Neil Ruggiero Neil Ruggiero - 18 days ago 4
Android Question

Null Pointer Exception when calling getResources()

I'm making a quiz program for android, and to keep things compatible for different languages, I've put all my quiz questions and labels in my strings.xml file. Basically the functionality I'm looking for is to have the first question display in a TextView, then when the user submits their answer, it updates to the next question.

Here is my code along with the error message I'm getting.

--------- beginning of crash
11-16 10:37:21.723 26952-26952/com.example.neil.bsgquiz E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.neil.bsgquiz, PID: 26952
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.neil.bsgquiz/com.example.neil.bsgquiz.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2337)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5443)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
at android.content.ContextWrapper.getResources(ContextWrapper.java:87)
at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:81)
at android.support.v7.app.AppCompatActivity.getResources(AppCompatActivity.java:551)
at com.example.neil.bsgquiz.MainActivity.<init>(MainActivity.java:28)
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1090)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2327)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490) 
at android.app.ActivityThread.-wrap11(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5443) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 




package com.example.neil.bsgquiz;

import android.content.res.Resources;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import org.w3c.dom.Text;

import static android.icu.lang.UCharacter.GraphemeClusterBreak.T;

public class MainActivity extends AppCompatActivity {

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

int correctAnswers = 0;
int questionCounter = 0;

//TODO Bug seems to be in this section, about getting resources.

//get question header array from resources
Resources res = getResources();
String[] questionHeaders = res.getStringArray(R.array.question_header_array);

//get answer key array from resources
String[] answerKey = res.getStringArray(R.array.answer_key_array);

//get questions from resources
String[] questions = res.getStringArray(R.array.questions_array);


public void submitAnswer() {
//create Edit Text object, and extract user input answer from it
EditText userAnswerEditText = (EditText) findViewById(R.id.answer_text);
String userAnswer = userAnswerEditText.getText().toString();

//compare against answer key and tell user if right or wrong
if (userAnswer.compareToIgnoreCase(answerKey[questionCounter]) == 0) {
Toast.makeText(this, "That's Correct!", Toast.LENGTH_SHORT).show();
correctAnswers++;
} else {
Toast.makeText(this, "Sorry, That's Incorrect", Toast.LENGTH_SHORT).show();
}
nextQuestion();
}

/**
* @param questionNumber: what question are we getting a hint for
* @return String containing a hint to give to the user
*/
private String getHint(int questionNumber) {
return "0";
}

private void nextQuestion() {
//step forward question header
TextView headerText = (TextView) findViewById(R.id.question_header);
headerText.setText(questionHeaders[questionCounter]);

//step forward question text
TextView questionText = (TextView) findViewById(R.id.question_text_view);
questionText.setText(questions[questionCounter]);

//reset hint for EditText
EditText userAnswerEditText = (EditText) findViewById(R.id.answer_text);
userAnswerEditText.setHint("Answer");

//update correct answer counter
TextView correctAnswers = (TextView) findViewById(R.id.correct_answer_counter);
correctAnswers.setText(correctAnswers + " / 8");

questionCounter++;
}
}

Answer

You're accessing resources too early, in MainActivity.<init> e.g. field initialization. You can only use your activity as a Context with Resources in onCreate() or later in the activity lifecycle.

Move the getResources() and getStringArray() calls to onCreate().

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