我正在尝试将输入验证添加到文本框中，以确保如果用户输入除我的标签之外的任何其他内容，则会说＆＃34;仅输入一个数字。＆＃34;我尝试过使用＆＃39; if＆＃39;这个声明（看下面的代码），但它没有用。而不是将消息发布到＆＃34;输入一个数字＆＃34;我的程序崩溃时出现此错误消息
＆＃39; System.FormatException＆＃39;：输入字符串的格式不正确
我是菜鸟，所以我不确定如何解决这个问题。
命名空间计算器 { public partial class frmCalculator：Form { public frmCalculator（） { 的InitializeComponent（）; }
string name = "";//Stores the Name typed into the text box
string classType = "";//Stores the Class typed into the text box
decimal grade;// Stores the Grade typed into the text box
private void btnSubmit_Click(object sender, EventArgs e)
{
classType = txtBoxClass.Text;
grade = Convert.ToDecimal(txtBoxGrade.Text);
name = txtBoxName.Text;
switch (classType)
{
//Case for Math class and grade comparison
case "m":
case "M":
if (grade >= -1 && grade <= 100)
{
if (grade >= 94)
{
lblAnswer.Text = name + "'s grade in Math is an A";
}
if (grade <= 93)
{
lblAnswer.Text = name + "'s grade in Math is an A-";
}
if (grade <= 89)
{
lblAnswer.Text = name + "'s grade in Math is a B+";
}
if (grade <= 86)
{
lblAnswer.Text = name + "'s grade in Math is an B";
}
if (grade <= 83)
{
lblAnswer.Text = name + "'s grade in Math is a B-";
}
if (grade <= 79)
{
lblAnswer.Text = name + "'s grade in Math is a C+";
}
if (grade <= 76)
{
lblAnswer.Text = name + "'s grade in Math is a C";
}
if (grade <= 73)
{
lblAnswer.Text = name + "'s grade in Math is a C-";
}
if (grade <= 69)
{
lblAnswer.Text = name + "'s grade in Math is a D";
}
if (grade < 65)
{
lblAnswer.Text = name + "'s grade in Math is an F";
}
//Clears the text boxes when the Submit button is clicked.
txtBoxName.Text = "";
txtBoxClass.Text = "";
txtBoxGrade.Text = "";
}
else { lblAnswer.Text = "Input a number!"; }
break;
//Case for Science class and grade comparison
case "s":
case "S":
if (grade >= 94)
{
lblAnswer.Text = name + "'s grade in Science is an A";
}
if (grade <= 93)
{
lblAnswer.Text = name + "'s grade in Science is an A-";
}
if (grade <= 89)
{
lblAnswer.Text = name + "'s grade in Science is a B+";
}
if (grade <= 86)
{
lblAnswer.Text = name + "'s grade in Science is an B";
}
if (grade <= 83)
{
lblAnswer.Text = name + "'s grade in Science is a B-";
}
if (grade <= 79)
{
lblAnswer.Text = name + "'s grade in Science is a C+";
}
if (grade <= 76)
{
lblAnswer.Text = name + "'s grade in Science is a C";
}
if (grade <= 73)
{
lblAnswer.Text = name + "'s grade in Science is a C-";
}
if (grade <= 69)
{
lblAnswer.Text = name + "'s grade in Science is a D";
}
if (grade < 65)
{
lblAnswer.Text = "'s grade in Science is an F";
}
//Clears the text boxes when the Submit button is clicked.
txtBoxName.Text = "";
txtBoxClass.Text = "";
txtBoxGrade.Text = "";
break;
//Case for English class and grade comparison.
