Input string was not in a correct format and Requiredfieldvalidator not working properly

Question

So with the suggestions i updated my code.

Textbox:

 <asp:TextBox ID="txtStudent_Id" runat="server"></asp:TextBox></td>

 <asp:RequiredFieldValidator runat="server" 
  ControlToValidate="txtStudent_Id"
  ErrorMessage="Id is required"
  ID="validator_ID"
  ValidationGroup="Validation_ID">
  </asp:RequiredFieldValidator>

        <asp:RegularExpressionValidator id="RegularExpressionValidator1"
          ControlToValidate="txtStudent_Id"
          ValidationExpression="\d+"
          Display="Static"
          EnableClientScript="true"
          ErrorMessage="Please enter numbers only" ValidationGroup="Validation_ID"
          runat="server"/>

Button:

<asp:Button runat="server" Text="Submit" ID="btnSubmitStudent" ValidationGroup="Validation_ID" CausesValidation="true" OnClick="btnSubmitStudent_Click" />

Code Behind:

addstudent.Student_Id =Convert.ToInt32(txtStudent_Id.Text);

Now that i have also entered the regular expression validator it should work but i still get the same error.

Answer 1

TextBox

<asp:TextBox ID="txtStudent_Id"
             runat="server"
             ValidationGroup="VAlidation_Name">
</asp:TextBox>

RequiredFieldValidator

you have not added id to the RequiredFieldValidator and also ValidationGroup

<asp:RequiredFieldValidator runat="server"  
                            Display="Dynamic" 
                            ControlToValidate="txtStudent_Id"
                            ID="rfvStudent_Id"
                            ForeColor="Red"
                            ValidationGroup="VAlidation_Name"
                            ErrorMessage="Id is required">
</asp:RequiredFieldValidator>

Button Submit

<asp:Button ID="btnSubmit" Text="Submit"
            runat="server"
            ValidationGroup="VAlidation_Name" CausesValidation="true" />

In default CausesValidation="true" but check that too.

Code Part

addstudent.Student_Id =int.TryParse(txtStudent_Id.Text);

Suggestion:

And you can use AjaxToolKit Extender MaskedEdit to make the user enter only integer.

<asp:MaskedEditExtender ID="txtEndDate_MaskedEditExtender" runat="server" ClearTextOnInvalid="True"
                            ClearMaskOnLostFocus="true"  Enabled="True" Mask="9999999"
                            MaskType="Date" TargetControlID="txtStudent_Id"
                             ErrorTooltipEnabled="True"> 

Updated:

void SubmitButton_Click(object sender, EventArgs e)
{
    if (!Page.IsValid)
        return;

    // Do form stuff
}

Check this too EnableClientScript="True" and Enabled="True"

 <asp:RequiredFieldValidator runat="server"  
                                Display="Dynamic" 
                                ControlToValidate="txtStudent_Id"
                                ID="rfvStudent_Id"
                                EnableClientScript="True"
                                Enabled="True"
                                ForeColor="Red"
                                ValidationGroup="VAlidation_Name"
                                ErrorMessage="Id is required">
    </asp:RequiredFieldValidator>

Answer 2

Don't need a solution for your error.need a solution why the validation control not works? and how can solve this problem?then what i do?

Main thing

You have missed ValidationGroup="XXXXX" in validation control and button control, So it's allowed to server side code, so first add that and

try with this asp:RegularExpressionValidator for only allow integer value, So It's not allow if you type any special and string characters

<asp:TextBox ID="txtStudent_Id" runat="server"></asp:TextBox>
<asp:RequiredFieldValidator runat="server" 
     ControlToValidate="txtStudent_Id" ValidationGroup="XXXXX"    EnableClientScript="True"
     ErrorMessage="Id is required">
 </asp:RequiredFieldValidator>

<asp:RegularExpressionValidator id="RegularExpressionValidator1"
                   ControlToValidate="txtStudent_Id"
                   ValidationExpression="\d+"
                   Display="Static"
                   EnableClientScript="true"
                   ErrorMessage="Please enter numbers only" ValidationGroup="XXXXX"
                   runat="server"/>

<asp:button ValidationGroup="XXXXX"></asp:button>

or

 <asp:button ValidationGroup="XXXXX" CasusesValidation="true"></asp:button>

If you try my answer,then don't worry about Input string was not in a correct format. error.

Update:

please try this in your button click event.

Page.Validate();

if (Page.IsValid == false)
{

return;
}

//Call your code here