应用程序在旋转时崩溃，NullPointerException

Question

这里是代码。不确定是否需要更多信息。该应用程序完全按照预期和期望工作，除了屏幕旋转。当屏幕旋转时，会发生这种崩溃。我是 Android 新手，正在努力学习，如果还有其他需要，请告诉我。

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Log.d(TAG, "onCreate(Bundle) called");
    setContentView(R.layout.activity_quiz);

    if(savedInstanceState != null){
        mCurrentIndex = savedInstanceState.getInt(KEY_INDEX, 0);
    }

    mCheatButton = (Button)findViewById(R.id.cheat_button);
    mCheatButton.setOnClickListener(new View.OnClickListener() {//this is line 127

        @Override
        public void onClick(View v) {
            Intent i = new Intent(QuizActivity.this, CheatActivity.class);
            boolean answerIsTrue = mQuestionBank[mCurrentIndex].isTrueQuestion();
            i.putExtra(CheatActivity.EXTRA_ANSWER_IS_TRUE, answerIsTrue);
            startActivityForResult(i, 0);
        }
    });

这里是日志：

03-18 06:54:35.203: E/AndroidRuntime(5411): FATAL EXCEPTION: main
03-18 06:54:35.203: E/AndroidRuntime(5411): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.geoquiz/com.example.geoquiz.QuizActivity}: java.lang.NullPointerException
03-18 06:54:35.203: E/AndroidRuntime(5411):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
03-18 06:54:35.203: E/AndroidRuntime(5411):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
03-18 06:54:35.203: E/AndroidRuntime(5411):     at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3692)
03-18 06:54:35.203: E/AndroidRuntime(5411):     at android.app.ActivityThread.access$700(ActivityThread.java:141)
03-18 06:54:35.203: E/AndroidRuntime(5411):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1240)
03-18 06:54:35.203: E/AndroidRuntime(5411):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-18 06:54:35.203: E/AndroidRuntime(5411):     at android.os.Looper.loop(Looper.java:137)
03-18 06:54:35.203: E/AndroidRuntime(5411):     at android.app.ActivityThread.main(ActivityThread.java:5041)
03-18 06:54:35.203: E/AndroidRuntime(5411):     at java.lang.reflect.Method.invokeNative(Native Method)
03-18 06:54:35.203: E/AndroidRuntime(5411):     at java.lang.reflect.Method.invoke(Method.java:511)
03-18 06:54:35.203: E/AndroidRuntime(5411):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
03-18 06:54:35.203: E/AndroidRuntime(5411):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
03-18 06:54:35.203: E/AndroidRuntime(5411):     at dalvik.system.NativeStart.main(Native Method)
03-18 06:54:35.203: E/AndroidRuntime(5411): Caused by: java.lang.NullPointerException
03-18 06:54:35.203: E/AndroidRuntime(5411):     at com.example.geoquiz.QuizActivity.onCreate(QuizActivity.java:127)
03-18 06:54:35.203: E/AndroidRuntime(5411):     at android.app.Activity.performCreate(Activity.java:5104)
03-18 06:54:35.203: E/AndroidRuntime(5411):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
03-18 06:54:35.203: E/AndroidRuntime(5411):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
03-18 06:54:35.203: E/AndroidRuntime(5411):     ... 12 more

Answer 1

我猜你有横向和纵向的替代布局。并且其中一个布局没有 ID 为 cheat_button 的按钮。

如果你说 NPE 是 @mCheatButton.setOnClickListener(new View.OnClickListener() 那么 mCheatButton 我们为空。

确保布局有一个 ID 为 cheat_button 的按钮