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How to get JavaScript variable value in C# code behind

I have a gridview with a column with customised button.
When I click the button, user contact is asked for through JavaScript and then the contact is passed on to rowCommand event of gridview for some operation.
I am using Hiddenfield as a gridview column but there is something going wrong in setting and getting the value.
JavaScript code:
<script type="text/javascript">
function validateContact()
{
var contact = prompt("Please enter your contact number.");
if (isEmpty(contact) && !isNumber(contact) && contact.length != 10)
alert("Invalid contact.");
return;
else
document.getElementById("hiddenCustomerContact.ClientID").value = contact;
}
</script>
asp code:
<asp:GridView ID="gridSearchWorker" runat="server" AutoGenerateColumns="false" OnRowCommand="gridSearchWorker_OnRowCommand" OnRowDataBound="gridSearchWorker_RowDataBound">
<Columns>
<asp:BoundField DataField="WORKER" HeaderText="WORKER" SortExpression="WORKER">
<ItemStyle Width="12%" />
</asp:BoundField>
<asp:TemplateField HeaderText = "" ItemStyle-Width="5%">
<ItemTemplate>
<asp:Button ID="btnGetContact" runat="server" Text="Get Contact" CommandName="GetContact" OnClientClick="validateContact();" />
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="CONTACT" HeaderText="CONTACT" SortExpression="CONTACT">
<ItemStyle Width="12%" />
</asp:BoundField>
<asp:TemplateField HeaderText = "" ItemStyle-Width="5%">
<ItemTemplate>
<asp:HiddenField ID="hiddenCustomerContact" runat="server"/>
</ItemTemplate>
<ItemStyle Width="0.0001%" />
</asp:TemplateField>
</Columns>
</asp:GridView>
c# code behind:
protected void gridSearchWorker_OnRowCommand(object sender, GridViewCommandEventArgs e)
{
if (e.CommandName == "GetContact")
{
OleDbConnection conn = new OleDbConnection(cs);
//ask for contact and check if any feedback pending
HiddenField hiddenCustomerContact =
e.Row.FindControl("hiddenCustomerContact") as HiddenField; //getting error in this line
string score = hiddenCustomerContact.Value;
int n = Int32.TryParse(score, out val);
string customerContact = "";
//check if any feedback pending
int pendingCount;
if (pendingCount > 0)
{
//ask to give feedback
}
else
{
//show worker contact
}
}
}

Hi it should work like this:
you can assign some value to the hidden variable as
<script type="text/javascript">
var somefunction = function () {
var hdnfldVariable = document.getElementById('hdnfldVariable');
hdnfldVariable.value = 'value from javascript';
}
</script>
in code behind you can read this field variable:
string variable = hdnfldVariable.Value;

Trying to get checkbox checked rows values from gridview using Javascript

I have gridview with checkbox as first column and I am trying to get the selected checkbox complete row values using Javascript function attached to check box mentioned below.
I tried with the different approach but got stuck in middle that is why I posted here again.
But some how I am not getting inside to the for loop and I am not sure where I am getting error in this code.
Javascript function:
function checkForVirtual(){
var GridView = document.getElementById('<%=gvPRCertInfo.ClientID %>');
if (GridView.rows.length > 0) {
alert('check');
for (Row = 1; Row < GridView.rows.length; Row++) {
alert("check 2 times");
if (GridView.rows[Row].cell[1].type == "checkbox") {
/// not getting into this
/// alert is not firing even if the checkbox is there
alert('inside');
if (GridView.rows[Row].cell[0].childNodes[0].checked) {
alert('checked');
var type = GridView.rows[Row].cell[3].childNodes[0].val();
alert(type);
}
}
}
}
}
This is my grid view:
<asp:GridView ID="gvPRCertInfo" runat="server" AutoGenerateColumns="False" GridLines="None"
OnRowDataBound="gvPRCertInfo_RowDataBound"
CssClass="data responsive">
<Columns>
<asp:TemplateField HeaderText="Select" SortExpression="">
<HeaderTemplate>
<asp:CheckBox ID="chkboxSelectAll" runat="server" AutoPostBack="true" OnCheckedChanged="chkboxSelectAll_CheckedChanged"/>
</HeaderTemplate>
<ItemTemplate>
<asp:CheckBox ID="chkCert" AutoPostBack="true" OnCheckedChanged="chkCert_CheckedChanged" OnClick="Javascript:checkForVirtual();" runat="server" />
<input type="hidden" id="hdnCertId" runat="server" value='<%# DataBinder.Eval(Container.DataItem, "CertId") %>' />
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="CertificateID" HeaderText="Certificate ID" HeaderStyle-HorizontalAlign="Center" />
<asp:BoundField DataField="partID" HeaderText="Part Number" HeaderStyle-HorizontalAlign="Center" />
..............................
</Columns>
.........................
.......................
</asp:GridView>
Would any one please help on this one?

