User Input

User interface contains two types of user input controls: TextInput, which accepts all characters and NumericInput, which accepts only digits.

Implement the class TextInput that contains:

Public sub Add(c As Char) - adds the given character to the current value
Public function GetValue() As String - returns the current value

Implement the class NumericInput that:

Inherits TextInput
Overrides the Add method so that each non-numeric character is ignored

For example, the following code should output "10":

Dim input As TextInput = New NumericInput()
input.Add(CChar("1"))
input.Add(CChar("a"))
input.Add(CChar("0"))
Console.WriteLine(input.GetValue())

VB.NET 16.0, .NET Framework 4.7

Show starting code

Imports System

Module Module1
    Public Class TextInput
    
    End Class
    
    Public Class NumericInput
        
    End Class
    
    Public Sub Main()
        'Dim input As TextInput = New NumericInput()
        'input.Add(CChar("1"))
        'input.Add(CChar("a"))
        'input.Add(CChar("0"))
        'Console.WriteLine(input.GetValue())
    End Sub
End Module

Example case: System.InvalidCastException
Adding various characters to TextInput: System.NullReferenceException
Adding numeric characters to NumericInput: System.InvalidCastException
Adding various characters to NumericInput: System.InvalidCastException

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