CODEWITHSUNDEEP
asp.netvalidationlistboxcustomvalidator
chris
chris

Reputation:

How do I validate that a list box is not empty (client side)

I'm working with ASP.NET 3.5. I have a list box that users must add items to (I've written the code for this). My requirement is that at least one item must be added to the listbox or they cannot submit the form. I have several other validators on the page and they all write to a ValidationSummary control. I would like this listbox validation to write to the Validation Summary control as well. Any help is greatly appreciated. Thank you.

Upvotes: 3

Views: 20945

Answers (7)

Zack Rose
Zack Rose

Reputation: 11

Actually this is the proper way to make this work (as far as the JavaScript is concerned).

ListBox.options.length will always be your total number of options, not the number you have selected. The only way I have found that works is to use a for loop to go through the list.

function ListBoxValid(sender, args)
{

    var listBox = document.getElementById(sender.controltovalidate);

    var listBoxCnt = 0;

    for (var x =0; x<listBox.options.length; x++)
    {
        if (listBox.options[x].selected) listBoxCnt++;
    }

    args.IsValid = (listBoxCnt>0)

}

Upvotes: 1

Summao
Summao

Reputation: 1

this work for me

<script language="JavaScript">
  function CheckListBox(sender, args)
  {
      args.IsValid = document.getElementById("<%=ListBox1.ClientID%>").options.length > 0;
  }
</script>    
<asp:ListBox ID="ListBox1" runat="server"></asp:ListBox>
<asp:CustomValidator ID="CustomValidator1" runat="server" 
ErrorMessage="*Required" ClientValidationFunction="CheckListBox"></asp:CustomValidator>

Upvotes: 0

Tiago
Tiago

Reputation: 31

gotta make sure to add these properties to the CustomValidator:

Display="Dynamic" ValidateEmptyText="True"

Upvotes: 3

Naeem Sarfraz
Naeem Sarfraz

Reputation: 7430

This didn't work for me:

function ListBoxValid(sender, args) 
{
        args.IsValid = sender.options.length > 0; 
}

But this did:

function ListBoxValid(sender, args)
{
        var ctlDropDown = document.getElementById(sender.controltovalidate);
        args.IsValid = ctlDropDown.options.length > 0; 
}

Upvotes: 5

FlySwat
FlySwat

Reputation: 175733

<asp:CustomValidator 
     runat="server" 
     ControlToValidate="listbox1"
     ErrorMessage="Add some items yo!" 
     ClientValidationFunction="checkListBox"
/>

<script type="Text/JavaScript">
  function checkListBox(sender, args)
  {
      args.IsValid = sender.options.length > 0;
  }
</script>

Upvotes: 1

stephenbayer
stephenbayer

Reputation: 12431

Drop in a custom validator, Add your desired error message to it, double click on the custom validator to get to the code behind for the event handler, and then you would implement server side like this:

protected void CustomValidator1_ServerValidate(object source, ServerValidateEventArgs args) 
{
        args.IsValid = ListBox1.Items.Count > 0; 
}

Also you can implement client side javascript as well.

I just threw this up on a page and tested it quickly, so you might need to tweak it a bit: (The button1 only adds an item to the List Box)

<script language="JavaScript">
<!--
  function ListBoxValid(sender, args)
  {
      args.IsValid = sender.options.length > 0;
  }
// -->
</script>    
<asp:ListBox ID="ListBox1" runat="server"></asp:ListBox>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" ValidationGroup="NOVALID" />
<asp:Button ID="Button2" runat="server" Text="ButtonsUBMIT"  />

<asp:CustomValidator ID="CustomValidator1" runat="server" 
ErrorMessage="CustomValidator" 
onservervalidate="CustomValidator1_ServerValidate" ClientValidationFunction="ListBoxValid"></asp:CustomValidator>

If you add a validation summary to the page, you error text should show up in that summary if there is no items in the ListBox, or other collection-able control, what ever you want to use, as long as the ValidationGroup is the same.

Upvotes: 5

Jason N. Gaylord
Jason N. Gaylord

Reputation: 8334

You will want to register your control with the page by sending in the ClientID. Then, you can use Microsoft AJAX to grab your control and check the values.

Upvotes: -1

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