Question

我是Android开发的新手，我正在尝试为学校项目构建应用程序。我搜索了互联网，找到了我想要创建的Math应用程序的一些指南/代码。我复制/粘贴其中一些，我设法创建了更好的用户界面。当我启动游戏时一切都很好，但是当我玩游戏时崩溃了。游戏是关于基本的数学运算。答案是随机的（例如5x5 =？），用户必须回答。如果答案是正确的，则会出现一个勾号，当出现错误时，会出现十字。当我使用该应用程序时，我设法输入答案，但当我点击进入或C按钮时，应用程序崩溃。任何想法？（我是新手，我希望我明白你对我说的话：P）谢谢！

Main xml：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_display_message"
android:layout_width="match_parent"
android:layout_height="match_parent"

tools:context="com.example.miltos.maths.DisplayMessageActivity">

<include
    android:id="@id/toolbar"
    layout="@layout/tool_bar"
    />

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:background="#84b3e7">

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:orientation="horizontal">

        <ImageView
            android:id="@+id/response"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:contentDescription="result"
            android:src="@drawable/tick"
            android:layout_gravity="bottom|left" />





    </LinearLayout>

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:orientation="horizontal" >


        <TextView
            android:id="@+id/question"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_marginBottom="2dp"
            android:layout_marginLeft="2dp"
            android:layout_marginTop="2dp"
            android:layout_weight="1"
            android:background="#dfeaf1"
            android:gravity="center|right"
            android:padding="5dp"
            android:text="0 + 0"
            android:textColor="#ff333333"
            android:textSize="30sp" />

        <TextView
            android:id="@+id/answer"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_marginBottom="2dp"
            android:layout_marginRight="2dp"
            android:layout_marginTop="2dp"
            android:layout_weight="1"
            android:background="#dfeaf1"
            android:gravity="center|left"
            android:padding="5dp"
            android:text="= ?"
            android:textColor="#ff333333"
            android:textSize="30sp" />

        <Button
            android:id="@+id/clear"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_margin="1dp"
            android:layout_weight="1"
            android:background="#dfeaf1"
            android:gravity="center"
            android:padding="5dp"
            android:text="C"
            android:textColor="#ff333333"
            android:textSize="30sp"
            android:textStyle="bold" />



    </LinearLayout>

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:orientation="horizontal" >

        <Button
            android:id="@+id/btn7"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_margin="1dp"
            android:layout_weight="1"
            android:background="#86959f"
            android:gravity="center"
            android:padding="5dp"
            android:tag="7"
            android:text="7"
            android:textColor="#ffcccccc"
            android:textSize="30sp"
            android:textStyle="bold" />

        <Button
            android:id="@+id/btn8"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_margin="1dp"
            android:layout_weight="1"
            android:background="#86959f"
            android:gravity="center"
            android:padding="5dp"
            android:tag="8"
            android:text="8"
            android:textColor="#ffcccccc"
            android:textSize="30sp"
            android:textStyle="bold" />

        <Button
            android:id="@+id/btn9"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_margin="1dp"
            android:layout_weight="1"
            android:background="#86959f"
            android:gravity="center"
            android:padding="5dp"
            android:tag="9"
            android:text="9"
            android:textColor="#ffcccccc"
            android:textSize="30sp"
            android:textStyle="bold" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:orientation="horizontal" >

        <Button
            android:id="@+id/btn4"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_margin="1dp"
            android:layout_weight="1"
            android:background="#86959f"
            android:gravity="center"
            android:padding="5dp"
            android:tag="4"
            android:text="4"
            android:textColor="#ffcccccc"
            android:textSize="30sp"
            android:textStyle="bold" />

        <Button
            android:id="@+id/btn5"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_margin="1dp"
            android:layout_weight="1"
            android:background="#86959f"
            android:gravity="center"
            android:padding="5dp"
            android:tag="5"
            android:text="5"
            android:textColor="#ffcccccc"
            android:textSize="30sp"
            android:textStyle="bold" />

        <Button
            android:id="@+id/btn6"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_margin="1dp"
            android:layout_weight="1"
            android:background="#86959f"
            android:gravity="center"
            android:padding="5dp"
            android:tag="6"
            android:text="6"
            android:textColor="#ffcccccc"
            android:textSize="30sp"
            android:textStyle="bold" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:orientation="horizontal" >

