ASP.NET CheckBoxList Client Side Validation using JavaScript

Introduction

In this blog, we will explore a trick to validate whether any CheckBox inside one CheckBoxList is checked or not.

Problem

When you define one CheckBoxList on aspx page by writing code something like below…

<asp:CheckBoxList RepeatDirection="Horizontal" 
                  ID="chkDemo"
                  runat="server">
    <asp:ListItem Text="Apples" Value="1"></asp:ListItem>
    <asp:ListItem Text="Oranges" Value="2"></asp:ListItem>
    <asp:ListItem Text="Mangoes" Value="3"></asp:ListItem>
</asp:CheckBoxList>

...it will render on browser like below…

<table id="chkDemo">
    <tbody>
        <tr>
            <td>
                <input type="checkbox" value="1" name="chkDemo$0" id="chkDemo_0">
                <label for="chkDemo_0">Apples</label>
            </td>
            <td>
                <input type="checkbox" value="2" name="chkDemo$1" id="chkDemo_1">
                <label for="chkDemo_1">Oranges</label>
            </td>
            <td>
                <input type="checkbox" value="3" name="chkDemo$2" id="chkDemo_2">
                <label for="chkDemo_2">Mangoes</label>
            </td>
        </tr>
    </tbody>
</table>

Basically, it renders number of CheckBoxes depending on the number of ListItems inside CheckBoxList.

So, What Is the Logic Here?

We will call one JavaScript function on a Button Click.
Button would look like…

<asp:Button runat="server" ID="Button1" Text="Submit" 
            OnClientClick="return validateCheckBoxList();" />

Inside that function, we will run the following logic to validate whether any CheckBox is checked or not.

1. We will find the main CheckBoxList first, which is rendered as a Table.
2. Next, we need to find all the CheckBoxes inside that Table.
3. After that, we have to check if any CheckBox is checked by looping through them.
4. If any CheckBox is checked, then break the Loop and show alert (for demo purpose).
5. Return true if any CheckBox is checked, else show alert and return false.

function validateCheckBoxList() {
    var isAnyCheckBoxChecked = false;

    // ::: Step-1 & 2 ::: Let's get all the CheckBoxes inside the CheckBoxList.
    var checkBoxes = document.getElementById("chkDemo").getElementsByTagName("input");
    
    // ::: NOTE ::: For jsfiddle demo I have directly used the ID. 
    // Otherwise you might have to use ClientID like below...
    // document.getElementById
    // ("<%= chkDemo.ClientID %>").getElementsByTagName("input");

    // ::: Step-3 ::: Now let's Loop through the Children.
    for (var i = 0; i < checkBoxes.length; i++) {
        if (checkBoxes[i].type == "checkbox") {
            if (checkBoxes[i].checked) {
                // ::: Step-4 ::: If current CheckBox is checked, then show alert.
                // Break the Loop.
                isAnyCheckBoxChecked = true;
                alert("Atleast one CheckBox is checked");
                break;
            }
        }
    }
 
    // ::: Step-5 ::: Check if any CheckBox is checked or not.
    // Show alert and return accordingly.
    if (!isAnyCheckBoxChecked) {
        alert("No CheckBox is Checked.");
    }

    return isAnyCheckBoxChecked;
}

See the Demo

Here

Note

I have used the CheckBoxList ID directly, which is chkDemo. But when your ClientID changes, you can get the CheckBoxList like…

document.getElementById("<%= chkDemo.ClientID %>");

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