我正在为Android制作测验程序，为了保持与不同语言的兼容性，我已将所有测验问题和标签放在我的strings.xml文件中。基本上我正在寻找的功能是在TextView中显示第一个问题，然后当用户提交他们的答案时，它会更新到下一个问题。
这是我的代码以及我收到的错误消息。
--------- 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++;
}
}
答案 0 :(得分：10)
您在MainActivity.<init>内过早访问资源，例如字段初始化。您只能在活动生命周期的Context或更高版本中将Resources onCreate()与getResources()一起使用。
将getStringArray()和onCreate()来电移至import Cocoa
import IOBluetooth
import PlaygroundSupport
class BlueDelegate : IOBluetoothDeviceInquiryDelegate {
func deviceInquiryComplete(_ sender: IOBluetoothDeviceInquiry, error: IOReturn, aborted: Bool) {
aborted
print("called")
let devices = sender.foundDevices()
for device : Any? in devices! {
if let thingy = device as? IOBluetoothDevice {
thingy.getAddress()
}
}
}
}
var delegate = BlueDelegate()
var inquiry = IOBluetoothDeviceInquiry(delegate: delegate)
inquiry?.start()
PlaygroundPage.current.needsIndefiniteExecution = true
。
答案 1 :(得分：0)
对于那些感兴趣的人，我得到了我的代码并运行了以下内容。
public class MainActivity extends AppCompatActivity {
String[] questionHeaders, answerKey, questions;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Resources res = getResources();
questionHeaders = res.getStringArray(R.array.question_header_array);
answerKey = res.getStringArray(R.array.answer_key_array);
questions = res.getStringArray(R.array.questions_array);
}
int correctAnswers = 0;
int questionCounter = 0;
onCreate()之前的主要活动中声明了三个String []数组。res内的onCreate()对象。getStringArray上调用res以加载每个String []数组答案 2 :(得分：0)
原来我的问题是我用空的Context实例化了小部件（CardView）。初始化上下文对象可以解决该问题。例如，这是我现在的工作代码，但是当我得到相同的NullPointerException时，m_context为null。
CardView m_cardView = new CardView(m_context);