爲什麼我的Android Quiz應用程序在提交答案時崩潰並且不打印問題？

Question

我的問題是雙桶，我正在開發一個簡單的測驗應用程序使用android studio。對我來說，代碼看起來不錯，編譯應用程序時沒有顯示錯誤消息。但是，當我運行應用程序時，問題（字符串）不會顯示在UI中，當我點擊提交答案按鈕時，應用程序就會崩潰。以下是我正在實施的代碼示例。任何幫助或建議將不勝感激。謝謝

package com.example.shaun.quiz; 

import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.TextView; 

public class MainActivity extends AppCompatActivity { 
    public int currentQuestion; 
    public String[] questions; 
    public String[] answers; 

    Button answerButton; 
    Button questionButton; 
    public TextView questionView; 
    public TextView answerView; 
    public EditText answerText; 

    public void main() { 
     questions = new String[]{"1+2= ?", "1+1= ?",};  /*Array of Hard Coded Questions*/ 
     answers = new String[]{"3", "2",};     /*Array of Hard Coded Answers to indexed to match the questions*/ 
     currentQuestion = -1;        /*This will index the questions to be used*/ 
     answerButton = (Button) findViewById(R.id.AnswerButton); 
     questionButton = (Button) findViewById(R.id.QuestionButton); 
     questionView = (TextView) findViewById(R.id.QuestionTextView); 
     answerView = (TextView) findViewById(R.id.AnswerTextView); 
     answerText = (EditText) findViewById(R.id.AnswerText); 

     answerButton.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       checkAnswer(); 
      } 
     }); 

     questionButton.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       showQuestion(); 
      } 
     }); 
    } 

    public void showQuestion() { 
     currentQuestion++; 
     if (currentQuestion == questions.length) 
      currentQuestion = 0; 
     questionView.setText(questions[currentQuestion]); 
     questionView.setText(""); 
     answerText.setText(""); 
    } 

    public boolean isCorrect(String answer) 
    { 
     return (answer.equalsIgnoreCase(answers[currentQuestion])); 
    } 


    public void checkAnswer() 

    { 
     String answer = answerText.getText().toString(); 
     if(isCorrect(answer)) 
      answerView.setText("Correct!");            /*answerView, text view set to print the string in the event of the correct answer*/ 
     else 
      answerView.setText("Sorry, the Correct answer is "+answers[currentQuestion]); /*answers[currentQuestion] answers reads the answer to the current question in use */ 
    } 

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

Answer 1

您從不調用方法showQuestion()（除非來自按鈕），因此在創建活動時索引currentQuestion仍爲-1。

因此，當您檢查答案時，您正試圖訪問answers[-1]，導致ArrayIndexOutOfBoundsException。您應該在main()末尾呼叫showQuestion()以顯示第一個問題並將currentQuestion增加到數組的範圍內。

PS：你應該刪除questionView.setText("");showQuestion()來顯示文本。

Answer 2

您正在清除showQuestion（）方法中的questionView textview。這就是爲什麼不顯示問題的原因。

由於問題沒有在其中顯示，並且每當您嘗試選擇答案時，它只會放一個nullPointerException，因爲與答案相關的問題根本不存在。