CODEWITHSUNDEEP
vb.nettryparse
user1695704
user1695704

Reputation:

Conversion from string "" to type 'Double' is not valid using TryParse Method

I have a simple addition program in VB.Net and I am attempting to test if the textbox is only taking in a number and not any letters. I need to use the TryParse method, and I cannot figure out wny I am still receiving this error. Pls Help

Public Class perrySolutionForm
Dim numberOne As Double
Dim numberTwo As Double

Public Function sum(ByRef numberOne As Double, ByRef numberTwo As Double)
    sum = Val(numberOne) + Val(numberTwo)
End Function

Public Function difference(ByRef numberOne As Double, numberTwo As Double)     

difference = Val(numberOne) - Val(numberTwo)

End Function

Private Sub sumButton_Click(sender As Object, e As EventArgs) Handles sumButton.Click
    If numberOneInput.Text = "" Then
        MessageBox.Show("Both fields must be filled out.")
        If Double.TryParse(numberOneInput.Text, numberOne) Then
            MessageBox.Show("Success")
            'numberOne has a Double value
        Else
            MessageBox.Show("Failure")
            'numberOne = Nothing
        End If
    Else
        outputLabel.Text = sum(numberOne, numberTwo)
    End If
End Sub

Private Sub numberOneInput_TextChanged(sender As Object, e As EventArgs) Handles numberOneInput.TextChanged
    numberOne = numberOneInput.Text

End Sub

Private Sub numberTwoInput_TextChanged(sender As Object, e As EventArgs) Handles numberTwoInput.TextChanged
    numberTwo = numberTwoInput.Text

End Sub

Upvotes: 0

Views: 5487

Answers (1)

OneFineDay
OneFineDay

Reputation: 9024

This is how you use the TryParse:

If Double.TryParse(numberOneInput.Text, numberOne) Then
  'code for a success
  'numberOne has a Double value
Else
  'code for a failure
  'numberOne = Nothing
End If

End the code block if text is empty:

If String.IsNullOrWhiteSpace(numberOneInput.Text) Then 
   MessageBox.Show("Value is incorrect format")
   Exit Sub
End If

Upvotes: 1

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