如何验证我的文本框仅显示大于或等于0？

Question

I have one button to increment the value of the text box by 1 and another button to do the opposite. I want to know how to validate it so the number doesn't go below zero.

Here is the code I have so far:

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim i As Integer
    If Integer.TryParse(TextBox2.Text, i) Then
        i += 1
    Else
        i = 0
    End If
    TextBox2.Text = i.ToString()
End Sub

Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
    Dim i As Integer
    If Integer.TryParse(TextBox2.Text, i) Then
        i -= 1
    Else
        i = 0
    End If
    TextBox2.Text = i.ToString()
End Sub

Answer 1

You have two easy options:

• before you decrement the number, check if it is greater than zero
• after you decrement the number, check if is less than zero and if so, set it to zero.

So..

If Integer.TryParse(TextBox2.Text, i) AndAlso (i > 0) Then
        i -= 1
    Else

or...

If Integer.TryParse(TextBox2.Text, i) Then
        i -= 1
        If i < 0 Then
            i = 0
        End If
    Else

You could also use

i = Math.Max(0, i - 1)