textbox validation in asp.net

You can take the help of RequiredFieldValidater validation control for checking blank textbox(textbox should not be blank).

<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:RequiredFieldValidator ID="RequiredFieldValidator1"runat="server" ControlToValidate="TextBox1" Display="Dynamic" ErrorMessage="should not be blank !!"></asp:RequiredFieldValidator>

with events you should set AutoPostBack to True then use this event :

protected void btnSubmitForm_Click(object sender, EventArgs e)
{
   if(textbox1.Text=="")
  {
    //do anything you want
  }
}

then check if it is blank ...


you can use this too :

<asp:requiredfieldvalidator id="RequiredFieldValidator1" runat="server" controltovalidate="txtName" xmlns:asp="#unknown">
ErrorMessage="Enter your name!" 
ForeColor="Red">
</asp:requiredfieldvalidator>

you can use javascript on onblur event to validate textbox on 'ontextchanged' event
for details use following link:
textbox focus out validation using custom validator[^]

Generally your required field validator will take care of that. But in case if you want serverside validation for that, then try this:

if(textbox1.Text.Trim() != ""){
    //Show error message
}
else{
   //Success.
}

--Amit