我正在编写一个包含 1 个问题、3 个选择和 1 个正确答案的测验应用程序。问题、选择和答案都在 QuestionLibrary 类的数组中。 QuizActivity(主要 Activity )中的其他内容现在我设置为当问题完成时，分数将被传输到另一个 java 类(menu2)中的 TextView 但是当所有问题都完成时错误:
尝试在空对象引用上调用虚方法 void android.widget.TextView.setText(java.lang.CharSequence)
显示。哪里出错了，求助
package amapps.impossiblequiz;
import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.NavigationView;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
public class QuizActivity extends AppCompatActivity {
private DrawerLayout mDrawerLayout;
private ActionBarDrawerToggle mToggle;
private Toolbar mToolbar;
private MenuItem menuItem;
private Intent in;
private QuestionLibrary mQuestionLibrary = new QuestionLibrary();
private TextView mScoreView;
private TextView mQuestionView;
private Button mButtonChoice1;
private Button mButtonChoice2;
private Button mButtonChoice3;
private String mAnswer;
private int mScore = 0;
private int mQuestionNumber = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_quiz);
//Randromize the row of the questions
QuestionLibrary q = new QuestionLibrary();
System.out.printf("Question:0 Choice:(%s, %s, %s) Answer:%s%n",
q.getChoice1(0), q.getChoice2(0), q.getChoice3(0), q.getCorrectAnswer(0));
q.shuffle();
System.out.printf("Question:0 Choice:(%s, %s, %s) Answer:%s%n",
q.getChoice1(0), q.getChoice2(0), q.getChoice3(0), q.getCorrectAnswer(0));
//End randomizer
mToolbar = (Toolbar) findViewById(R.id.nav_action);
setSupportActionBar(mToolbar);
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawerLayout);
mToggle = new ActionBarDrawerToggle(this, mDrawerLayout, R.string.open, R.string.close);
mDrawerLayout.addDrawerListener(mToggle);
mToggle.syncState();
getSupportActionBar().setDisplayHomeAsUpEnabled(true); //Able to see the Navigation Burger "Button"
NavigationView mNavigationView = (NavigationView) findViewById(R.id.nv1);
mNavigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener(){
@Override
public boolean onNavigationItemSelected(MenuItem menuItem){
switch (menuItem.getItemId()){
case(R.id.nav_stats):
Intent accountActivity = new Intent(getApplicationContext(),Menu2.class);
startActivity(accountActivity);
}
return true;
}
});
mScoreView = (TextView) findViewById(R.id.score_score);
mQuestionView = (TextView) findViewById(R.id.question);
mButtonChoice1 = (Button) findViewById(R.id.choice1);
mButtonChoice2 = (Button) findViewById(R.id.choice2);
mButtonChoice3 = (Button) findViewById(R.id.choice3);
updateQuestion();
//Start of Button Listener1
mButtonChoice1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//My logic for Button goes in here
if (mButtonChoice1.getText() == mAnswer) {
mScore = mScore + 1;
updateScore(mScore);
updateQuestion();
mQuestionLibrary.shuffle();
//This line of code is optional...
Toast.makeText(QuizActivity.this, "Correct", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(QuizActivity.this, "Wrong... Try again!", Toast.LENGTH_SHORT).show();
mScore = 0;
updateScore(mScore);
updateQuestion();
mQuestionLibrary.shuffle();
}
}
});
//End of Button Listener1
//Start of Button Listener2
mButtonChoice2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//My logic for Button goes in here
if (mButtonChoice2.getText() == mAnswer) {
mScore = mScore + 1;
updateScore(mScore);
updateQuestion();
mQuestionLibrary.shuffle();
//This line of code is optional...
Toast.makeText(QuizActivity.this, "Correct", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(QuizActivity.this, "Oh... wrong your score is 0", Toast.LENGTH_SHORT).show();
mScore = 0;
updateScore(mScore);
updateQuestion();
mQuestionLibrary.shuffle();
}
}
});
//End of Button Listener2
//Start of Button Listener3
mButtonChoice3.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//My logic for Button goes in here
if (mButtonChoice3.getText() == mAnswer) {
mScore = mScore + 1;
updateScore(mScore);
updateQuestion();
mQuestionLibrary.shuffle();
//This line of code is optional...
Toast.makeText(QuizActivity.this, "Correct", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(QuizActivity.this, "Come on, that was not so hard...", Toast.LENGTH_SHORT).show();
mScore = 0;
updateScore(mScore);
updateQuestion();
mQuestionLibrary.shuffle();
}
}
});
//End of Button Listener3
}
private void updateQuestion() {
if (mQuestionNumber < mQuestionLibrary.getLength()) {
mQuestionView.setText(mQuestionLibrary.getQuestion(mQuestionNumber));
mButtonChoice1.setText(mQuestionLibrary.getChoice1(mQuestionNumber));
mButtonChoice2.setText(mQuestionLibrary.getChoice2(mQuestionNumber));
mButtonChoice3.setText(mQuestionLibrary.getChoice3(mQuestionNumber));
mAnswer = mQuestionLibrary.getCorrectAnswer(mQuestionNumber);
mQuestionNumber++;
}
else {
Toast.makeText(QuizActivity.this, "Last Question! You are very intelligent!", Toast.LENGTH_SHORT).show();
Intent intent = new Intent(QuizActivity.this, Menu2.class);
intent.putExtra("score",mScore); //pass score to Menu2
startActivity(intent);
}
}
private void updateScore ( int point){
mScoreView.setText("" + mScore);
}
@Override //Makes that the "Burger" Item, shows the Drawer if someone clicks on the simbol
public boolean onOptionsItemSelected (MenuItem item){
if (mToggle.onOptionsItemSelected(item)) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
public class QuestionLibrary {
private final String[] [] mChoices ={
{"1993", "1986", "1967"},
{"-260", "-272,15", "279,15"},
{"a plant","The active substance of marijuana" , "a spider"},
{"6", "10","8"},
{"12","15","10"},
{"Uranus","Neptune","Saturn"},
{"HCl","NaCl","CO"},
{"John F. Kennedy", "Richard Nixon","James A. Garfield"},
{"Canada","Denmark", "Greenland is an own state?"},
{"12","20","14"},
{"10","12","14"},
{"not","never","now"},
{"Leningrad","Wolgograd","Dimitrijgrad"}
};
private final String mQuestions[] = {
"When was the European Union founded?",
"How many Grad Celsius is one Kelvin?",
"What is THC?",
"How many legs has a spider?",
"How many stars has the European flag?",
"Which is the seventh planet from the sun?",
"What is the chemical formula of salt?",
"Who said: Ich bin ein berliner?",
"To which country belongs Greenland?",
"What is the result of: 2 + 2 *5?",
"How many mountains are higher than 8000 meter/26.246 ft?",
"A famous quote is: to be, or____ to be!",
"What is the name of Stalingrad nowadays?"
};
private final String mCorrectAnswers[] = {
"1993", "-272,15", "The active substance of marijuana",
"8", "12","Uranus","NaCl","John F. Kennedy",
"Denmark","12","14","not","Wolgograd"
};
private final List<Integer> indexes = new ArrayList<>();
public QuestionLibrary() {
for (int i = 0; i < mQuestions.length; ++i)
indexes.add(i);
}
private int index(int i) {
return indexes.get(i);
}
public String getQuestion(int a) {
return mQuestions[index(a)];
}
public String getChoice1(int a) {
return mChoices[index(a)][0];
}
public String getChoice2(int a) {
return mChoices[index(a)][1];
}
public String getChoice3(int a) {
return mChoices[index(a)][2];
}
public String getCorrectAnswer(int a) {
return mCorrectAnswers[index(a)];
}
public int getLength() {
return mQuestions.length;
}
public void shuffle() {
Collections.shuffle(indexes);
}
}
package amapps.impossiblequiz;
import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.NavigationView;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.MenuItem;
import android.widget.TextView;
import static amapps.impossiblequiz.R.id.nv2;
public class Menu2 extends AppCompatActivity {
private DrawerLayout mDrawerLayout2;
private ActionBarDrawerToggle mToggle;
private Toolbar mToolbar;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_menu2);
TextView txtScore = (TextView) findViewById(R.id.score_score);
TextView txtHighScore = (TextView) findViewById(R.id.textHighScore);
Intent intent = getIntent();
int score = intent.getIntExtra("score",0);
txtScore.setText("score" +score);
mToolbar = (Toolbar)findViewById(R.id.nav_action);
setSupportActionBar(mToolbar);
mDrawerLayout2 = (DrawerLayout) findViewById(R.id.drawerLayout2);
mToggle = new ActionBarDrawerToggle(this, mDrawerLayout2, R.string.open, R.string.close);
mDrawerLayout2.addDrawerListener(mToggle);
mToggle.syncState();
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
NavigationView mNavigationView = (NavigationView) findViewById(nv2);
mNavigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener(){
@Override
public boolean onNavigationItemSelected(MenuItem menuItem){
switch (menuItem.getItemId()){
case(R.id.nav_home2):
Intent accountActivity2 = new Intent(getApplicationContext(),QuizActivity.class);
startActivity(accountActivity2);
}
return true;
}
});
}
@Override //Makes that the "Burger" Item, shows the Drawer if someone clicks on the simbol
public boolean onOptionsItemSelected(MenuItem item) {
if (mToggle.onOptionsItemSelected(item)) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" tools:context="amapps.impossiblequiz.QuizActivity"
android:orientation="vertical" android:weightSum="1" android:id="@+id/drawerLayout">
<RelativeLayout android:layout_width="match_parent"
android:layout_height="wrap_content">
<include layout="@layout/navigation_action"
android:layout_height="wrap_content" android:layout_width="match_parent" />
<TextView android:layout_width="match_parent"
android:layout_height="wrap_content" android:text="SCORE" android:id="@+id/score_text"
android:textSize="20sp" android:textColor="#000"
android:layout_marginTop="70dp" android:layout_alignParentTop="true"
android:layout_toRightOf="@+id/imageView2" android:layout_toEndOf="@+id/imageView2"
android:layout_marginLeft="11dp" android:layout_marginStart="11dp" />
<TextView android:layout_width="wrap_content"
android:layout_height="wrap_content" android:text="0" android:id="@+id/score_score"
android:textSize="20sp" android:textColor="#000"
android:layout_marginRight="20dp" android:layout_marginTop="20dp"
android:layout_alignBaseline="@+id/score_text"
android:layout_alignBottom="@+id/score_text"
android:layout_alignParentRight="true" android:layout_alignParentEnd="true" />
<TextView android:layout_width="match_parent"
android:layout_height="70dp" android:text="When was the European Union founded?"
