How to clear Texboxes attached with message boxes in vb.net - vb.net

Question

For Learning the coding I built this application. It has Three text boxes.1 and 2 to enter numbers and 3 is to sum of 1 and 2. Button 2 is to get sum and 1 to clear textboxes.
Public Class Form1
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
End Sub
Private Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles TextBox1.TextChanged
If TextBox1.Text >= 101 Then
MsgBox("Enter numbers between 0 and 100")
End If
End Sub
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
TextBox3.Text = Int(TextBox1.Text) + Int(TextBox2.Text)
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
TextBox1.Clear()
TextBox2.Clear()
TextBox3.Clear()
End Sub
End Class
Here I have limited the TextBox1 to get numbers between 0 and 100. if it is over 100, displays a warning massage box.
When I click the clear button it gives an error. It doesn't clear. after deleting textbox 1 clearing code it works fine. I mean textbox 2 & 3 clear fine. There is a problem with Textbox 1. The reason i believe is the msgbox attached it. I need to keep Msgbox.
How do I clear them?

Answer 1

You need to suppress text changed event. See TextBoxBase.Clear Method
Public Class Form1
Private flag As Boolean
Private Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles TextBox1.TextChanged
' Check the flag to prevent code re-entry.
If flag = False Then
' Set the flag to True to prevent re-entry of the code below.
If TextBox1.Text >= 101 Then
MsgBox("Enter numbers between 0 and 100")
End If
End If
End Sub
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
TextBox3.Text = Int(TextBox1.Text) + Int(TextBox2.Text)
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
flag = True
TextBox1.Clear()
TextBox2.Clear()
TextBox3.Clear()
flag = False
End Sub
End Class

Answer 2

TextBox1.Clear() will fire TextBox1_TextChanged().
This line will do an implicit conversion from text to integer - it will fail with an error on blank or text entries:
If TextBox1.Text >= 101 Then
Instead, try this:
Dim number As Integer
If Int32.TryParse(TextBox1.Text, number) Then
If number >= 101 Then
MsgBox("Enter numbers between 0 and 100")
End If
End If