检查用户决定是否正确

Question

我目前正在做一个学校项目（一个小型​​ android 游戏），到目前为止，我已经编写了一个代码，它会在活动 InGame 启动后 2 秒生成一个 random equation 并在 @987654323 中显示它@。再过 5 秒后，第二个等式生成并显示在不同的文本视图中。现在用户必须通过按下按钮bigger 或smaller 来决定第二个等式的结果是否比第一个更大。如果它是正确的，应该显示下一个方程，它会像这样继续下去，直到用户判断错误。 到目前为止，这是我的代码： （第一个方程的代码）：

// Generate random equation and display it in textview

String[] operationSet = new String[]{"+", "-", "/", "*"};
String equation;
static double doubleAnswer1;
public void start1() {
    Random random = new Random();
    int numOfOperations = random.nextInt(2) + 1;

    List<String> operations = new ArrayList<>();

    for (int i = 0; i < numOfOperations; i++) {
        String operation = operationSet[random.nextInt(4)];
        operations.add(operation);
    }

    int numOfNumbers = numOfOperations + 1;
    List<Integer> numbers = new ArrayList<>();

    for (int i = 0; i < numOfNumbers; i++) {
        int number = random.nextInt(10)+1;
        numbers.add(number);
    }

    String equation = "";
    for (int i = 0; i < numOfOperations; i++) {
        equation += numbers.get(i);
        equation += operations.get(i);
    }
    equation += numbers.get(numbers.size() -1);

    TextView TextEquation = (TextView)findViewById(R.id.textView_first_equation);
    TextEquation.setText(equation);

    // Evaluate the result of the equation

    double doubleAnswer1 = eval(equation);

    String stringAnswer = Double.toString(doubleAnswer1);

    TextView textAnswer = (TextView)findViewById(R.id.textView4);
    textAnswer.setText(stringAnswer);
}

（第二个等式的代码（与第一个等式基本相同，只是字符串和双打的名称不同））：

String equation2;
static double doubleAnswer2;
public void start2() {
    Random random = new Random();
    int numOfOperations = random.nextInt(2) + 1;

    List<String> operations = new ArrayList<>();

    for (int i = 0; i < numOfOperations; i++) {
        String operation = operationSet[random.nextInt(4)];
        operations.add(operation);
    }

    int numOfNumbers = numOfOperations + 1;
    List<Integer> numbers = new ArrayList<>();

    for (int i = 0; i < numOfNumbers; i++) {
        int number = random.nextInt(10)+1;
        numbers.add(number);
    }

    String equation2 = "";
    for (int i = 0; i < numOfOperations; i++) {
        equation2 += numbers.get(i);
        equation2 += operations.get(i);
    }
    equation2 += numbers.get(numbers.size() -1);

    TextView TextEquation = (TextView)findViewById(R.id.textView3);
    TextEquation.setText(equation2);

    // Evaluate the result of the equation

    double doubleAnswer2 = eval(equation2);

    String stringAnswer = Double.toString(doubleAnswer2);

    TextView textAnswer = (TextView)findViewById(R.id.textView_result2);
    textAnswer.setText(stringAnswer);
}

这是我的 onCreate 代码：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.ingame);

    // Display first equation 2 seconds after the activity is launched

    final Handler handler1 = new Handler();
    handler1.postDelayed(new Runnable() {
        @Override
        public void run() {
            start1();
        }
    }, 2000);

    final Handler handler2 = new Handler();
    handler2.postDelayed(new Runnable() {
        @Override
        public void run() {
            start2();
        }
    }, 7000);

    // Check if user was right or wrong

    final Button buttonBigger = (Button)findViewById(R.id.button_bigger);
    final Button buttonSmaller = (Button)findViewById(R.id.button_smaller);

    View.OnClickListener listener = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if(v.equals(buttonBigger) && doubleAnswer1 < doubleAnswer2) {
                Log.v("TAG", "you are right");
            } else if(v.equals(buttonSmaller) && doubleAnswer1 > doubleAnswer2) {
                Log.v("TAG", "you are right");
            } else {
                Log.v("TAG", "you are wrong");
            }
        }
    };

    buttonBigger.setOnClickListener(listener);
    buttonSmaller.setOnClickListener(listener);
}

应用程序启动正确，它还显示first and second 等式，但是当我按下其中一个按钮时，它会在logcat you are wrong 中告诉我，但我决定100% 正确。但是，如果我调试应用程序，它会告诉我 doubleAnswer1 和 doubleAnswer2 是 both = 0. 这就是为什么它总是告诉我“你错了”。我不知道如何解决这个问题，也许我需要将 doubleAnswer1 和 doubleAnswer2 存储在某个地方。 我真的不知道该怎么做，所以如果有人知道该怎么做，那真的会帮助我。

如果我的问题有任何不清楚的地方，请随时提出，我会尽力澄清问题。

提前感谢您的帮助！

Answer 1

我认为你的问题出在这里：

double doubleAnswer1 = eval(equation);

我在互联网上进行了快速搜索，但没有找到任何名为 eval() 的本机函数。相反，您应该查看 Script Engine Manager for java：

ScriptEngineManager mgr = new ScriptEngineManager();
ScriptEngine engine = mgr.getEngineByName("JavaScript");
String foo = "40+2";
System.out.println(engine.eval(foo));

或此处显示的 exp4j： Executing math equation in Android

编辑： 更改以下内容：

double doubleAnswer1 = eval(equation);

到：

doubleAnswer1 = eval(equation);

对 doubleAnswer2 做同样的事情