In this article I will explain with an example, how to perform Date format validation (dd/MM/yyyy) using Regular Expression in C# and VB.Net.
The User will enter Date in TextBox and when the Button is clicked, the Date will be tested against the Regular Expression for dd/MM/yyyy format and if invalid, a Message Box will be displayed.
Form Design
The Form consists of a TextBox control and a Button. The Button has been assigned Click event handler.
![Date format (dd/MM/yyyy) validation using Regular Expression in C# and VB.Net]()
Namespaces
You will need to import the following namespace.
C#
using System.Globalization;
using System.Text.RegularExpressions;
VB.Net
Imports System.Globalization
Imports System.Text.RegularExpressions
Validate Date dd/MM/yyyy format in TextBox using Regular Expression in C# and VB.Net
When the Button is clicked, the Date from the TextBox is tested against the Regular Expression using the IsMatch function.
Once the dd/MM/yyyy format is validated, the Date is verified by converting to DateTime object using DateTime.TryParseExact function to make sure whether it is a valid date.
If the Date is found invalid an error message is displayed using MessageBox.
C#
private void btnValidate_Click(object sender, EventArgs e)
{
Regex regex = new Regex(@"(((0|1)[0-9]|2[0-9]|3[0-1])\/(0[1-9]|1[0-2])\/((19|20)\d\d))$");
//Verify whether date entered in dd/MM/yyyy format.
bool isValid = regex.IsMatch(txtDate.Text.Trim());
//Verify whether entered date is Valid date.
DateTime dt;
isValid = DateTime.TryParseExact(txtDate.Text, "dd/MM/yyyy", new CultureInfo("en-GB"), DateTimeStyles.None, out dt);
if (!isValid)
{
MessageBox.Show("Invalid Date.");
}
}
VB.Net
Private Sub btnValidate_Click(sender As System.Object, e As System.EventArgs) Handles btnValidate.Click
Dim regex As Regex = New Regex("(((0|1)[0-9]|2[0-9]|3[0-1])\/(0[1-9]|1[0-2])\/((19|20)\d\d))$")
'Verify whether date entered in dd/MM/yyyy format.
Dim isValid As Boolean = regex.IsMatch(txtDate.Text.Trim)
'Verify whether entered date is Valid date.
Dim dt As DateTime
isValid = DateTime.TryParseExact(txtDate.Text, "dd/MM/yyyy", New CultureInfo("en-GB"), DateTimeStyles.None, dt)
If Not isValid Then
MessageBox.Show("Invalid Date.")
End If
End Sub
Screenshot
![Date format (dd/MM/yyyy) validation using Regular Expression in C# and VB.Net]()
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