当我点击我的测验按钮时，任何人都可以帮助我，当在模拟器上运行时，应用会停止。我从互联网上获得了代码，但是在教程中，当应用程序打开时，测验会启动。使用我的应用程序，该人首先需要点击测验按钮，然后测验必须开始。
MainActivity：
package app.mobiledevicesecurity;
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
public class MainActivity extends ActionBarActivity {
DatabaseHelper myDb;
private static Button readbtn;
private static Button quizbtn;
private static Button scoresbtn;
private static Button settingsbtn;
private static Button helpbtn;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
myDb = new DatabaseHelper(this);
myDb.insertData();
OnClickReadButtonListener();
OnClickQuizButtonListener();
OnClickScoresButtonListener();
OnClickSettingsButtonListener();
OnClickHelpButtonListener();
}
public void OnClickReadButtonListener() {
readbtn = (Button) findViewById(R.id.readbutton);
readbtn.setOnClickListener(
new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent("app.mobiledevicesecurity.Read_Category");
startActivity(intent);
}
}
);
}
public void OnClickQuizButtonListener() {
quizbtn = (Button) findViewById(R.id.quizbutton);
quizbtn.setOnClickListener(
new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent("app.mobiledevicesecurity.Quiz");
startActivity(intent);
}
}
);
}
public void OnClickScoresButtonListener() {
scoresbtn = (Button) findViewById(R.id.scoresbutton);
scoresbtn.setOnClickListener(
new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent("app.mobiledevicesecurity.Scores");
startActivity(intent);
}
}
);
}
public void OnClickSettingsButtonListener() {
settingsbtn = (Button) findViewById(R.id.settingsbutton);
settingsbtn.setOnClickListener(
new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent("app.mobiledevicesecurity.Settings");
startActivity(intent);
}
}
);
}
public void OnClickHelpButtonListener() {
helpbtn = (Button) findViewById(R.id.helpbutton);
helpbtn.setOnClickListener(
new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent("app.mobiledevicesecurity.Help");
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_main, 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);
}
}
问题：
package app.mobiledevicesecurity;
/**
* Created by Martin on 2015/08/28.
*/
import android.app.Activity;
public class Question extends Activity {
private int ID;
private String QUESTION;
private String OPTA;
private String OPTB;
private String OPTC;
private String ANSWER;
public Question() {
ID = 0;
QUESTION = "";
OPTA = "";
OPTB = "";
OPTC = "";
ANSWER = "";
}
public Question(String qUESTION, String oPTA, String oPTB, String oPTC,
String aNSWER) {
QUESTION = qUESTION;
OPTA = oPTA;
OPTB = oPTB;
OPTC = oPTC;
ANSWER = aNSWER;
}
public int getID() {
return ID;
}
public String getQUESTION() {
return QUESTION;
}
public String getOPTA() {
return OPTA;
}
public String getOPTB() {
return OPTB;
}
public String getOPTC() {
return OPTC;
}
public String getANSWER() {
return ANSWER;
}
public void setID(int id) {
ID = id;
}
public void setQUESTION(String qUESTION) {
QUESTION = qUESTION;
}
public void setOPTA(String oPTA) {
OPTA = oPTA;
}
public void setOPTB(String oPTB) {
OPTB = oPTB;
}
public void setOPTC(String oPTC) {
OPTC = oPTC;
}
public void setANSWER(String aNSWER) {
ANSWER = aNSWER;
}
}
QuizHelper：
package app.mobiledevicesecurity;
/**
* Created by Martin on 2015/08/28.