        <Button
            android:id="@+id/btn1"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_margin="1dp"
            android:layout_weight="1"
            android:background="#86959f"
            android:gravity="center"
            android:padding="5dp"
            android:tag="1"
            android:text="1"
            android:textColor="#ffcccccc"
            android:textSize="30sp"
            android:textStyle="bold" />

        <Button
            android:id="@+id/btn2"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_margin="1dp"
            android:layout_weight="1"
            android:background="#86959f"
            android:gravity="center"
            android:padding="5dp"
            android:tag="2"
            android:text="2"
            android:textColor="#ffcccccc"
            android:textSize="30sp"
            android:textStyle="bold" />

        <Button
            android:id="@+id/btn3"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_margin="1dp"
            android:layout_weight="1"
            android:background="#86959f"
            android:gravity="center"
            android:padding="5dp"
            android:tag="3"
            android:text="3"
            android:textColor="#ffcccccc"
            android:textSize="30sp"
            android:textStyle="bold" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:orientation="horizontal" >

        <Button
            android:id="@+id/btn0"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_margin="1dp"
            android:layout_weight="1"
            android:background="#86959f"
            android:gravity="center"
            android:padding="5dp"
            android:tag="0"
            android:text="0"
            android:textColor="#ffcccccc"
            android:textSize="30sp"
            android:textStyle="bold" />

        <Button
            android:id="@+id/enter"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_margin="1dp"
            android:layout_weight="2"
            android:background="#86959f"
            android:gravity="center"
            android:padding="5dp"
            android:text="Enter"
            android:textColor="#ff333333"
            android:textSize="30sp"
            android:textStyle="bold" />
    </LinearLayout>





</LinearLayout>

</RelativeLayout>

Java代码：

public class DisplayMessageActivity extends AppCompatActivity implements OnClickListener

{
private int level = 0,answer = 0, operator = 0, operand1 = 0, operand2 = 0;
private final int ADD_OPERATOR = 0, SUBTRACT_OPERATOR = 1, MULTIPLY_OPERATOR = 2, DIVIDE_OPERATOR = 3;
private String[] operators = {"+", "-", "x", "/"};
private int[][] levelMax = {
        {10, 25, 50},
        {10, 20, 30},
        {5, 10, 15},
        {10, 50, 100}};
private Random random;
private TextView question, answerTxt;
private ImageView response;
private Button btn1, btn2, btn3, btn4, btn5, btn6, btn7, btn8, btn9, btn0, enterBtn, clearBtn;

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

    question =  (TextView)findViewById(R.id.question);
    answerTxt = (TextView)findViewById(R.id.answer);
    response =  (ImageView)findViewById(R.id.response);
    response.setVisibility(View.INVISIBLE);
    btn1 = (Button)findViewById(R.id.btn1);
    btn2 = (Button)findViewById(R.id.btn2);
    btn3 = (Button)findViewById(R.id.btn3);
    btn4 = (Button)findViewById(R.id.btn4);
    btn5 = (Button)findViewById(R.id.btn5);
    btn6 = (Button)findViewById(R.id.btn6);
    btn7 = (Button)findViewById(R.id.btn7);
    btn8 = (Button)findViewById(R.id.btn8);
    btn9 = (Button)findViewById(R.id.btn9);
    btn0 = (Button)findViewById(R.id.btn0);
    enterBtn = (Button)findViewById(R.id.enter);
    clearBtn = (Button)findViewById(R.id.clear);
    btn1.setOnClickListener(this);
    btn2.setOnClickListener(this);
    btn3.setOnClickListener(this);
    btn4.setOnClickListener(this);
    btn5.setOnClickListener(this);
    btn6.setOnClickListener(this);
    btn7.setOnClickListener(this);
    btn8.setOnClickListener(this);
    btn9.setOnClickListener(this);
    btn0.setOnClickListener(this);
    enterBtn.setOnClickListener(this);
    clearBtn.setOnClickListener(this);
    Bundle extras = getIntent().getExtras();
    if(extras != null)
    {
        int passedLevel = extras.getInt("level", -1);
        if(passedLevel>=0) level = passedLevel;
    }

    random = new Random();
    chooseQuestion();
}
private void chooseQuestion(){
    answerTxt.setText("= ?");
    operator = random.nextInt(operators.length);
    operand1 = getOperand();
    operand2 = getOperand();

    if(operator == SUBTRACT_OPERATOR){
        while(operand2>operand1){
            operand1 = getOperand();
            operand2 = getOperand();
        }
    }

