ASP.NET Validations Tips and Tricks Part-I

Introduction

Validation controls are used to validate the ASP.NET input server controls like asp:TextBox for valid data when their data is submitted to the server. There are six validation controls in ASP.NET and they are

1. RequiredFieldValidator

2. RangeValidator

3. CompareValidator

4. RegularExpressionValidator

5. CustomValidator and

6. ValidationSummary

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Now, let's learn some Tips and Tricks related with Validation controls.

How to validate a TextBox as a mandatory field?

To make a TextBox mandatory for the end user to enter before a form can be submitted to the server, we can follow this approach.

ASPX PAGE

 
Username:<asp:TextBox ID="txtUserName" runat="server" />
       <asp:RequiredFieldValidator ID="req1" runat="server" ErrorMessage="Mandatory !" ForeColor="Red"ControlToValidate="txtUserName" />
       <p><asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="SubmitData" /></p>

CODE BEHIND

protected void SubmitData(object sender, EventArgs e)
{

}

In the above code snippet, we have a TextBox and a Button. As we want to validate the textbox as a mandatory field so we have used asp:RequiredFieldValidator with ErrorMessage that we want to display if the validation fails and ControlToValidate property set to the TextBox (in this case the textbox id is txtUserName) that should be validated.

OUTPUT

How to validate a DropDownList / ListBox?

To validate a DropDownList or ListBox as a mandatory field so that user has to select any item from them apart from pre-selected item, we can follow this approach.

ASPX PAGE

Select age: <asp:DropDownList ID="dropDownAge" runat="server">
            <asp:ListItem Text="Select Age" Value="0" />
            <asp:ListItem Text="18" Value="18" />
            <asp:ListItem Text="19" Value="19" />
            <asp:ListItem Text="20" Value="20" />
            <asp:ListItem Text="> 20" Value=">20" />
        </asp:DropDownList>
        <asp:RequiredFieldValidator ID="reqAge" runat="server" ErrorMessage="Please
select age" ForeColor="Red" ControlToValidate="dropDownAge" InitialValue="0" />
<p><asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="SubmitData" /></p>

CODE BEHIND

protected void SubmitData(object sender, EventArgs e)
{

}

In the above code snippet, the first item of the DropDownList is “Select Age” with value as “0”; we want the user to select any age. To do that we can specify the RequiredFieldValidator's InitialValue as “0”, this will cause the RequiredFieldValidator fail unless user select any age other than “0” from the DropDownList.

OUTPUT

Note: Similarly we can perform ListBox validation too.

What is CauseValidation property and how to avoid validation on clicking of a button?

In case we have multiple buttons on the page and we want to avoid validation on clicking of certain button, we can use this approach.

ASPX PAGE

<p>
Username: <asp:TextBox ID="txtUserName" runat="server" />
<asp:RequiredFieldValidator ID="req1" runat="server" ErrorMessage="Mandatory !" 
ForeColor="Red"ControlToValidate="txtUserName" />
        </p>
        <p>
Password: <asp:TextBox ID="txtPassword" runat="server" TextMode="Password" />
<asp:RequiredFieldValidator ID="req2" runat="server" ErrorMessage="Mandatory !" 
ForeColor="Red"ControlToValidate="txtPassword" />
</p>
<asp:Button ID="btnSubmit" runat="server" Text="Login" OnClick="SubmitData" />
 
 <asp:Button ID="Button1" runat="server" Text="Do something else"
 CausesValidation="false"OnClick="DoSomethingElse" />

CODE BEHIND

protected void SubmitData(object sender, EventArgs e)
{
}

protected void DoSomethingElse(object sender, EventArgs e)
{
}
 

In the above code snippet, on .aspx page we have Username and Password two textboxes. We have placed RequiredFieldValidator for both of them. Clicking “Login” button causes validation on both TextBoxes but clicking on “Do something else” button doesn't cause form validations because its CauseValidation property is set to false.

OUTPUT

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