C# wpf calculator

我正在制作一个计算器，但当我试图用十进制数字进行计算时，我遇到了一个异常。所有sum1 += double.Parse(numEnt.Text);都有问题但我现在有点迷路了：P

    public partial class MainWindow : Window
{
    double sum1 = 0;
    double sum2 = 0;
    string dotSign = "";
    bool plusButtonClicked = false;
    bool subButtonClicked = false;
    bool multButtonClicked = false;
    bool divButtonClicked = false;

    public MainWindow()
    {
        InitializeComponent();
    }
    private void NumberValidationTextBox(object sender, TextCompositionEventArgs e)
    {
        Regex regex = new Regex("[^0-9]+");
        e.Handled = regex.IsMatch(e.Text);
    }
    private void one_Click(object sender, RoutedEventArgs e)
    {
        numEnt.Text += one.Content;
    }
    private void two_Click(object sender, RoutedEventArgs e)
    {
        numEnt.Text += two.Content;
    }
    private void three_Click(object sender, RoutedEventArgs e)
    {
        numEnt.Text += three.Content;
    }
    private void four_Click(object sender, RoutedEventArgs e)
    {
        numEnt.Text += four.Content;
    }
    private void five_Click(object sender, RoutedEventArgs e)
    {
        numEnt.Text += five.Content;
    }
    private void six_Click(object sender, RoutedEventArgs e)
    {
        numEnt.Text += six.Content;
    }
    private void seven_Click(object sender, RoutedEventArgs e)
    {
        numEnt.Text += seven.Content;
    }
    private void eight_Click(object sender, RoutedEventArgs e)
    {
        numEnt.Text += eight.Content;
    }
    private void nine_Click(object sender, RoutedEventArgs e)
    {
        numEnt.Text += nine.Content;
    }
    private void zero_Click(object sender, RoutedEventArgs e)
    {
        numEnt.Text += zero.Content;
    }
    private void add_Click(object sender, RoutedEventArgs e)
    {
        sum1 += double.Parse(numEnt.Text);
        numEnt.Clear();
        plusButtonClicked = true;
        subButtonClicked = false;
        multButtonClicked = false;
        divButtonClicked = false;
    }
    private void sub_Click(object sender, RoutedEventArgs e)
    {
        sum1 += double.Parse(numEnt.Text);
        numEnt.Clear();
        plusButtonClicked = false;
        subButtonClicked = true;
        multButtonClicked = false;
        divButtonClicked = false;
    }
    private void mult_Click(object sender, RoutedEventArgs e)
    {
        sum1 += double.Parse(numEnt.Text);
        numEnt.Clear();
        plusButtonClicked = false;
        subButtonClicked = false;
        multButtonClicked = true;
        divButtonClicked = false;
    }
    private void div_Click(object sender, RoutedEventArgs e)
    {
        sum1 = Convert.ToDouble(dotSign);
        sum1 += double.Parse(numEnt.Text);
        numEnt.Clear();
        plusButtonClicked = false;
        subButtonClicked = false;
        multButtonClicked = false;
        divButtonClicked = true;
    }
    public void deci_Click(object sender, RoutedEventArgs e)
    {
        double currentInput = numEnt.Text.Length;
        bool pointFound = false;
        /*for (int i = 0; i < currentInput.Length; i++)
        {
            if (currentInput[i] == '.')
                pointFound = true;
        }*/
        if (pointFound == false)
            numEnt.Text += ".";
    }
    private void equal_Click(object sender, RoutedEventArgs e)
    {
        if (plusButtonClicked == true)
        {
            sum2 = sum1 + double.Parse(numEnt.Text);
            result.Text = sum2.ToString();
            sum1 = 0;
        }
        if (subButtonClicked == true)
        {
            sum2 = sum1 - double.Parse(numEnt.Text);
            result.Text = sum2.ToString();
            sum1 = 0;
        }
        if (multButtonClicked == true)
        {
            sum2 = sum1 * double.Parse(numEnt.Text);
            result.Text = sum2.ToString();
            sum1 = 0;
        }
        if (divButtonClicked == true)
        {
            sum2 = sum1 / double.Parse(numEnt.Text);
            result.Text = sum2.ToString();
            sum1 = 0;
        }
        numEnt.Clear();
    }
    private void clear_Click(object sender, RoutedEventArgs e)
    {
        numEnt.Clear();
        calculations.Clear();
        result.Clear();
    }
    private void change_Click(object sender, RoutedEventArgs e)
    {
        double signchange = numEnt.Text.Length;
        signchange = -signchange;
        numEnt.Text = signchange.ToString();
    }


  }
}