<HeaderTemplate>
<asp:CheckBox ID="chkboxSelectAll" AutoPostBack="true" OnCheckedChanged="chkboxSelectAll_CheckedChanged" runat="server" Text="All" />
</HeaderTemplate>
<ItemTemplate>
<asp:CheckBox ID="chkCert" runat="server" Font-Size="XX-Small" />
</ItemTemplate>
</asp:TemplateField>
in cs file
protected void chkboxSelectAll_CheckedChanged(object sender, EventArgs e)
{
CheckBox chckheader = (CheckBox)gvPRCertInfo.HeaderRow.FindControl("chkboxSelectAll");
foreach (GridViewRow row in gvPRCertInfo.Rows)
{
CheckBox CheckBoxchckrw = (CheckBox)row.FindControl("chkCert");
if (chckheader.Checked == true)
{
CheckBoxchckrw.Checked = true;
}
else
{
CheckBoxchckrw.Checked = false;
}
}
}
get details on button click
protected void button_Click(object sender, EventArgs e)
{
try
{
int cnt = 0;
DataTable dt = new DataTable();
dt.Columns.Add("Certificate ID");
dt.Columns.Add("Part Number");
dt.Columns.Add("Part Description");
foreach (GridViewRow row in gvPRCertInfo.Rows)
{
if ((row.Cells[0].FindControl("chkCert") as CheckBox).Checked)
{
DataRow dr = dt.NewRow();
dr["Certificate ID"] = row.Cells[1].Text;
dr["Part Number"] = row.Cells[2].Text;
dr["Part Description"] = row.Cells[3].Text;
dt.Rows.Add(dr);
cnt++;
}
}
if (cnt <= 0)
{
DataRow dr = dt.NewRow();
dr["Certificate ID"] = gvPRCertInfo.SelectedRow.Cells[1].Text;
dr["Part Number"] = gvPRCertInfo.SelectedRow.Cells[2].Text;
dr["Part Description"] = gvPRCertInfo.SelectedRow.Cells[3].Text;
dt.Rows.Add(dr);
}
Session["Details"] = dt;
Response.Redirect("url");
}
catch (Exception ex)
{
}
}
your question is possibly copy of https://stackoverflow.com/a/47478969/8905879

getElementByID for templateField TextBox

i have used RowDataBound for gridview. Below is my C# code
protected void gvParameterValue_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
Label lblLocID = (Label)e.Row.FindControl("lblLocationID");
if(condition)
{
TextBox txtBox = (TextBox)e.Row.FindControl("txtValue");
txtBox.Attributes.Add("onchange", "ValueOnChange();");
}
}
}
Asp.Net code for gridview
<asp:UpdatePanel ID="updatePanel" runat="server">
<Triggers>
<asp:AsyncPostBackTrigger ControlID="btnSave" EventName="Click" />
</Triggers>
<ContentTemplate>
<asp:GridView ID="gvParameterValue" SkinID="GridView" runat="server" OnRowDataBound ="gvParameterValue_RowDataBound" AutoGenerateColumns="False">
<Columns>
<asp:TemplateField HeaderText="Location Name">
<asp:TemplateField HeaderText="Parameter Value">
<ItemTemplate>
<asp:TextBox ID="txtValue" SkinID="fineLineTextBox" TabIndex="1" runat="server" AutoPostBack="false"></asp:TextBox>
<%--<asp:TextBox ID="TextBox1" SkinID="fineLineTextBox" TabIndex="1" runat="server" OnTextChanged="textBox1_textChanged" AutoPostBack="true"></asp:TextBox>--%>
<asp:Label ID="lblPreDayVal" runat="server" Text='<%# Bind("PreviousValue") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
</ContentTemplate >
</asp:UpdatePanel>
js function as below and i have a problem
function ValueOnChange()
{
var val = document.getElementById('lblPreDayValue').value;
}
It gives error "Microsoft JScript runtime error: Object required"
i have tried all possible solutions from net but nothing works...

