Allow only Lowercase characters in Windows Form TextBox using C# and VB.Net

Hi rani,

Refer below sample. This will check and display message box.

Code

C#

private void txtName_KeyUp(object sender, KeyEventArgs e)
{
    if (txtName.Text.Any(char.IsUpper))
    {
        MessageBox.Show("Please Enter Characters in lowercase!");
        txtName.Clear();
    }     
}

VB.Net

Private Sub txtName_KeyUp(sender As System.Object, e As System.Windows.Forms.MouseEventArgs) Handles txtName.MouseUp
    If txtName.Text.Any(AddressOf Char.IsUpper) Then
        MessageBox.Show("Please Enter Characters in lowercase!")
        txtName.Clear()
    End If
End Sub

Screenshot

OR

You can also use below line of code to allow only lowercase characters for type.

C#

txtName.CharacterCasing = CharacterCasing.Lower;

VB.Net

txtName.CharacterCasing = CharacterCasing.Lower