case "e":
case "E":
if (grade >= 94)
{
lblAnswer.Text = name + "'s grade in English is an A";
}
if (grade <= 93)
{
lblAnswer.Text = name + "'s grade in English is an A-";
}
if (grade <= 89)
{
lblAnswer.Text = name + "'s grade in English is a B+";
}
if (grade <= 86)
{
lblAnswer.Text = name + "'s grade in English is an B";
}
if (grade <= 83)
{
lblAnswer.Text = name + "'s grade in English is a B-";
}
if (grade <= 79)
{
lblAnswer.Text = name + "'s grade in English is a C+";
}
if (grade <= 76)
{
lblAnswer.Text = name + "'s grade in English is a C";
}
if (grade <= 73)
{
lblAnswer.Text = name + "'s grade in English is a C-";
}
if (grade <= 69)
{
lblAnswer.Text = name + "'s grade in English is a D";
}
if (grade < 65)
{
lblAnswer.Text = name + "'s grade in English is an F";
}
//Clears the text boxes when the Submit button is clicked.
txtBoxName.Text = "";
txtBoxClass.Text = "";
txtBoxGrade.Text = "";
break;
default:
lblAnswer.Text = "Invalid Class type! Enter M for Math, S for Science or \nE for English only.";
txtBoxClass.Text = "";//Clears just the Class text box.
break;
}
}
private void btnExit_Click(object sender, EventArgs e)
{
//Exits the application when the Exit button is clicked.
this.Close();
}
}
}
答案 0 :(得分：6)
您应该使用数字基元的TryParse方法来查看是否可以将输入转换为数字。
decimal grade;
if (Decimal.TryParse(txtBoxGrade.Text, out grade)) {
// Its a valid number - the rest of your code goes here
// and uses the grade variable as the number you want.
} else {
// Its not a valid number
lblAnswer.Text = "Input a number only.";
}
答案 1 :(得分：1)
使用Decimal.TryParse检查输入文本是否为小数而不抛出异常（如果不是）。
if(Decimal.TryParse(txtBoxGrade.Text, out grade))
{
// Your code
}
else
{
lblAnswer.Text = "Input a number!";
}
答案 2 :(得分：0)
您可以使用TryParse查看它是否为数字。
decimal grade;
if(!decimal.TryParse(txtBoxGrade.Text, out grade))
{
MessageBox.Show(string.Format("Unable to parse '{0}'.", txtBoxGrade.Text));
return;
}
答案 3 :(得分：0)
请尝试以下操作。您可以使下面的代码更好。无论如何，保持改进尽可能接近你的代码，你可以做出几点改进： -
以下代码可以为您提供帮助。
private void btnSubmit_Click(object sender, EventArgs e)
{
var classType = txtBoxClass.Text;
var name = txtBoxName.Text;
decimal grade;
if (! decimal.TryParse(txtBoxGrade.Text, out grade))
{
lblAnswer.Text = "Input a number!";
return;
}
switch (classType)
{
//Case for Math class and grade comparison
case "m":
case "M":
if (grade > -1 && grade <= 100)
{
if (grade >= 94)
{
lblAnswer.Text = name + "'s grade in Math is an A";
}
else if (grade <= 93)
{
lblAnswer.Text = name + "'s grade in Math is an A-";
}
else if (grade <= 89)
{
lblAnswer.Text = name + "'s grade in Math is a B+";
}
else if (grade <= 86)
{
lblAnswer.Text = name + "'s grade in Math is an B";
}
else if (grade <= 83)
{
lblAnswer.Text = name + "'s grade in Math is a B-";
}
else if (grade <= 79)
{
lblAnswer.Text = name + "'s grade in Math is a C+";
}
else if (grade <= 76)
{
lblAnswer.Text = name + "'s grade in Math is a C";
}
else if (grade <= 73)
{
lblAnswer.Text = name + "'s grade in Math is a C-";
}
else if (grade <= 69)
{
lblAnswer.Text = name + "'s grade in Math is a D";
}
else if (grade < 65)
{
lblAnswer.Text = name + "'s grade in Math is an F";
}
//Clears the text boxes when the Submit button is clicked.
txtBoxName.Text = "";
txtBoxClass.Text = "";
txtBoxGrade.Text = "";
}
else { lblAnswer.Text = "Input a number between 0 and 100!"; }
break;
}
}