");
queries = getIntent().getParcelableArrayListExtra("queries");
pointsPerQuestion.clear();
if(singleton.getGameType() == "levels") {
if(singleton.getLevel() <= 10) {
cdTimer = new Timer(startTime, interval);
bar = (ProgressBar)findViewById(R.id.progressbar);
bar.setIndeterminate(false);
bar.setMax(20000);
loadLevelsQuizTen();
}
//...
} else if (singleton.getGameType() == "original") {
cdTimer = new Timer(startTime, interval);
bar = (ProgressBar)findViewById(R.id.progressbar);
bar.setIndeterminate(false);
bar.setMax(20000);
loadOriginalQuiz();
} else if (singleton.getGameType() == "freeplay") {
loadFreeplayQuiz();
}
}
public void loadFreeplayQuiz() {
//...
}
public void loadLevelsQuizTen() {
if(i == 10) {
cdTimer.cancel();
endQuiz();
} else {
if(!timerHasStarted) {
cdTimer.start();
timerHasStarted = true;
} else {
cdTimer.start();
timerHasStarted = false;
}
//answer = queries.get(i).getCorrectAnswer(); //NULLPOINTEREXCEPTION HERE
answer = 2;
question.setText(queries.get(i).getQuery()); // I COMMENTED OUT ABOVE LINE OF CODE AND NOW NPE IS NOW HERE
answer1.setText(queries.get(i).getA1());
answer2.setText(queries.get(i).getA2());
answer3.setText(queries.get(i).getA3());
answer4.setText(queries.get(i).getA4());
answer1.setOnClickListener(new OnClickListener() {
//...
}
});
answer2.setOnClickListener(new OnClickListener() {
//...
});
answer3.setOnClickListener(new OnClickListener() {
//...
});
answer4.setOnClickListener(new OnClickListener() {
//...
});
}
}
public void loadOriginalQuiz() {
if(i == 10) {
cdTimer.cancel();
endQuiz();
} else {
if(!timerHasStarted) {
cdTimer.start();
timerHasStarted = true;
} else {
cdTimer.start();
timerHasStarted = false;
}
answer = queries.get(i).getCorrectAnswer();
question.setText(queries.get(i).getQuery());
answer1.setText(queries.get(i).getA1());
answer2.setText(queries.get(i).getA2());
answer3.setText(queries.get(i).getA3());
answer4.setText(queries.get(i).getA4());
answer1.setOnClickListener(new OnClickListener() {
//...
});
answer2.setOnClickListener(new OnClickListener() {
//...
});
answer3.setOnClickListener(new OnClickListener() {
//...
});
answer4.setOnClickListener(new OnClickListener() {
//...
});
}
}
public ArrayList<Question> getQueries() {
return queries;
}
public static ArrayList<Long> getPointsPerQuestion() {
//...
}
public void correct() {
pointsPerQuestion.add(points);
score = score + points;
i++;
if(singleton.getGameType() == "original") {
loadOriginalQuiz();
} else if(singleton.getGameType() == "levels") {
loadLevelsQuizTen();
}
}
public void incorrect() {
long zero = 0;
pointsPerQuestion.add(zero);
i++;
loadOriginalQuiz();
}
public class Timer extends CountDownTimer {
public Timer(long startTime, long interval) {
super(startTime, interval);
}
@Override
public void onFinish() {
points = 0;
if(i >= 9) {
cdTimer.cancel();
pointsPerQuestion.add(points);
endQuiz();
} else {
wrongAnswers++;
incorrect();
}
}
@Override
public void onTick(long millisUntilFinished) {
bar.setProgress((int) millisUntilFinished);
points = (millisUntilFinished / 200) + 1;
timeremaining.setText("Score remaining: " + points);
if(i < 10) {
questionNumber.setText(c.getResources().getString(R.string.question) + " " + (i + 1) + " " + c.getResources().getString(R.string.of10));
