java - Android 应用程序因 NPE 崩溃

Question

我使用 Android Studio 制作了一个问答应用程序，但它总是崩溃。侧面没有显示任何错误(它标记为绿色)，但在我第一次尝试提交答案后它崩溃了。我发现在onClick方法中抛出了空指针异常。我已经查看并尝试了我能找到的解决方案，但到目前为止无法修复此错误。以下是崩溃页面的代码。任何帮助将不胜感激。

    package com.example.jeff.mygame;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.TextView;


public class QuestionActivity extends Activity {
    Intent intent;
    TextView tv;
    Button submitButton;
    RadioGroup radioGroup;
    RadioButton choice1, choice2, choice3, givenAnswer;
    String answersText;
    String questions[] = {"Which studio developed Elder Scrolls V: Skyrim?", "Who is the main character in the Mass Effect series?",
            "Which indie games company developed the Walking Dead series?"};
    String answers[] = {"Bethesda", "Commander Shepard", "TellTale Games"};
    String choices[] = {"Bioware", "Bethesda", "Ubisoft", "Commander Shepard", "Garrus Vakarian", "Illusive Man", "Team Meat", "Way Forward", "TellTale Games"};
    int flag = 0;
    public static int results, correct, incorrect;

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

        tv = (TextView)findViewById(R.id.tvQ1);
        choice1 = (RadioButton)findViewById(R.id.rb1);
        choice2 = (RadioButton)findViewById(R.id.rb2);
        choice3 = (RadioButton)findViewById(R.id.rb3);
        submitButton = (Button)findViewById(R.id.submit1);

        tv.setText(questions[flag]);
        choice1.setText(choices[0]);
        choice2.setText(choices[1]);
        choice3.setText(choices[2]);
        submitButton.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                givenAnswer = (RadioButton)findViewById(radioGroup.getCheckedRadioButtonId());
                answersText = givenAnswer.getText().toString();

                if(answersText.equals(answers[flag])){
                    correct++;
                }else{
                    incorrect++;
                }flag++;
                if(flag < questions.length){
                    tv.setText(questions[flag]);
                    choice1.setText(choices[flag*3]);
                    choice2.setText(choices[flag*3]);
                    choice3.setText(choices[flag*3]);
                }else{
                    results = correct;
                    intent = new Intent(getApplicationContext(),FinishActivity.class);
                    startActivity(intent);
                }
            }
        });
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_question, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

这是我一开始忘记添加的 logcat。

05-05 17:34:49.744      652-658/com.example.jeff.mygame I/dalvikvm﹕ threadid=3: reacting to signal 3
05-05 17:34:49.775      652-658/com.example.jeff.mygame I/dalvikvm﹕ Wrote stack traces to '/data/anr/traces.txt'
05-05 17:34:51.595      652-652/com.example.jeff.mygame I/Process﹕ Sending signal. PID: 652 SIG: 9
05-05 17:42:07.295      704-709/com.example.jeff.mygame I/dalvikvm﹕ threadid=3: reacting to signal 3
05-05 17:42:07.465      704-709/com.example.jeff.mygame I/dalvikvm﹕ Wrote stack traces to '/data/anr/traces.txt'
05-05 17:42:07.775      704-709/com.example.jeff.mygame I/dalvikvm﹕ threadid=3: reacting to signal 3
05-05 17:42:07.885      704-709/com.example.jeff.mygame I/dalvikvm﹕ Wrote stack traces to '/data/anr/traces.txt'
05-05 17:42:08.105      704-704/com.example.jeff.mygame D/gralloc_goldfish﹕ Emulator without GPU emulation detected.
05-05 17:42:11.465      704-704/com.example.jeff.mygame D/AndroidRuntime﹕ Shutting down VM
05-05 17:42:11.465      704-704/com.example.jeff.mygame W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x409c01f8)
05-05 17:42:11.475      704-704/com.example.jeff.mygame E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.NullPointerException
            at com.example.jeff.mygame.QuestionActivity$1.onClick(QuestionActivity.java:48)
            at android.view.View.performClick(View.java:3511)
            at android.view.View$PerformClick.run(View.java:14105)
            at android.os.Handler.handleCallback(Handler.java:605)
            at android.os.Handler.dispatchMessage(Handler.java:92)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4424)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
            at dalvik.system.NativeStart.main(Native Method)
05-05 17:42:12.015      704-709/com.example.jeff.mygame I/dalvikvm﹕ threadid=3: reacting to signal 3
05-05 17:42:12.025      704-709/com.example.jeff.mygame I/dalvikvm﹕ Wrote stack traces to '/data/anr/traces.txt'
05-05 17:42:15.525      704-704/com.example.jeff.mygame I/Process﹕ Sending signal. PID: 704 SIG: 9

Answer 1

您尚未初始化radioGroup。您需要执行以下操作

radioGroup = (RadioGroup) findViewById(R.id.myRadioGroup);  
radioGroup.setOnCheckedChangeListener(new OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(RadioGroup group, int checkedId) {
                        // find which radio button is selected
                        if(checkedId == R.id.rb1) {
                        // do action
                       }
           }
});
button.setOnClickListener(new OnClickListener() { 
         @Override          
         public void onClick(View v) {
                        int selectedId = radioGroup.getCheckedRadioButtonId();
                        // find which radioButton is checked by id
                        if(selectedId == R.id.rb1 ) { 
                          // you have chosen so and so radio button
                        } 
                         // similarly check other buttons
         } 
});