*/
import java.util.ArrayList;
import java.util.List;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class QuizHelper extends SQLiteOpenHelper {
private static final int DATABASE_VERSION = 1;
// Database Name
private static final String DATABASE_NAME = "mathsone";
// tasks table name
private static final String TABLE_QUEST = "quest";
// tasks Table Columns names
private static final String KEY_ID = "qid";
private static final String KEY_QUES = "question";
private static final String KEY_ANSWER = "answer"; // correct option
private static final String KEY_OPTA = "opta"; // option a
private static final String KEY_OPTB = "optb"; // option b
private static final String KEY_OPTC = "optc"; // option c
private SQLiteDatabase dbase;
public QuizHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
dbase = db;
String sql = "CREATE TABLE IF NOT EXISTS " + TABLE_QUEST + " ( "
+ KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + KEY_QUES
+ " TEXT, " + KEY_ANSWER + " TEXT, " + KEY_OPTA + " TEXT, "
+ KEY_OPTB + " TEXT, " + KEY_OPTC + " TEXT)";
db.execSQL(sql);
addQuestion();
// db.close();
}
private void addQuestion() {
Question q1 = new Question("5+2 = ?", "7", "8", "6", "7");
this.addQuestion(q1);
Question q2 = new Question("2+18 = ?", "18", "19", "20", "20");
this.addQuestion(q2);
Question q3 = new Question("10-3 = ?", "6", "7", "8", "7");
this.addQuestion(q3);
Question q4 = new Question("5+7 = ?", "12", "13", "14", "12");
this.addQuestion(q4);
Question q5 = new Question("3-1 = ?", "1", "3", "2", "2");
this.addQuestion(q5);
Question q6 = new Question("0+1 = ?", "1", "0", "10", "1");
this.addQuestion(q6);
Question q7 = new Question("9-9 = ?", "0", "9", "1", "0");
this.addQuestion(q7);
Question q8 = new Question("3+6 = ?", "8", "7", "9", "9");
this.addQuestion(q8);
Question q9 = new Question("1+5 = ?", "6", "7", "5", "6");
this.addQuestion(q9);
Question q10 = new Question("7-5 = ?", "3", "2", "6", "2");
this.addQuestion(q10);
Question q11 = new Question("7-2 = ?", "7", "6", "5", "5");
this.addQuestion(q11);
Question q12 = new Question("3+5 = ?", "8", "7", "5", "8");
this.addQuestion(q12);
Question q13 = new Question("0+6 = ?", "7", "6", "5", "6");
this.addQuestion(q13);
Question q14 = new Question("12-10 = ?", "1", "2", "3", "2");
this.addQuestion(q14);
Question q15 = new Question("12+2 = ?", "14", "15", "16", "14");
this.addQuestion(q15);
Question q16 = new Question("2-1 = ?", "2", "1", "0", "1");
this.addQuestion(q16);
Question q17 = new Question("6-6 = ?", "6", "12", "0", "0");
this.addQuestion(q17);
Question q18 = new Question("5-1 = ?", "4", "3", "2", "4");
this.addQuestion(q18);
Question q19 = new Question("4+2 = ?", "6", "7", "5", "6");
this.addQuestion(q19);
Question q20 = new Question("5+1 = ?", "6", "7", "5", "6");
this.addQuestion(q20);
Question q21 = new Question("5-4 = ?", "5", "4", "1", "1");
this.addQuestion(q21);
// END
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldV, int newV) {
// Drop older table if existed
db.execSQL("DROP TABLE IF EXISTS " + TABLE_QUEST);
// Create tables again
onCreate(db);
}
// Adding new question
public void addQuestion(Question quest) {
// SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_QUES, quest.getQUESTION());
values.put(KEY_ANSWER, quest.getANSWER());
values.put(KEY_OPTA, quest.getOPTA());
values.put(KEY_OPTB, quest.getOPTB());
values.put(KEY_OPTC, quest.getOPTC());
// Inserting Row
dbase.insert(TABLE_QUEST, null, values);
}
public List<Question> getAllQuestions() {
List<Question> quesList = new ArrayList<Question>();
// Select All Query
String selectQuery = "SELECT * FROM " + TABLE_QUEST;
dbase = this.getReadableDatabase();
Cursor cursor = dbase.rawQuery(selectQuery, null);
// looping through all rows and adding to list
if (cursor.moveToFirst()) {
do {
Question quest = new Question();
quest.setID(cursor.getInt(0));
quest.setQUESTION(cursor.getString(1));
quest.setANSWER(cursor.getString(2));
quest.setOPTA(cursor.getString(3));
quest.setOPTB(cursor.getString(4));
quest.setOPTC(cursor.getString(5));
quesList.add(quest);
} while (cursor.moveToNext());
}
// return quest list
return quesList;
}
}
结果：
package app.mobiledevicesecurity;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
