Question

我试图在C＃中构建一个简单的计算器应用程序，我不知道为什么在执行以下步骤时它会崩溃。

输入0.2
点击减法
输入0

应用程序立即崩溃。我假设它与Zero（）函数有关，因为这是单击Zero按钮时执行的操作。条件语句用于处理不应像连续密码那样出现的情况。这是源代码。顺便说一句，其他数字的功能是相同的。

    public partial class MainWindow : Window
    {
        protected double firstNumber, secondNumber;
        protected string textBoxContents;
        protected int selectedFunction;
        public MainWindow()
        {
            InitializeComponent();
            firstNumber = 0;
            secondNumber = 0;
            selectedFunction = 0;
            textBoxContents = "0";
        }
        private void Zero(object sender, RoutedEventArgs e)
        {
            if (Convert.ToDouble(textBoxContents) > 0 || textBoxContents[textBoxContents.Length - 1] == '.')
            {
                if(selectedFunction != 0)
                    textBoxContents = textBoxContents + "0";
            }
            else if (textBoxContents == null)
            {
                textBoxContents = textBoxContents + "0";
            }
            ResultBox.Content = textBoxContents;
        }
        private void One(object sender, RoutedEventArgs e)
        {
            textBoxContents = textBoxContents + "1";
            ResultBox.Content = textBoxContents;
        }
        private void Decimal(object sender, RoutedEventArgs e)
        {
            textBoxContents = textBoxContents + ".";
            ResultBox.Content = textBoxContents;
        }
        private void Addition(object sender, RoutedEventArgs e)
        {
            firstNumber = Convert.ToDouble(textBoxContents);
            textBoxContents = null;
            selectedFunction = 1;
        }
        private void Subtraction(object sender, RoutedEventArgs e)
        {
            firstNumber = Convert.ToDouble(textBoxContents);
            textBoxContents = null;
            selectedFunction = 2;
        }
        private void Multiplication(object sender, RoutedEventArgs e)
        {
            firstNumber = Convert.ToDouble(textBoxContents);
            textBoxContents = null;
            selectedFunction = 3;
        }
        private void Division(object sender, RoutedEventArgs e)
        {
            firstNumber = Convert.ToDouble(textBoxContents);
            textBoxContents = null;
            selectedFunction = 4;
        }
        private void Result(object sender, RoutedEventArgs e)
        {
            secondNumber = Convert.ToDouble(textBoxContents);
            double thirdNumber = 0;
            switch (selectedFunction)
            {
                case 1:
                    thirdNumber = firstNumber + secondNumber;
                    break;
                case 2:
                    thirdNumber = firstNumber - secondNumber;
                    break;
                case 3:
                    thirdNumber = firstNumber * secondNumber;
                    break;
                case 4:
                    thirdNumber = firstNumber / secondNumber;
                    break;
                default:
                    break;
            }
            textBoxContents = Convert.ToString(thirdNumber);
            ResultBox.Content = textBoxContents;
        }
        private void ClearEverything(object sender, RoutedEventArgs e)
        {
            textBoxContents = null;
            firstNumber = 0;
            secondNumber = 0;
            selectedFunction = 1;
            ResultBox.Content = Convert.ToString(0);
        }
        private void ToggleNegative(object sender, RoutedEventArgs e)
        {
            if (Convert.ToDouble(textBoxContents) != 0)
            {
                textBoxContents = Convert.ToString(Convert.ToDouble(textBoxContents) * -1);
                ResultBox.Content = textBoxContents;
            }
            else
                ResultBox.Content = Convert.ToString(0);
        }
    }

Answer 1

小数点分隔符已本地化，您确定使用的是正确的文化（＆＃34;，＆＃34;而不是＆＃34;。＆＃34;）？

如果问题是这样，请查看此Stack Question

Answer 2

private void Zero(object sender, RoutedEventArgs e)
{
    if (Convert.ToDouble(textBoxContents) > 0 ||
        textBoxContents[textBoxContents.Length - 1] == '.')
    {
        if(selectedFunction != 0)
            textBoxContents = textBoxContents + "0";
    }
    else if (textBoxContents == null)
    {
        textBoxContents = textBoxContents + "0";
    }
    ResultBox.Content = textBoxContents;
}

这种逻辑看起来很糟糕。如果文本框的值为空，那么由于||另一侧的索引器，它会爆炸。我认为这可以改写为：

private void Zero(object sender, RoutedEventArgs e)
{
    var dblVal = Convert.ToDouble(textBoxContents.Text);
    textBoxContents.Text = dblVal.ToString();
    ResultBox.Content = textBoxContents.Text;
}

换句话说，如果文本框为空，则转化将产生0.0;如果它以1.结尾，则会产生1.0;如果它.5它会产生0.5。只需利用Convert。

Answer 3

单击减法按钮后，

textBoxContents为空。而不是textBoxContents = null;使用textBoxContents = "0";或textBoxContents = string.Empty;。为什么你把它设置为null呢？

在Zero方法中调用textBoxContents.Length会导致NullReferenceException。

正如其他人之前提到的那样，你在Zero（）中的逻辑接缝有点迂回，当然可能更小。

Answer 4

你正在做的减法功能

textBoxContents = null;

然后在零中你有

textBoxContents [textBoxContents.Length - 1]

这就是崩溃的原因

你应该在textBoxContents

上的任何操作之前检查null

计算器应用程序崩溃

4 个答案: