Decimal validation for textbox

Question

I want to validate a textbox like it accept only digits and a decimal point

 

Code Snippet

Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress

                       

If Not Char.IsDigit(e.KeyChar) And Not Char.IsControl(e.KeyChar) And Not Asc(e.KeyChar) = 46 Then

e.Handled = True

End If

 

now i need to restrict the textbox from entering more than one decimal point and it should display only two digits after the decimal point.

Answer 1

You could try something like the following.  If your data type is not Decimal, substitute the type you really want.  By using the correct type, this code will also prevent entry of too many digits for the data type.

 

Code Snippet

Private _PreviousKnownGoodText As String = ""

 

Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged

Dim dummy As Decimal

If TextBox1.Text <> "" AndAlso Not Decimal.TryParse(TextBox1.Text, _

System.Globalization.NumberStyles.AllowDecimalPoint, Nothing, dummy) Then

 

Dim savedCursorPosition As Integer = TextBox1.SelectionStart

TextBox1.Text = _PreviousKnownGoodText

If savedCursorPosition >= 1 Then

TextBox1.SelectionStart = savedCursorPosition - 1

End If

Else

_PreviousKnownGoodText = TextBox1.Text

End If

End Sub

 

Answer 2

Hi,

 

Typing something like

 

.34

 

is also valid.

 

Alter this line only if say you want 4 decimal places.>>

 

If decimalPlaces > 4 Then e.Handled = True

 

Code Snippet

 

Option Strict On

 

Public Class Form1

 

Dim decimalPlaces As Integer = 0

 

Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress

 

If TextBox1.Text.IndexOf(".") = 0 Then

TextBox1.Text = "0" & TextBox1.Text

TextBox1.SelectionStart = 2

End If

If TextBox1.Text.IndexOf(".") >= 0 Then

 

decimalPlaces = TextBox1.Text.Substring(TextBox1.Text.IndexOf(".")).Length

 

Else

decimalPlaces = 0

End If

 

If decimalPlaces > 2 Then e.Handled = True

 

If Not Char.IsDigit(e.KeyChar) And Not Char.IsControl(e.KeyChar) And TextBox1.Text.IndexOf(".") >= 0 Then

 

e.Handled = True

'Allow the Backspace key.

ElseIf e.KeyChar = Chr(Keys.Back) Then

e.Handled = False

End If

End Sub

 

Private Sub TextBox1_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged

 

Dim myDecimal As Decimal

Decimal.TryParse(TextBox1.Text, myDecimal)

Me.Text = myDecimal.ToString

End Sub

End Class

 

 

 

 

Regards,

 

John

 

Answer 3

Place the following code in the textbox's KeyPress event.  It will only allow a real number to be entered, including one decimal point, as well as either a positive or negative number.  It will only allow input of up to 2 digits past the decimal point.

 

 

Code Snippet

Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress

Dim dot As Integer, ch As String

If Not Char.IsDigit(e.KeyChar) Then e.Handled = True

If e.KeyChar = "-" And TextBox1.SelectionStart = 0 Then e.Handled = False 'allow negative number

If e.KeyChar = "." And TextBox1.Text.IndexOf(".") = -1 Then e.Handled = False 'allow single decimal point

dot = TextBox1.Text.IndexOf(".")

If dot > -1 Then 'allow only 2 decimal places

   ch = TextBox1.Text.Substring(dot + 1)

   If ch.Length > 1 Then e.Handled = True

End If

If e.KeyChar = Chr(13) Then TextBox2.Focus() 'Enter key moves to specified control, or:

'If e.KeyChar = Chr(13) Then GetNextControl(TextBox1, True).Focus() 'Enter key moves to next control in Tab order

If e.KeyChar = Chr(8) Then e.Handled = False 'allow Backspace

End Sub

 

 

 

 

Answer 4

One needs to be careful with the KeyPress solutions to this problem.  The user can still right-click and use the Paste command to paste text that does not conform to the validation.

 

A common solution is to have both a KeyPress and a TextChanged handler.

 

Answer 5

I added code to my above post to allow input of only 2 decimal places.  I also moved the line that allows the backspace key to the line before last, otherwise you can't backspace after attempting to enter a 3rd decimal place.  However, you  can't enter anything else after that unless you delete everything.

 

Answer 6

You will get the idea, how to restrict pasting into a textbox from this site

 

Windows Forms FAQ - Windows Forms TextBox.htm