public class Result extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_result);
TextView textResult = (TextView) findViewById(R.id.textResult);
Bundle b = getIntent().getExtras();
int score = b.getInt("score");
textResult.setText("Your score is " + " " + score + ". Thanks for playing my game.");
}
public void playagain(View o) {
Intent intent = new Intent(this, Quiz.class);
startActivity(intent);
}
}
的AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="app.mobiledevicesecurity" >
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".Read_Category"
android:label="@string/title_activity_read__category" >
<intent-filter>
<action android:name="app.mobiledevicesecurity.Read_Category" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name=".Quiz"
android:label="@string/title_activity_quiz" >
<intent-filter>
<action android:name="app.mobiledevicesecurity.Quiz" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name=".Scores"
android:label="@string/title_activity_scores" >
<intent-filter>
<action android:name="app.mobiledevicesecurity.Scores" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name=".Settings"
android:label="@string/title_activity_settings" >
<intent-filter>
<action android:name="app.mobiledevicesecurity.Settings" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name=".Help"
android:label="@string/title_activity_help" >
<intent-filter>
<action android:name="app.mobiledevicesecurity.Help" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name=".Result"
android:label="@string/title_activity_result" >
</activity>
</application>
</manifest>
为什么app停止/ chrash任何帮助？
测验：
package app.mobiledevicesecurity;
import java.util.List;
import java.util.Timer;
import java.util.concurrent.TimeUnit;
import android.annotation.SuppressLint;
import android.annotation.TargetApi;
import android.app.Activity;
import android.content.Intent;
import android.graphics.Typeface;
import android.media.MediaPlayer;
import android.os.Build;
import android.os.Bundle;
import android.os.CountDownTimer;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class Quiz extends Activity {
List<Question> quesList;
int score = 0;
int qid = 0;
Question currentQ;
TextView txtQuestion, times, scored;
Button button1, button2, button3;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
QuizHelper db = new QuizHelper(this); // my question bank class
quesList = db.getAllQuestions(); // this will fetch all quetonall questions
currentQ = quesList.get(qid); // the current question
txtQuestion = (TextView) findViewById(R.id.txtQuestion);
// the textview in which the question will be displayed
// the three buttons,
// the idea is to set the text of three buttons with the options from question bank
button1 = (Button) findViewById(R.id.button1);
button2 = (Button) findViewById(R.id.button2);
button3 = (Button) findViewById(R.id.button3);
// the textview in which score will be displayed
scored = (TextView) findViewById(R.id.score);
// the timer
times = (TextView) findViewById(R.id.timers);
// method which will set the things up for our game
setQuestionView();
times.setText("00:02:00");
// A timer of 60 seconds to play for, with an interval of 1 second (1000 milliseconds)
CounterClass timer = new CounterClass(60000, 1000);
timer.start();
// button click listeners
button1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// passing the button text to other method
// to check whether the anser is correct or not
// same for all three buttons
getAnswer(button1.getText().toString());
}
});
button2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
getAnswer(button2.getText().toString());
}
});
button3.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
getAnswer(button3.getText().toString());
}
});
}
public void getAnswer(String AnswerString) {
if (currentQ.getANSWER().equals(AnswerString)) {
// if conditions matches increase the int (score) by 1
// and set the text of the score view
score++;
scored.setText("Score : " + score);
} else {
// if unlucky start activity and finish the game
Intent intent = new Intent(Quiz.this,
Result.class);
// passing the int value
Bundle b = new Bundle();
b.putInt("score", score); // Your score
intent.putExtras(b); // Put your score to your next
startActivity(intent);
finish();
}
if (qid < 20) {
// if questions are not over then do this
currentQ = quesList.get(qid);
setQuestionView();
} else {
// if over do this
Intent intent = new Intent(Quiz.this,
Result.class);
Bundle b = new Bundle();
b.putInt("score", score); // Your score
intent.putExtras(b); // Put your score to your next
startActivity(intent);
finish();
}
}
@TargetApi(Build.VERSION_CODES.GINGERBREAD)
@SuppressLint("NewApi")
public class CounterClass extends CountDownTimer {
public CounterClass(long millisInFuture, long countDownInterval) {
super(millisInFuture, countDownInterval);
// TODO Auto-generated constructor stub
}
@Override
public void onFinish() {
times.setText("Time is up");
}
@Override
public void onTick(long millisUntilFinished) {
// TODO Auto-generated method stub
long millis = millisUntilFinished;
String hms = String.format(
"%02d:%02d:%02d",
TimeUnit.MILLISECONDS.toHours(millis),
TimeUnit.MILLISECONDS.toMinutes(millis)
- TimeUnit.HOURS.toMinutes(TimeUnit.MILLISECONDS
.toHours(millis)),
TimeUnit.MILLISECONDS.toSeconds(millis)
- TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS
.toMinutes(millis)));
System.out.println(hms);
times.setText(hms);
}
}
private void setQuestionView() {
// the method which will put all things together
txtQuestion.setText(currentQ.getQUESTION());
button1.setText(currentQ.getOPTA());
button2.setText(currentQ.getOPTB());
button3.setText(currentQ.getOPTC());
qid++;
}
}
logcat的：
08-28 13:35:22.081 30049-30049/? I/art﹕ Not late-enabling -Xcheck:jni (already on)
08-28 13:35:22.148 30049-30056/? E/art﹕ Failed writing handshake bytes (-1 of 14): Broken pipe
08-28 13:35:22.148 30049-30056/? I/art﹕ Debugger is no longer active
08-28 13:35:22.397 30049-30066/? D/OpenGLRenderer﹕ Use EGL_SWAP_BEHAVIOR_PRESERVED: true
08-28 13:35:22.400 30049-30049/? D/﹕ HostConnection::get() New Host Connection established 0xb3eb3f90, tid 30049
08-28 13:35:22.410 30049-30061/? I/art﹕ Background partial concurrent mark sweep GC freed 383(32KB) AllocSpace objects, 0(0B) LOS objects, 33% free, 8MB/12MB, paused 2.886ms total 102.170ms
08-28 13:35:22.421 30049-30049/? D/Atlas﹕ Validating map...
08-28 13:35:22.526 30049-30066/? D/﹕ HostConnection::get() New Host Connection established 0xb3ff7270, tid 30066
08-28 13:35:22.543 30049-30066/? I/OpenGLRenderer﹕ Initialized EGL, version 1.4
08-28 13:35:22.611 30049-30066/? D/OpenGLRenderer﹕ Enabling debug mode 0
08-28 13:35:22.618 30049-30066/? W/EGL_emulation﹕ eglSurfaceAttrib not implemented
08-28 13:35:22.618 30049-30066/? W/OpenGLRenderer﹕ Failed to set EGL_SWAP_BEHAVIOR on surface 0xb3f1ab40, error=EGL_SUCCESS
08-28 13:35:23.202 30049-30049/app.mobiledevicesecurity I/Choreographer﹕ Skipped 34 frames! The application may be doing too much work on its main thread.
08-28 13:35:29.269 30049-30049/app.mobiledevicesecurity D/AndroidRuntime﹕ Shutting down VM
08-28 13:35:29.269 30049-30049/app.mobiledevicesecurity E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: app.mobiledevicesecurity, PID: 30049
java.lang.RuntimeException: Unable to start activity ComponentInfo{app.mobiledevicesecurity/app.mobiledevicesecurity.Quiz}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5257)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at app.mobiledevicesecurity.Quiz.setQuestionView(Quiz.java:135)
at app.mobiledevicesecurity.Quiz.onCreate(Quiz.java:45)
at android.app.Activity.performCreate(Activity.java:5990)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5257)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
08-28 13:35:36.669 30049-30049/app.mobiledevicesecurity I/Process﹕ Sending signal. PID: 30049 SIG: 9
答案 0 :(得分：1)
检查此行：
txtQuestion = (TextView) findViewById(R.id.txtQuestion); // Line number : 33
确保txtQuestion中有activity_main.xml TextView。
您的应用未从txtQuestion获取activity_main.xml，因此您会在以下位置获得空指针异常：
txtQuestion.setText(currentQ.getQUESTION()); // Line number : 135
答案 1 :(得分：0)
在第29行的测验活动中，您有代码
setContentView(R.layout.activity_main);
你在夸大MainActivity的XML文件，而不是它应该是为Quiz Activity设计的XML，这就是它找不到txtQuestion并给出空指针异常的原因。
答案 2 :(得分：0)
请检查测验文件行号135 txtQuestion为NULL 或检查currentQ是否为空