    else if(operator==DIVIDE_OPERATOR){
        while((((double)operand1/(double)operand2)%1 > 0) || (operand1==operand2))
        {
            operand1 = getOperand();
            operand2 = getOperand();
        }
    }
    switch(operator)
    {
        case ADD_OPERATOR:
            answer = operand1+operand2;
            break;
        case SUBTRACT_OPERATOR:
            answer = operand1-operand2;
            break;
        case MULTIPLY_OPERATOR:
            answer = operand1*operand2;
            break;
        case DIVIDE_OPERATOR:
            answer = operand1/operand2;
            break;
        default:
            break;
    }
    question.setText(operand1+" "+operators[operator]+" "+operand2);
}
private int getOperand(){
    return random.nextInt(levelMax[operator][level] - levelMax[operator][level] + 1)
            + levelMax[operator][level];

}




@Override
public void onClick(View view) {

    if(view.getId()==R.id.enter){
        String answerContent = answerTxt.getText().toString();
        if(!answerContent.endsWith("?"))
        {
            int enteredAnswer = Integer.parseInt(answerContent.substring(2));
            if(enteredAnswer==answer){

                response.setImageResource(R.drawable.tick);
                response.setVisibility(View.VISIBLE);

            }
            else{
                response.setImageResource(R.drawable.cross);
                response.setVisibility(View.VISIBLE);
            }
            chooseQuestion();
        }

    }
    else if(view.getId()==R.id.clear){
        answerTxt.setText("= ?");
    }
    else {
        response.setVisibility(View.INVISIBLE);
    }

    int enteredNum = Integer.parseInt(view.getTag().toString());

    if(answerTxt.getText().toString().endsWith("?"))
        answerTxt.setText("= "+enteredNum);
    else
        answerTxt.append(""+enteredNum);
}
}

错误日志：

01-16 16:04:35.300 4578-4614/com.example.miltos.maths E/EGL_emulation: tid 4614: eglSurfaceAttrib(1146): error 0x3009 (EGL_BAD_MATCH)
01-16 16:04:37.016 4578-4614/com.example.miltos.maths E/EGL_emulation: tid     4614: eglSurfaceAttrib(1146): error 0x3009 (EGL_BAD_MATCH)
01-16 16:04:39.157 4578-4578/com.example.miltos.maths E/AndroidRuntime: FATAL EXCEPTION: main
                                                                    Process:  com.example.miltos.maths, PID: 4578
                                                                    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
                                                                        at com.example.miltos.maths.DisplayMessageActivity.onClick(DisplayMessageActivity.java:156)
                                                                        at android.view.View.performClick(View.java:5610)
                                                                        at android.view.View$PerformClick.run(View.java:22265)
                                                                        at android.os.Handler.handleCallback(Handler.java:751)
                                                                        at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                        at android.os.Looper.loop(Looper.java:154)
                                                                        at android.app.ActivityThread.main(ActivityThread.java:6077)
                                                                        at java.lang.reflect.Method.invoke(Native Method)
                                                                        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
                                                                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)

Answer 1

在代码中添加以下内容

btn1.setTag('1');
btn2.setTag('2');
btn3.setTag('3');
btn4.setTag('4');

同样适用于所有10个按钮，并尝试运行您发布的相同代码。

Answer 2

您已将onClick回调功能绑定到所有按钮，包括enter和clear按钮。但是，以下代码行导致了问题

int enteredNum = Integer.parseInt(view.getTag().toString());

尝试获取UI元素中的输入并将其分配给enteredNum，这在输入UI元素上非常有意义，但在enter和clear按钮上则没有。因此，您将获得NullPointerException，因为没有值可供阅读。

我建议采用以下方法。创建e onClick回调并按如下方式分配它们：

输入字段中的一个。
一个在你的＆＃34;输入＆＃34;按钮。
一个在你的＆＃34;清除＆＃34;按钮。

这将清楚地表明，当点击enter按钮时，您不想阅读任何内容。

通过这种方式，您可以分离每个按钮的业务逻辑。除了解决您的问题，对于初级开发人员来说，这将是一个很好的做法。

我还建议在不同的类中开始将代码分区，作为一般原则，以便更容易阅读和特别维护。在第一章中涵盖这些原则的优秀读物是Clean Code by Robert C. Martin。

如果您的申请问题仍然存在，请随时告诉我。

Android应用程序数学游戏崩溃

2 个答案: