如何确定JavaScript中RadioButtonList的SelectedValue？

Question

I have an ASP.NET web page with a databound RadioButtonList. I do not know how many radio buttons will be rendered at design time. I need to determine the SelectedValue on the client via JavaScript. I've tried the following without much luck:

var reasonCode = document.getElementById("RadioButtonList1");
var answer = reasonCode.SelectedValue;  

("answer" is being returned as "undefined") Please forgive my JavaScript ignorance, but what am I doing wrong?

Thanks in advance.

Answer 1

ASP.NET renders a table and a bunch of other mark-up around the actual radio inputs. The following should work:-

 var list = document.getElementById("radios"); //Client ID of the radiolist
 var inputs = list.getElementsByTagName("input");
 var selected;
 for (var i = 0; i < inputs.length; i++) {
      if (inputs[i].checked) {
          selected = inputs[i];
          break;
       }
  }
  if (selected) {
       alert(selected.value);
  }

Answer 2

尝试此操作以从RadioButtonList中获取选定的值。

var selectedvalue = $('#<%= yourRadioButtonList.ClientID %> input:checked').val()

Answer 3

I always View Source. You will find each radio button item to have a unique id you can work with and iterate through them to figure out which one is Checked.

Edit: found an example. I have a radio button list rbSearch. This is in an ascx called ReportFilter. In View Source I see

ReportFilter1_rbSearch_0
ReportFilter1_rbSearch_1
ReportFilter1_rbSearch_2

So you can either loop through document.getElementById("ReportFilter1_rbSearch_" + idx ) or have a switch statement, and see which one has .checked = true.

Answer 4

I would like to add the most straightforward solution to this problem:

var reasons= document.getElementsByName("<%=RadioButtonList1.UniqueID%>");
var answer;
for (var j = 0; j < reasons.length; j++) {
    if (reason[j].checked) {
        answer = reason[j].value;
    }
}

UniqueID is the property that gave you the name of the inputs inside the control, so you can just check them really easily.

Answer 5

For a 'RadioButtonList with only 2 values 'yes' and 'no', I have done this:

var chkval=document.getElemenById("rdnPosition_0")

Here rdnposition_0 refers to the id of the yes ListItem . I got it by viewing the source code of the form.

Then I did chkval.checked to know if the value 'Yes' is checked.

Answer 6

RadioButtonList is an ASP.NET server control. This renders HTML to the browser that includes the radio button you are trying to manipulate using JavaScript.

I'd recommend using something like the IE Developer Toolbar (if you prefer Internet Explorer) or Firebug (if you prefer FireFox) to inspect the HTML output and find the ID of the radio button you want to manipulate in JavaScript.

Then you can use document.getElementByID("radioButtonID").checked from JavaScript to find out whether the radio button is selected or not.

Answer 7

The HTML equivalent to ASP.NET RadioButtonList, is a set of <input type="radio"> with the same name attribute(based on ID property of the RadioButtonList).

You can access this group of radio buttons using getElementsByName. This is a collection of radio buttons, accessed through their index.

alert( document.getElementsByName('RadioButtonList1') [0].checked );

Answer 8

function CheckRadioListSelectedItem(name) {

    var radioButtons = document.getElementsByName(name);
    var Cells = radioButtons[0].cells.length;

    for (var x = 0; x < Cells; x++) {
        if (document.getElementsByName(name + '_' + x)[0].checked) {
            return x;
        }
    }

    return -1;
}

Answer 9

I've tried various ways of determining a RadioButtonList's SelectedValue in Javascript with no joy. Then I looked at the web page's HTML and realised that ASP.NET renders a RadioButtonList control to a web page as a single-column HTML table!

<table id="rdolst" border="0">
  <tr>
    <td><input id="rdolst_0" type="radio" name="rdolst" value="Option 1" /><label for="rdolst_0">Option 1</label></td>
  </tr>
  <tr>
    <td><input id="rdolst_1" type="radio" name="rdolst" value="Option 2" /><label for="rdolst_1">Option 2</label></td>
  </tr>
</table>

To access an individual ListItem on the RadioButtonList through Javascript, you need to reference it within the cell's child controls (known as nodes in Javascript) on the relevant row. Each ListItem is rendered as the first (zero) element in the first (zero) cell on its row.

This example loops through the RadioButtonList to display the SelectedValue:

var pos, rdolst;

for (pos = 0; pos < rdolst.rows.length; pos++) {
    if (rdolst.rows[pos].cells[0].childNodes[0].checked) {
        alert(rdolst.rows[pos].cells[0].childNodes[0].value);
        //^ Returns value of selected RadioButton
    }
}

To select the last item in the RadioButtonList, you would do this:

rdolst.rows[rdolst.rows.length - 1].cells[0].childNodes[0].checked = true;

So interacting with a RadioButtonList in Javascript is very much like working with a regular table. Like I say I've tried most of the other solutions out there but this is the only one which works for me.

Answer 10

I wanted to execute the ShowShouldWait script only if the Page_ClientValidate was true . At the end of the script, the value of b is returned to prevent the postback event in the case it is not valid.

In case anyone is curious, the ShouldShowWait call is used to only show the "please wait" div if the output type selected is "HTML" and not "CSV".

onclientclick="var isGood = Page_ClientValidate('vgTrxByCustomerNumber');if(isGood){ShouldShowWait('optTrxByCustomer');} return isGood"

Answer 11

To check the selected index of drop down in JavaScript:

function SaveQuestion() {
    var ddlQues = document.getElementById("<%= ddlQuestion.ClientID %>");
    var ddlSubQues = document.getElementById("<%=ddlSecondaryQuestion.ClientID%>");

    if (ddlQues.value != "" && ddlSubQues.value != "") {
        if (ddlQues.options[ddlQues.selectedIndex].index != 0 ||
            ddlSubQues.options[ddlSubQues.selectedIndex].index != 0) {
            return true;
        } else {
            return false;
        }
    } else {
        alert("Please select the Question or Sub Question.");
        return false;
    }
}

Answer 12

reasonCode.options[reasonCode.selectedIndex].value

Answer 13

From here :

if (RadioButtonList1.SelectedIndex > -1) 
{
    Label1.Text = "You selected: " + RadioButtonList1.SelectedItem.Text;
}