android:textSize="20sp" android:padding="8dp" android:id="@+id/question"
android:textAlignment="center" android:textColor="#000"
android:layout_below="@+id/score_text"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" android:layout_marginTop="19dp" />
<Button android:layout_width="match_parent"
android:layout_height="wrap_content" android:text="1993"
android:background="#f60" android:textColor="#ffffff"
android:padding="8dp" android:id="@+id/choice1" android:textSize="17dp"
android:layout_below="@+id/question" android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" android:layout_marginTop="39dp"
android:layout_marginBottom="8dp" />
<Button android:layout_width="match_parent"
android:layout_height="wrap_content" android:text="1986"
android:background="#f60" android:textColor="#ffffff"
android:padding="8dp" android:id="@+id/choice2" android:textSize="17dp"
android:layout_below="@+id/choice1" android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" android:layout_marginTop="11dp" />
<Button android:layout_width="match_parent"
android:layout_height="wrap_content" android:text="1967"
android:background="#f60" android:textColor="#ffffff"
android:padding="8dp" android:id="@+id/choice3" android:textSize="17dp"
android:layout_marginTop="21dp" android:layout_below="@+id/choice2"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
<Button android:layout_width="match_parent"
android:layout_height="wrap_content" android:text="quit"
android:background="#B71c1c" android:textColor="#fff"
android:padding="8dp" android:id="@+id/quit" android:textSize="17dp"
android:layout_marginTop="19dp" android:layout_below="@+id/choice3"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
<ImageView android:id="@+id/imageView2"
android:layout_width="wrap_content" android:layout_height="wrap_content"
app:srcCompat="@android:drawable/star_on" android:layout_marginLeft="11dp"
android:layout_marginStart="11dp" android:layout_alignBottom="@+id/score_text"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
</RelativeLayout>
<android.support.design.widget.NavigationView
android:layout_width="wrap_content" android:layout_height="match_parent"
app:menu="@menu/navigation_menu" android:layout_gravity="start"
android:id="@+id/nv1" app:headerLayout="@layout/navigation_header"
app:itemIconTint="@drawable/tint_color_selector">
</android.support.design.widget.NavigationView>
</android.support.v4.widget.DrawerLayout>
<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" tools:context="amapps.impossiblequiz.Menu2"
android:id="@+id/drawerLayout2">
<LinearLayout android:layout_width="match_parent"
android:layout_height="match_parent" android:orientation="vertical">
<include layout="@layout/navigation_action"
android:layout_width="match_parent" android:layout_height="wrap_content" />
<TextView android:id="@+id/textScore" android:layout_width="match_parent"
android:layout_height="wrap_content" android:text="Your score:"
android:paddingBottom="20dp" android:textAppearance="@style/TextAppearance.AppCompat.Display1" />
<TextView android:id="@+id/textHighScore"
android:layout_width="match_parent" android:layout_height="wrap_content"
android:text="Highest score:" android:paddingBottom="20dp"
android:textAppearance="@style/TextAppearance.AppCompat.Display1" />
<Button android:id="@+id/button" android:layout_width="match_parent"
android:layout_height="wrap_content" android:text="Button"
android:textAppearance="@style/TextAppearance.AppCompat.Display1" />
</LinearLayout>
<android.support.design.widget.NavigationView
android:layout_width="wrap_content" android:layout_height="match_parent"
app:menu="@menu/navigation_menu2" android:layout_gravity="start"
android:id="@+id/nv2" app:headerLayout="@layout/navigation_header"
app:itemIconTint="@drawable/tint_color_selector2">
</android.support.design.widget.NavigationView>
</android.support.v4.widget.DrawerLayout>
最佳答案
你必须在从 intent 获取数据之前添加额外的内容。尝试将代码放在下面。
Intent accountActivity = new Intent(getApplicationContext(),Menu2.class);
accountActivity.putExtra("Score",somethingintscore)
startActivity(accountActivity);
使用下面的代码获得额外的。
Bundle bundle = getIntent().getExtras();
if (bundle!=null && bundle.getInt("Score") > 0){
score = bundle.getInt("Score");
txtScore.setText("score" +score);
}else
txtScore.setText("score" + 0);
关于java - 在共享首选项上打开第二个 Activity/错误时出错，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/45131807/