Question

每当我在模拟器中打开活动Testme时，都会遇到RuntimeException。 logcat发布在下面：

FATAL EXCEPTION: main
Process: com.learn.earn.earnlearnapp, PID: 6622
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.learn.earn.earnlearnapp/com.learn.earn.earnlearnapp.Testme}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2679)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference

代码似乎没有任何问题。我花了好几个小时试图解决这个问题。如果你能帮助我解决这个问题，那就太棒了。我的活动代码的一部分附在下面：

    public class Testme extends AppCompatActivity {

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

    }
    int qnum = 0;
    private List<TopicQuestion> questionsList = new ArrayList<>();
    private TextView txtquestion = findViewById(R.id.txtquestion);
    private Button answer1 = findViewById(R.id.btnans1);
    private Button answer2 = findViewById(R.id.btnans2);
    private Button answer3 = findViewById(R.id.btnans3);
    private Button answer4 = findViewById(R.id.btnans4);
    private boolean correct = false;



    private void readQuestions() {
        InputStream is = getResources().openRawResource(R.raw.questions);
        BufferedReader reader = new BufferedReader(
                new InputStreamReader(is, Charset.forName("UTF-8"))
        );

        String line = "";
        try {
        while (
                (line = reader.readLine()) != null) {
            //Split the data
            String[] tokens = line.split(",");
            //Read the data
            TopicQuestion question = new TopicQuestion();
            question.setTopic(tokens[0]);
            question.setQuestion(tokens[1]);
            question.setAns1(tokens[2]);
            question.setAns2(tokens[3]);
            question.setAns3(tokens[4]);
            question.setAns4(tokens[5]);
            questionsList.add(question);
        }

    }   catch (IOException e) {
            Log.wtf("MyActivity","Error reading question file on line" + line, e);
                e.printStackTrace();
            }
            {

            }
            txtquestion.setText(questionsList.get(qnum).getQuestion());
            answer1.setText(questionsList.get(qnum).getAns1());
            answer2.setText(questionsList.get(qnum).getAns3());
            answer3.setText(questionsList.get(qnum).getAns2());
            answer4.setText(questionsList.get(qnum).getAns4());

        answer1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                correct = (questionsList.get(qnum).getAns1()).equals(answer1.getText().toString());
            }
        });
        answer2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                correct = (questionsList.get(qnum).getAns2()).equals(answer2.getText().toString());
            }
        });
        answer3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                correct = (questionsList.get(qnum).getAns1()).equals(answer3.getText().toString());
            }
        });
        answer4.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                correct = (questionsList.get(qnum).getAns1()).equals(answer4.getText().toString());
            }
        });
        if (correct)
        {
            qnum +=1;
            txtquestion.setText(questionsList.get(qnum).getQuestion());
            answer1.setText(questionsList.get(qnum).getAns1());
            answer2.setText(questionsList.get(qnum).getAns3());
            answer3.setText(questionsList.get(qnum).getAns2());
            answer4.setText(questionsList.get(qnum).getAns4());
        }
        else
        {
            txtquestion.setText(questionsList.get(qnum).getQuestion());
            answer1.setText(questionsList.get(qnum).getAns1());
            answer2.setText(questionsList.get(qnum).getAns3());
            answer3.setText(questionsList.get(qnum).getAns2());
            answer4.setText(questionsList.get(qnum).getAns4());
        }
    }

    }

Answer 1

您必须在OnCreate之后的setContentView中分配视图的值。

声明外面的字段：

private TextView ;
private Button; etc..

将以下行放在OnCreate

中

 txtquestion = findViewById(R.id.txtquestion);
 answer1 = findViewById(R.id.btnans1);
 answer2 = findViewById(R.id.btnans2);
 answer3 = findViewById(R.id.btnans3);
 answer4 = findViewById(R.id.btnans4);

希望它有所帮助！

错误我无法解决：尝试在空对象引用上调用虚方法'android.view.Window $ Callback android.view.Window.getCallback（）'

1 个答案: