格式不正确的未处理字符串[重复]

Question

基本刷新了一些制作转换器的C#知识；我试图在textbox 中没有数字时弹出一个窗口，但是当我单击button 时出现此错误：

System.FormatException: '输入字符串的格式不正确。'

private void btnConvert_Click(object sender, EventArgs e)
    {

        // Killogram convertion

        double i = double.Parse(txtboxAmount.Text);
        if (comboBoxFrom.SelectedItem == "KG" && comboBoxTo.SelectedItem == "LB")
        {
            double conver = i * 2.20462262185;
            double converdec = Math.Round((Double)conver, 2);
            txtBoxResult.Text = "Converted Amount : " + converdec;
        }

        if (comboBoxFrom.SelectedItem == "LB" && comboBoxTo.SelectedItem == "KG")
        {
            double conver = i / 2.2046;
            double converdec = Math.Round((Double)conver, 2);
            txtBoxResult.Text = "Converted Amount : " + converdec;
        }

        if (comboBoxFrom.SelectedItem == "ST" && comboBoxTo.SelectedItem == "KG")
        {
            double conver = i * 6.35;
            double converdec = Math.Round((Double)conver, 2);
            txtBoxResult.Text = "Converted Amount : " + converdec;
        }

        // Pound convertion


        if (comboBoxFrom.SelectedItem == "LB" && comboBoxTo.SelectedItem == "ST")
        {
            double conver = i / 14;
            double converdec = Math.Round((Double)conver, 2);
            txtBoxResult.Text = "Converted Amount : " + converdec;
        }

        if (comboBoxFrom.SelectedItem == "ST" && comboBoxTo.SelectedItem == "LB")
        {
            double conver = i / 14;
            double converdec = Math.Round((Double)conver, 2);
            txtBoxResult.Text = "Converted Amount : " + converdec;
        }

        if (comboBoxFrom.SelectedItem == "LB" && comboBoxTo.SelectedItem == "KG")
        {
            double conver = i / 2.205;
            double converdec = Math.Round((Double)conver, 2);
            txtBoxResult.Text = "Converted Amount : " + converdec;
        }

        // Stone convertion

        if (comboBoxFrom.SelectedItem == "ST" && comboBoxTo.SelectedItem == "LB")
        {
            double conver = i * 14;
            double converdec = Math.Round((Double)conver, 2);
            txtBoxResult.Text = "Converted Amount : " + converdec;
        }

        if (comboBoxFrom.SelectedItem == "LB" && comboBoxTo.SelectedItem == "ST")
        {
            double conver = i / 14;
            double converdec = Math.Round((Double)conver, 2);
            txtBoxResult.Text = "Converted Amount : " + converdec;
        }

        if (comboBoxFrom.SelectedItem == "LB" && comboBoxTo.SelectedItem == "KG")
        {
            double conver = i / 2.205;
            double converdec = Math.Round((Double)conver, 2);
            txtBoxResult.Text = "Converted Amount : " + converdec;
        }

        else if (comboBoxFrom.SelectedItem == null && comboBoxTo.SelectedItem == null)
        {
            MessageBox.Show("Enter a valid weight amount and/or select a unit of measurement.");
        }

    }

导致问题的行在下面我把它变成一个带有 to string 但没有运气的字符串

double i = double.Parse(txtboxAmount.Text);

Answer 1

使用TryParse 优雅地失败：

var text = "123.4";

double result;

if (double.TryParse(text, out result))
{
    // do something
}

如果您使用法语系统并输入英文符号，则要考虑的另一件事可能是文化，

即. 而不是 , 它将无法解析您的输入。

if (double.TryParse(text, NumberStyles.Any, CultureInfo.CurrentCulture.NumberFormat, out result))
{
    // do something
}