Categories
asp.net validation

How does Page.IsValid work?

I have following code with a RequiredFieldValidator. The EnableClientScript property is set as “false” in the validation control. Also I have disabled script in browser.

I am NOT using Page.IsValid in the code behind. Still, when I submit without any value in textbox I will get error message.

From comments of @Dai, I came to know that this can be an issue, if there is any code in Page_Load that is executed in a postback. There will be no validation errors thrown.

(However, for button click handler, there is no need to check Page.IsValid)

if (Page.IsPostBack)
{
string value = txtEmpName.Text;
txtEmpName.Text = value + "Appended";
}

QUESTION

  1. Why does not the server side validation happen before Page_Load?
  2. Why does it work fine when I use Page.IsValid?
  3. Can you provide any reference to an article that explains this? (Not something that says – always use Page.IsValid; but something that says what are the mandatory scenarios to use Page.IsValid

UPDATE 1

Refer ASP.NET Validators Common Misconception

Page.IsValid is accessible only after running Page.Validate() method which is invoked implicitly somewhere after Page_Load. In case you keep all of your logic in a Page_Load event handler (which is highly discouraged!), call the Page.Validate() before checking the Page.IsValid.

Note: It is advised not to keep all the logic in Page_Load. If something is to happen on button click event, move it to button click event handler. If something is to happen on drop-down event, move it to drop-down selected item change event handler.

UPDATE 2

It seems like, we need to add If(Page.IsValid) in button click also if we are using a Custom Validator with server side validation. Refer CustomValidator not working well.

Note: Client side validation question is present here: Whether to use Page_IsValid or Page_ClientValidate() (for Client Side Events)

MARKUP

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<script type="text/javascript">
alert('haiii');
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:ValidationSummary runat="server" ID="vsumAll" DisplayMode="BulletList" CssClass="validationsummary" ValidationGroup="ButtonClick" />
<asp:TextBox ID="txtEmpName" runat="server"></asp:TextBox>
<asp:RequiredFieldValidator ID="valEmpName" runat="server" ControlToValidate="txtEmpName"
EnableClientScript="false" ErrorMessage="RequiredFieldValidator" Text="*" Display="Dynamic"
ValidationGroup="ButtonClick"></asp:RequiredFieldValidator>
<asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" ValidationGroup="ButtonClick" />
</div>
</form>
</body>
</html>

CODE BEHIND

protected void Button1_Click(object sender, EventArgs e)
{
string value = txtEmpName.Text;
SubmitEmployee(value);
}

References:

  1. Should I always call Page.IsValid?
  2. ASP.NET Validation Controls – Important Points, Tips and Tricks
  3. CustomValidator not working well