}
}
}
public void endQuiz() {
Intent intent = new Intent(QuestionView.this, Results.class);
intent.putExtra("correctAnswers", correctAnswers);
intent.putExtra("wrongAnswers", wrongAnswers);
intent.putExtra("score", score);
intent.putExtra("pointsPerQuestion", pointsPerQuestion);
intent.putParcelableArrayListExtra("queries", queries);
intent.putExtra("category", category);
startActivity(intent);
}
public void onStop() {
super.onStop();
}
public void onResume() {
super.onResume();
}
}
logcat的
06-14 20:44:45.413: E/AndroidRuntime(1335): java.lang.RuntimeException: Unable to start activity ComponentInfo{matt.lyons.bibletrivia.lite/matt.lyons.bibletrivia.lite.QuestionView}: java.lang.NullPointerException
06-14 20:44:45.413: E/AndroidRuntime(1335): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
06-14 20:44:45.413: E/AndroidRuntime(1335): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
06-14 20:44:45.413: E/AndroidRuntime(1335): at android.app.ActivityThread.access$600(ActivityThread.java:141)
06-14 20:44:45.413: E/AndroidRuntime(1335): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
06-14 20:44:45.413: E/AndroidRuntime(1335): at android.os.Handler.dispatchMessage(Handler.java:99)
06-14 20:44:45.413: E/AndroidRuntime(1335): at android.os.Looper.loop(Looper.java:137)
06-14 20:44:45.413: E/AndroidRuntime(1335): at android.app.ActivityThread.main(ActivityThread.java:5041)
06-14 20:44:45.413: E/AndroidRuntime(1335): at java.lang.reflect.Method.invokeNative(Native Method)
06-14 20:44:45.413: E/AndroidRuntime(1335): at java.lang.reflect.Method.invoke(Method.java:511)
06-14 20:44:45.413: E/AndroidRuntime(1335): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
06-14 20:44:45.413: E/AndroidRuntime(1335): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
06-14 20:44:45.413: E/AndroidRuntime(1335): at dalvik.system.NativeStart.main(Native Method)
06-14 20:44:45.413: E/AndroidRuntime(1335): Caused by: java.lang.NullPointerException
06-14 20:44:45.413: E/AndroidRuntime(1335): at matt.lyons.bibletrivia.lite.QuestionView.loadLevelsQuizTen(QuestionView.java:195)
06-14 20:44:45.413: E/AndroidRuntime(1335): at matt.lyons.bibletrivia.lite.QuestionView.onCreate(QuestionView.java:80)
06-14 20:44:45.413: E/AndroidRuntime(1335): at android.app.Activity.performCreate(Activity.java:5104)
06-14 20:44:45.413: E/AndroidRuntime(1335): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
06-14 20:44:45.413: E/AndroidRuntime(1335): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
答案 0 :(得分：3)
为什么“接受”？这可能是你论证中的致命缺陷。
问题在于：
Caused by: java.lang.NullPointerException
06-14 20:44:45.413: E/AndroidRuntime(1335): at matt.lyons.bibletrivia.lite.QuestionView.loadLevelsQuizTen(QuestionView.java:195)
转到QuestionView.java文件中的第195行，查看该行上的对象引用，并查看哪一个未能初始化。
你越早停止告诉自己一切都很好并开始关注真正发生的事情，你就能越早解决问题并继续前进。
您不应该复制任何代码。您应该将它封装在单个方法调用中并在两个位置调用它。这是一个错误的秘诀。
你还有很多其他问题。您使用私有数据成员i以不同的方法执行不同的操作。它没有以我能看到的任何方式同步。我认为没有理由为什么这个值不能作为方法参数并传入。这将更加线程安全。
当你做这样的事情时，将字符串与==进行比较，并复制代码，它会让你所做的一切都对我产生怀疑。难怪你遇到麻烦了。投票结束。
答案 1 :(得分：2)
设置断点，获取NPE并检查变量的值。我猜想queries是空的（没有正确设置或从意图包中获取），或queries.get(i)为空。
答案 2 :(得分：0)
您收到错误，因为您正在调用两种不同的方法。在您致电loadLevelsQuizTen();的级别中，原来您致电loadOriginalQuiz();
尽管你说他们是相同的，但事实并非如此。我将使用调试器逐步完成该方法并找出什么是null以及为什么。