Object enter event "string to decimal not valid" - vb.net

Question

I have VB program which concatenates decimals of 2 categories, income and expenses.
For some reason incomeTextBox.Enter and expensesTextBox.Enter has weird behavior, saying:
Please enter numeric value for expenses
when I use either tab key or mouse to select other InputBox even after inputting an integer (which IsNumeric=True).
I also get error:
An unhandled exception of type 'System.InvalidCastException' occurred in Microsoft.VisualBasic.dll
Additional information: Conversion from string "" to type 'Decimal' is not valid.
Also, this is VB, not VB.Net, but there is no VB tag??
Option Explicit On
Public Class MainForm
Public decexpenses, decincome As Decimal
Public dectotalexpenses As Decimal = 0
Public dectotalincome As Decimal = 0
Private Sub MainForm_Load(sender As Object, e As EventArgs) Handles MyBase.Load
MsgBox("Use Enter key to enter values.")
End Sub
Private Sub expensesTextBox_Enter(sender As Object, e As EventArgs) Handles expensesTextBox.Enter
Dim expenses = expensesTextBox.Text
If IsNumeric(expenses) = False Then
MsgBox("Please enter numeric value for expenses.")
End If
expensesTextBox.Text = ""
decexpenses = CDec(expenses)
dectotalexpenses = decexpenses + dectotalexpenses
End Sub
Private Sub incomeTextBox_Enter(sender As Object, e As EventArgs) Handles incomeTextBox.Enter
Dim income = incomeTextBox.Text
If IsNumeric(income) = False Then
MsgBox("Please enter numeric value for income.")
ElseIf IsNumeric(income) = True Then
decincome = CDec(income)
dectotalincome = decincome + dectotalexpenses
End If
End Sub
End Class

Answer 1

I would instead of using Enter for the raise event I would use Text_Changed and use the KeyDown for Enter. Once the Text is Entered then they click enter on the textbox the routine will run Example the below:
Private Sub expensesTextBox_TextChanged(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles expensesTextBox.KeyDown
Dim dectotalexpenses As Decimal = 0
Dim dectotalincome As Decimal = 0
If e.KeyCode = Keys.Enter Then
Dim value As String = TextBox1.Text
Dim decincome As Decimal
If Not Decimal.TryParse(value, decincome) Then
MsgBox("Please enter numeric value for expenses.")
Return
End If
End If
End Sub

Answer 2

The Enter event is raised if the TextBox gets focus the first time, probably the text is empty at this point which raises your exception.
In your code you are also netiher using If...Else nor returning if the value is not numeric, so CDec(expenses) gets executed anyway which causes the exception. Also, instead of IsNumeric use Decimal.TryParse:
Private Sub expensesTextBox_Enter(sender As Object, e As EventArgs) Handles expensesTextBox.Enter
Dim value As String = expensesTextBox.Text
Dim decincome As Decimal
If Not Decimal.TryParse(value, decincome) Then
MsgBox("Please enter numeric value for expenses.")
Return
End If
dectotalexpenses = decincome + dectotalexpenses
End Sub
You should also use a different event like TextBox.TextChanged.