The following VB.NET function NumericValidation is used to prevent the users from entering characters other than digits in text box
* Drag the TextBox Control and drop on Form and name it as TextBox1
* Call the function NumericValidation Whenever an key is pressed (KeyPress Event of Textbox)
/* This function accepts a single character entered in the text box as Input */
/* This function Permits Digits [0-9] */
/* This function permits a Single Dot for decimal value */
/* This function permits 4 digits after decimal point */
/* This function Permits a single - sign for Negative Symbol */
/* This function restricts Negative sign to be at the First Character */
/* This function does not permit 0 as first character */
VB.NET CODE
[CODE]
Private Function NumericValidation(ByVal chr As Char)
Dim index As Integer
Dim str As String = TextBox1.Text.Trim
'First Digit should not be 0
If chr = "0" And str = "" Then
Return False
End If
'Check for duplicate decimal digit
If (chr = ".") Then
index = str.IndexOf(".")
If (index > 0) Then
'Already dot is there
Return False
End If
End If
'Restrict 4 digit numbers after decimal point
index = str.IndexOf(".")
If (index > 0) Then
If (str.Length - index) > 4 Then
'Not More than 4 decimal digits after dot
If Not Char.IsControl(chr) Then 'To allow back space
Return False
End If
End If
End If
If Char.IsDigit(chr) Then 'If it is a digit allow
Return True
End If
If (chr = "-") Then '- (Negative) sign should come first
If (str.Length > 0) Then
Return False
End If
End If
If (Not Char.IsDigit(chr)) Then
' Non Digits are not allowed
If (Not (chr = ".") And Not (chr = "\b") And Not (chr = "-") And Not Char.IsControl(chr)) Then 'Other than back space or dot or negative sign
Return False
End If
End If
Return True
End Function
//Whenever an Key is Pressed We just need to call NumericValidation function with the Key pressed
Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress
'If the key entered does not meet the criteria
If Not NumericValidation(e.KeyChar) Then
e.Handled = True //Invalid value
Beep() //Beep sound
End If
End Sub
[/CODE]
Valid and Invalid Data
Valid Examples
-1.7897
23.7977
InValid Examples - Will not be permitted
A1235
0788
23.7.2
7-89
C# CODE
Add the Handler textBox1_KeyPress in the Entry Point
Whenever an Key is Pressed we have to Call NumericValidation with the pressed Character.
public Form1()
{
InitializeComponent();
//Add the handler for KeyPress Event for textbox
textBox1.KeyPress += new KeyPressEventHandler(textBox1_KeyPress);
}
//Whenever an Key is Pressed We just need to call NumericValidation function with the Key pressed
private void textBox1_KeyPress(Object sender, System.Windows.Forms.KeyPressEventArgs e)
{
if (!(NumericValidation(e.KeyChar))) 'If not valid do not allow
{
e.Handled = true;
}
}
//Numeric Validation Function
private bool NumericValidation(char chr)
{
string str = textBox1.Text.Trim();
int index = 0;
//First Digit should not be 0
if (chr == '0' & string.IsNullOrEmpty(str))
{
return false;
}
//Check for duplicate decimal digit
if ((chr == '.'))
{
index = str.IndexOf(".");
if ((index > 0))
{
//Already dot is there
return false;
}
}
//Restrict 4 digit numbers after decimal point
index = str.IndexOf(".");
if ((index > 0))
{
//Already dot is there
if ((str.Length - index) > 4)
{
//More than 4 decimal digits after dot
if (!char.IsControl(chr))
{
//To allow back space
return false;
}
}
}
if (char.IsDigit(chr))
{
return true;
}
if ((chr == '-'))
{
//- sign should come first
if ((str.Length > 0))
{
return false;
}
}
if ((!char.IsDigit(chr)))
{
// Non Digits are not allowed
if ((!(chr == '.') & !(chr == '\b') & !(chr == '-') & !char.IsControl(chr)))
{
//Other than back space or dot or negative sign
return false;
}
}
return true;
}
same code snippets available under http://www.dotnetspider.com/resources/29500-C-Numeric-Text-Box.aspx
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