尝试调用虚拟方法＆＃x27; void android.widget.textview.settext（java.lang.charsequence）＆＃x27;使用topicname.setText（getTopicName）;

Question

它在这条线上显示了一个错误，但我不知道该怎么办，请解释和帮助

向我展示我不nullpoiteRexception我不知道如何解决它，这是这种零用的null poiterexception topicname.setText（getTopicName）;

主要活动代码：

公共类主动性扩展了AppCompatactivity {

// total quiz time in minutes
private int totalTimeInMins = 1;

// Timer class object for countdown timer
private Timer quizTimer;
private int seconds = 0; // current countdown seconds

// questions array list
private List<QuestionsList> questionsLists;

// Current questions index position from  questionsLists ArrayList.
private int currentQuestionPosition = 0;

// Options
private AppCompatButton option1, option2, option3, option4;

// next button
private AppCompatButton nextBtn;

// Total questions and main question TextView
private TextView question;
private TextView questions;

// selectedOption's Value. if user not selected any option yet then it is empty by default
private String selectedOptionByUser = "";

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

    // initialize widgets from activity_main.xml file
    final ImageView backBtn = findViewById(R.id.backBtn);
    final TextView topicName = findViewById(R.id.topicName);
    final TextView timer = findViewById(R.id.timer);
    question = findViewById(R.id.question);
    questions = findViewById(R.id.questions);
    option1 = findViewById(R.id.option1);
    option2 = findViewById(R.id.option2);
    option3 = findViewById(R.id.option3);
    option4 = findViewById(R.id.option4);
    nextBtn = findViewById(R.id.nextButton);

    // get Topic Name and User Name from StartActivity via Intent
    final String getTopicName = getIntent().getStringExtra("selectedTopic");

    // set Topic Name to TextView
    topicName.setText(getTopicName);

    // start quiz countdown timer
    startTimer(timer);

    // get questions from QuestionsBank class according to selectedTopicName and assign to questionsLists ArrayList
    questionsLists = QuestionsBank.getQuestions(getTopicName);

它说“ 67”行有问题，但是IDK是什么...

这是一个：topicname.setText（getTopicName）;

错误messgae说：

引起： 在com.learnoset.offlinequizapp.mainactivity.oncreate（MainActivity.java:67）