我一直在第99行和第77行得到一个空指针异常,这是我试图打印随机类创建的随机值的地方(第99行),也是我调用setQuestion方法的地方(layout_game xml文件的第77.randomNum行)。
package com.grantsolutions.mathgamechapter1;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
import java.util.Random;
public class GameActivity extends Activity implements OnClickListener {
int correctAnswer;
Button buttonObjectChoice1;
Button buttonObjectChoice2;
Button buttonObjectChoice3;
TextView textObjectPartA //it says that textObjectPartA and B are never used;
TextView textObjectPartB;
TextView textObjectScore;
TextView textObjectLevel;
int currentScore;
int currentLevel = 1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.layout_game);
//declaring variables for game
//no longer being declared
/*int partA = 2;
int partB = 2;
correctAnswer = partA * partB;
int wrongAnswer1 = correctAnswer - 1;
int wrongAnswer2 = correctAnswer + 1;
/*this is where we link the variables
from the java code to the button UI in
activity_game xml itself
*/
TextView textObjectPartA = (TextView) findViewById(R.id.holdTextA);
TextView textObjectPartB = (TextView) findViewById(R.id.holdTextB);
textObjectScore = (TextView) findViewById(R.id.textLevel);
textObjectLevel = (TextView) findViewById(R.id.textScore);
buttonObjectChoice1 =
(Button) findViewById(R.id.choice1);
buttonObjectChoice2 =
(Button) findViewById(R.id.choice2);
buttonObjectChoice3 =
(Button) findViewById(R.id.choice3);
/*Use the setText method of the class on our objects
to show our variable values on the UI elements.
Similar to outputting to the console in the exercise,
only using the setText method*/
//telling the console to listen for button clicks from the user
buttonObjectChoice1.setOnClickListener(this);
buttonObjectChoice2.setOnClickListener(this);
buttonObjectChoice3.setOnClickListener(this);
setQuestion();
}
void setQuestion() {
Random randomNum;
randomNum = new Random();
int partA = 0;
int numberRange = currentLevel * 3;
partA = randomNum.nextInt(numberRange) + 1;
//removes possibility of a zero value
int partB = randomNum.nextInt(numberRange) + 1;
correctAnswer = partA * partB;
Log.i("info", ""+partA);
Log.i("info", ""+partB);
Log.d("info", ""+partA);
int wrongAnswer1 = correctAnswer - 2;
int wrongAnswer2 = correctAnswer + 2;
Log.i("info", ""+partA);
Log.i("info", ""+partB);
textObjectPartA.setText(""+partA); //error here
textObjectPartB.setText(""+partB);
//case for setting multiple choice buttons
int buttonLayout = randomNum.nextInt(3);
switch (buttonLayout) {
case 0:
buttonObjectChoice1.setText("" + correctAnswer);
buttonObjectChoice2.setText("" + wrongAnswer1);
buttonObjectChoice3.setText("" + wrongAnswer2);
break;
case 1:
buttonObjectChoice2.setText("" + correctAnswer);
buttonObjectChoice1.setText("" + wrongAnswer1);
buttonObjectChoice3.setText("" + wrongAnswer2);
break;
case 2:
buttonObjectChoice3.setText("" + correctAnswer);
buttonObjectChoice1.setText("" + wrongAnswer1);
buttonObjectChoice2.setText("" + wrongAnswer2);
break;
}
}
void updateScoreAndLevel(int answerGiven) {
if (isCorrect(answerGiven)) {
for (int i = 1; i <= currentLevel; i++) {
currentScore = currentScore + i;
}
} else {
currentLevel = 1;
currentScore = 0;
}
currentLevel++;
}
boolean isCorrect(int answerGiven) {
boolean correctTrueOrFalse = true;
if (answerGiven == correctAnswer) {//YAY!
Toast.makeText(getApplicationContext(), "Well Done", Toast.LENGTH_LONG).show();
}
else {//If wrong print this instead
Toast.makeText(getApplicationContext(), "You're wrong", Toast.LENGTH_SHORT).show();
} //case for each button being made
correctTrueOrFalse = false;
return correctTrueOrFalse;
}
@Override
public void onClick (View view){
//declaring a new int to use in all cases
int answerGiven;
switch (view.getId()) {
//case for each button being made
case R.id.choice1:
//button1 information goes here
//initialize a new integer with the value
//contained in buttonObjectChoice1
answerGiven = Integer.parseInt("" + buttonObjectChoice1.getText());
//check if the right answer
break;
case R.id.choice2:
//button2 information goes here
answerGiven = Integer.parseInt("" + buttonObjectChoice2.getText());
break;
case R.id.choice3:
//button 3 information goes here
answerGiven = Integer.parseInt("" + buttonObjectChoice3.getText());
break;
}
}
}
此处第99和77行的代码段
第77行
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.layout_game);
TextView textObjectPartA = (TextView) findViewById(R.id.holdTextA);
TextView textObjectPartB = (TextView) findViewById(R.id.holdTextB);
textObjectScore = (TextView) findViewById(R.id.textLevel);
textObjectLevel = (TextView) findViewById(R.id.textScore);
buttonObjectChoice1 =
(Button) findViewById(R.id.choice1);
buttonObjectChoice2 =
(Button) findViewById(R.id.choice2);
buttonObjectChoice3 =
(Button) findViewById(R.id.choice3);
/*Use the setText method of the class on our objects
to show our variable values on the UI elements.
Similar to outputting to the console in the exercise,
only using the setText method*/
//telling the console to listen for button clicks from the user
buttonObjectChoice1.setOnClickListener(this);
buttonObjectChoice2.setOnClickListener(this);
buttonObjectChoice3.setOnClickListener(this);
setQuestion(); //code error shown in this line
}
第99行
Log.i("info", ""+partA);
Log.i("info", ""+partB);
textObjectPartA.setText(""+partA); //error here
textObjectPartB.setText(""+partB);
layout_game文件
<?xml version="1.0" encoding="utf-8"?>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="2"
android:id="@+id/holdTextA"
android:layout_marginTop="44dp"
android:textSize="50sp"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginLeft="44dp"
android:layout_marginStart="44dp" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="X"
android:id="@+id/textView4"
android:layout_alignTop="@+id/holdTextA"
android:layout_centerHorizontal="true"
android:textSize="50sp" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="4"
android:id="@+id/holdTextB"
android:textSize="50sp"
android:layout_above="@+id/textView6"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:layout_marginRight="53dp"
android:layout_marginEnd="53dp" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="="
android:id="@+id/textView6"
android:layout_marginTop="118dp"
android:layout_below="@+id/textView4"
android:layout_alignLeft="@+id/textView4"
android:layout_alignStart="@+id/textView4"
android:textSize="60sp" />
<Button
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/choice1"
android:text="2"
android:textSize="40sp"
android:layout_alignParentBottom="true"
android:layout_alignRight="@+id/holdTextA"
android:layout_alignEnd="@+id/holdTextA"
android:layout_marginBottom="37dp" />
<Button
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="4"
android:id="@+id/choice2"
android:layout_alignBottom="@+id/choice1"
android:layout_alignLeft="@+id/holdTextB"
android:layout_alignStart="@+id/holdTextB"
android:textSize="40sp" />
<Button
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="3"
android:id="@+id/choice3"
android:layout_alignBottom="@+id/choice1"
android:layout_centerHorizontal="true"
android:layout_alignTop="@+id/choice1"
android:textSize="40sp" />
