How to allow maximum check box to check in a checkboxlist in asp.net c#

Question

I have a checkboxList having some items.I want to specify a maximum checkbox to allow checking How can we do this using c# code.

here is my code

<asp:CheckBoxList ID="chkLstFields" runat="server" AutoPostBack="true">

                                            </asp:CheckBoxList>


int br_id = Convert.ToInt32(ddlBrand.SelectedValue);
        int status = Convert.ToInt32(ddlStatus.SelectedIndex.ToString());
        DataTable dt_Spec = bl.sp_select_model_spec_field(br_id, status);
        chkLstFields.Items.Clear();

        if (dt_Spec.Rows.Count > 0)
        {
            for (int i = 0; dt_Spec.Rows.Count > i; i++)
            {
                chkLstFields.Items.Add(dt_Spec.Rows[i].ItemArray[0].ToString());

            }
        }

The question is unclear. Where in your code are you trying to specify a "maximum checkbox"(whatever that is)? — Tim Schmelter
– Tim Schmelter, Commented Jan 9, 2015 at 9:29
Do you mean you have N checkboxes and you want to only allow the user to check N-M checkboxes, where you want to specify M in code? I'd check this serverside and clientside, for the latter you'll need JavaScript. — CodeCaster
– CodeCaster, Commented Jan 9, 2015 at 9:30

Tim Schmelter · Accepted Answer · 2015-01-09 09:44:00Z

You could use a CustomValidator for this purpose. I've realized it in an old VB.NET project.

Here is the relevant aspx:

<asp:ListBox ID="LbSymptomCodesInsert" runat="server" 
    CausesValidation="true" 
    ValidationGroup="VG_RMA_SAVE" SelectionMode="Multiple"> 
</asp:ListBox>
<asp:CustomValidator ID="CV_SymptomCodeSelectionCount" runat="server" 
    ValidateEmptyText="true" 
    ClientValidationFunction="validateSymptomCodeSelectionCount" 
    OnServerValidate="validateSymptomCodeSelectionCount" 
    ControlToValidate="LbSymptomCodesInsert" 
    Display="None" 
    EnableClientScript="true" 
    ErrorMessage="Select at least one and at most 5 SymptomCodes" 
    Style="visibility: hidden" 
    ValidationGroup="VG_RMA_SAVE">*</asp:CustomValidator>

Here are the javascript functions:

function validateSymptomCodeSelectionCount(sender, args){
    var listbox = document.getElementById('LbSymptomCodesInsert');
    args.IsValid = validateListBoxSelectionCount(listbox, 1, 5);
}

function validateListBoxSelectionCount(listbox, minSelected, maxSelected){
    var selected=0;
    if(listbox != null){
        for (var i=0; i<listbox.length; i++){
            if(listbox.options[i].selected){
               selected++; 
               if(selected>maxSelected)break;
            }
        }
    }
   return (selected >= minSelected && selected <= maxSelected);
}

Here's the ServerValidate (VB.NET but i'm sure you get the point):

Protected Sub validateSymptomCodeSelectionCount(ByVal source As Object, ByVal args As ServerValidateEventArgs)
    Dim count = 0
    For Each item As ListItem In LbSymptomCodesInsert.Items
        If item.Selected Then count += 1
        If count > 5 Then Exit For
    Next
    args.IsValid = (count >= 1 AndAlso count <= 5)
End Sub

Ehsan Sajjad · Accepted Answer · 2015-01-09 09:33:20Z

1

If you want to limit the number of items checked,you can limit the checked items amount this way:

if(chkLstFields.Items.OfType<ListItem>().Count(x => x.Selected) > 2)
{

  // show message you cannot select more than 2 items
}
else
{
 // continue execution
}

answered Jan 9, 2015 at 9:33

Ehsan Sajjad

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