vb.net - 为什么 Try/Catch 在数字类型中不起作用？

Question

Dim mynumber as Integer 'This is the variable as an integer, (Integers only allow WHOLE numbers)

Console.WriteLine("Enter your number..") 'Ask to enter number
    Try
        mynumber = Console.ReadLine 'Read user input and store it
    Catch
        Console.WriteLine()
        Console.ForegroundColor = ConsoleColor.Red
        Console.WriteLine("Only whole numbers allowed! Press enter to start again!")
        Console.ResetColor()
        Console.ReadLine()
        Console.Clear()
        GoTo start
    End Try

好的，伙计们，正如您从上面的示例中看到的，我已经设置了一个 Try/Catch 来进行错误处理。我遇到了一个问题。是的，Try/Catch 代码会阻止输入字母(字符串)，但当我输入十进制数字时，它仍然接受它。为什么？如何防止这种情况发生？小数不应该被接受，因为整数只接受整数!

谢谢。

Answer 1

数字类型之间存在隐式转换，因此不会触发错误。有多种方法可以了解确切的数字类型。我想这里最好的选择是以下代码行:

Dim mynumber0 As Double 'This is the variable as an integer, (Integers only allow WHOLE numbers)
Dim wasOK As Boolean = True
Console.WriteLine("Enter your number..") 'Ask to enter number
Try
    mynumber0 = Console.ReadLine 'Read user input and store it
    If (Convert.ToInt32(mynumber0) <> mynumber0) Then
        wasOK = False
    End If
Catch
    wasOK = False
End Try

Dim mynumber As Integer = mynumber0
If (Not wasOK) Then
    Console.WriteLine()
    Console.ForegroundColor = ConsoleColor.Red
    Console.WriteLine("Only whole numbers allowed! Press enter to start again!")
    Console.ResetColor()
    Console.ReadLine()
    Console.Clear()
    GoTo start
End If

更新

TryParse 替代方案，按照 mafafu 的建议

Dim mynumber As Integer 'This is the variable as an integer, (Integers only allow WHOLE numbers)
Console.WriteLine("Enter your number..") 'Ask to enter number
If (Not Integer.TryParse(Console.ReadLine, mynumber)) Then
    Console.WriteLine()
    Console.ForegroundColor = ConsoleColor.Red
    Console.WriteLine("Only whole numbers allowed! Press enter to start again!")
    Console.ResetColor()
    Console.ReadLine()
    Console.Clear()
    GoTo start
End If