RequiredFieldValidator in ASP.Net with Set focus on error

The RequiredFieldValidator is used to ensure that the user has entered the data into input control. The RequiredFieldValidator control belongs to


System.Web.UI.WebControls

1. For Text Box

1. <RequiredFieldValidator  
2. id="reqFirstName" ControlToValidate="TextBox1" Text="(Required)"  
3. SetFocusOnError="true" Runat="server" ValidationGroup="f1"></asp:RequiredFieldValidator>  

Property	Description
ControlToValidate	Specifies control name which needs to be validate.
Display	Specifies behavior of the error message.
EnableClientScript	Specifies whether or not client-side validation is enabled.
Enabled	Specifies whether or not validation control is enabled or not.
ErrorMessage	Specifies error messageto be display in validation summary.
ForeColor	Specifies error message color.
IsValid	Indicate if associate control passes validation or not.
SetFocusOnError	Set focus on associate control if validation fails.
Text	Specifies text to be display if validation fails.
ValidationGroup	Specifies validation group name.
Validate	Update the isvalid propery.
ValidateGetValidationProperty	Determineing validation property of a control, if it exists.

RequiredFieldValidator

Specifies initial value of input control.

2. For Dropdown List

1. <RequiredFieldValidator  
2. id="reqFirstName" ControlToValidate="TextBox1" Text="(Required)"  
3. SetFocusOnError="true" Runat="server" InitialValue="--Select Service--"  ValidationGroup="f1"></asp:RequiredFieldValidator>  

3. For email address validation

1. <asp:TextBox ID="txtEmailAddress" runat="server"  placeholder="Email here..." type="email" class="form-control"></asp:TextBox> 
2. <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ErrorMessage="Enter Email/ Username" ControlToValidate="txtEmailAddress" ValidationGroup="v1" ForeColor="#cc0000" SetFocusOnError="true"></asp:RequiredFieldValidator>
3. <asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ControlToValidate="txtEmailAddress" ForeColor="Red" ValidationExpression="^([\w-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([\w-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$"  ErrorMessage = "Invalid email address" ValidationGroup="v1" SetFocusOnError="true"/>

Here there is two control one is RequiredFieldValidator which validate empty field and another is RegularExpressionValidator which validate email address. I have use here one regular express which validate any email address.