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 User Input Validation - Client & Server - in C#.NET

This tutorial shows how you can validate the input of users using ASP.NET and C# This tutorial shows how the ASP.NET tools make it easy for you to validate user input, both client-side and server-side.

First we add the form elements from the Toolbox, including the RequiredFieldValidator, RegularExpressionValidator and the ValidationSummary.

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Note the CustomValidator control, which allows us to create a custom rule for validation. This particular one checks to see if a date is in the correct format:

<form id="form1" runat="server">
<div>
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="textEmail" Display="Dynamic" ErrorMessage="Email Address is Required" ValidationGroup="AllValidators">*</asp:RequiredFieldValidator>
Email:
<asp:TextBox ID="textEmail" runat="server"></asp:TextBox> 
<asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ControlToValidate="textEmail" Display="Dynamic" ErrorMessage="Email Address must be in the format abc@xyz.abc" ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*" ValidationGroup="AllValidators">Invalid Format</asp:RegularExpressionValidator><br />

<asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ControlToValidate="textNumberInParty" ErrorMessage="Number in Party is Required" ValidationGroup="AllValidators">*</asp:RequiredFieldValidator>
Number in Party:
<asp:TextBox ID="textNumberInParty" runat="server" Width="45px"></asp:TextBox> 
<asp:RangeValidator ID="RangeValidator1" runat="server" ControlToValidate="textNumberInParty" Display="Dynamic" ErrorMessage="Please enter 1-20 for the number of people in your party" MaximumValue="20" MinimumValue="1" Type="Integer" ValidationGroup="AllValidators">Enter a number between 1 and 20</asp:RangeValidator><br />

<asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" ControlToValidate="textPreferredDate" Display="Dynamic" ErrorMessage="Date is Required" ValidationGroup="AllValidators">*</asp:RequiredFieldValidator>
Preferred Date:
<asp:TextBox ID="textPreferredDate" runat="server"></asp:TextBox>
<asp:CustomValidator ID="CustomValidator1" runat="server" ControlToValidate="textPreferredDate" Display="Dynamic" ErrorMessage="Format: m/d/yyyy" OnServerValidate="CustomValidator1_ServerValidate" ValidationGroup="AllValidators" ClientValidationFunction="validateDate">Invalid format (m/d/yyyy)</asp:CustomValidator><br />

<asp:RequiredFieldValidator ID="validatorRequiredPhoneNumber" runat="server" ControlToValidate="textPhoneNumber" Display="Dynamic" ErrorMessage="You must provide a phone number">*</asp:RequiredFieldValidator>
<asp:CheckBox ID="checkPhoneConfirmation" runat="server" AutoPostBack="True" OnCheckedChanged="checkPhoneConfirmation_CheckedChanged" Text="Confirm Reservation by Phone" /><br />
Tel. No.
<asp:TextBox ID="textPhoneNumber" runat="server" Enabled="False"></asp:TextBox> 
<asp:RegularExpressionValidator ID="validatorRegExPhoneNumber" runat="server" ControlToValidate="textPhoneNumber" Display="Dynamic" ErrorMessage="Phone number format is invalid" ValidationExpression="((\(\d{3}\) ?)|(\d{3}-))?\d{3}-\d{4}">Invalid Format</asp:RegularExpressionValidator><br />
<asp:Button ID="buttonSubmit" runat="server" OnClick="buttonSubmit_Click" Text="Submit" ValidationGroup="AllValidators" /><br />
<asp:Label ID="labelResponse" runat="server"></asp:Label><br />
<asp:ValidationSummary ID="ValidationSummary1" runat="server" ValidationGroup="AllValidators" />
</div>
</form>

In the code-behind file we have the following:

protected void Page_Load(object sender, EventArgs e)
{
labelResponse.Text = "";
}
protected void buttonSubmit_Click(object sender, EventArgs e)
{
if (Page.IsValid)
{
labelResponse.Text = "Your request has been processed. Thank you.";
}
else
{
labelResponse.Text = "Date is not valid.";
}
}
protected void CustomValidator1_ServerValidate(object source, ServerValidateEventArgs args)
{
try
{
DateTime.ParseExact(args.Value, "d", null);
args.IsValid = true;
}
catch
{
args.IsValid = false;
}
} protected void checkPhoneConfirmation_CheckedChanged(object sender, EventArgs e)
{
if(checkPhoneConfirmation.Checked)
{
textPhoneNumber.Enabled = true;
validatorRequiredPhoneNumber.ValidationGroup = "AllValidators";
validatorRegExPhoneNumber.ValidationGroup = "AllValidators";
}
else
{
textPhoneNumber.Enabled = false;
validatorRequiredPhoneNumber.ValidationGroup = "";
validatorRegExPhoneNumber.ValidationGroup = "";
}
}

For client-side validation of the date field, we can use a bit of JavaScript:

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Note: For this to work, the 'EnableClientScript' Property of the CustomValidator has to be set to True.

<script language="javascript">
function validateDate(oSrc, args)
{
var iDay, iMonth, iYear;
var arrValues;
arrValues = args.Value.split("/");
iMonth = arrValues[0];
iDay = arrValues[1];
iYear = arrValues[2];

var testDate = new Date(iYear, iMonth - 1, iDay);
if ((testDate.getDate() != iDay) ||
(testDate.getMonth() != iMonth - 1) ||
(testDate.getFullYear() != iYear))
{
args.IsValid = false;
return;
}

return true;
} </script>


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