You've called getElementById on the ID lblPreDayValue. In your ASP.NET markup you've called it lblPreDayVal.
You might also want to use ClientID to ensure you get the correct ID generated by .NET

You can pass the ClientID from the server-side during the binding step in the gvParameterValue_RowDataBound method like this :-
TextBox txtBox = (TextBox)e.Row.FindControl("txtValue");
Label lblVal = (Label)e.Row.FindControl("lblPreDayVal");
txtBox.Attributes.Add("onchange", "ValueOnChange('" + lblVal.ClientID + "');");
And then inside the ValueOnChange method definition, pass the argument as cid (lets say).
function ValueOnChange(cid)
{
var val = document.getElementById(cid).innerHTML;
}

Try passing values at the RowBound event of gridview , You are trying to access getElementbyId('lblLocID') is not going to work because it's id will be change when row renders .
if (e.Row.RowType == DataControlRowType.DataRow)
{
Label lblLocID = (Label)e.Row.FindControl("lblLocationID");
Label lblPreDayValue =(Label)e.Row.FindControl("lblPreDayValue");
if (lblLocID.Text.Equals("154") || lblLocID.Text.Equals("168") || lblLocID.Text.Equals("178"))
{
TextBox txtBox = (TextBox)e.Row.FindControl("txtValue");
txtBox.Attributes.Add("onchange", "ValueOnChange(" + lblPreDayValue.ClientID + ");");
}
}
After passing ClientID to function
//Or you can directly pass the value of label and assign .
function ValueOnChange(ClntID)
{
var val = document.getElementById('ClntID').innerHTML;
}

Try to use
function ValueOnChange()
{
var val = document.getElementById('#<%= lblPreDayVal.ClientID %>').innerHTML;
}
If the above din work then
function ValueOnChange()
{
var val = document.getElementById('lblPreDayVal').innerHTML;
}

Enable/disable text box placed in gridview on check event of check box with javascript

I have gridview which contains check box and textbox in different item template fields. Text boxes will be disbled when grid is loaded. Now what I want is, when user checks any of the check box, respected textbox in that particular row should be enabled. When user unchecks the checked checkbox, again the textbox should get clear and disable. Now when user clicks on the save button, a javascript should validate all the textbox whose respected checkboxes are checked.
Validation is
(1)Text boxes should not be empty
(2)It should allow only character and space(I want to enter name in that text box). How can I write java script to perform all this task. I am novice to javascript and completely unaware of its concept.
Thanks in advance

<script type="text/javascript">
var nameRegex = /^[a-zA-Z ]+$/;
function validateName(sender, args) {
args.IsValid = nameRegex.test(args.Value);
}
</script>
<asp:GridView runat="server" ID="GridView1" AutoGenerateColumns="false" DataKeyNames="Id" >
<Columns>
<asp:TemplateField >
<ItemTemplate>
<asp:CheckBox runat="server" AutoPostBack="true" OnCheckedChanged="SelectRow" />
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="Id" HeaderText="Id" />
<asp:TemplateField HeaderText="Name" >
<ItemTemplate>
<asp:TextBox runat="server" ID="NameTextBox" Enabled="false" Text='<%# Eval("Name") %>' />
<asp:CustomValidator runat="server" ID="NameValidator" ControlToValidate="NameTextBox"
ValidateEmptyText="true" Text="!" Display="Static" Enabled="false"
ClientValidationFunction="validateName" OnServerValidate="ValidateName" />
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
public partial class WebForm1 : System.Web.UI.Page
{
private static readonly Regex nameRegex = new Regex("^[a-zA-Z ]+$");
protected void ValidateName(object source, ServerValidateEventArgs args)
{
args.IsValid = nameRegex.IsMatch(args.Value);
}
protected void SelectRow(object sender, EventArgs e)
{
Page.Validate();
var checkBox = (CheckBox)sender;
if (Page.IsValid || !checkBox.Checked)
{
var textBox = (TextBox)checkBox.NamingContainer.FindControl("NameTextBox");
var nameValidator = (CustomValidator)checkBox.NamingContainer.FindControl("NameValidator");
textBox.Enabled = checkBox.Checked;
nameValidator.Enabled = checkBox.Checked;
if (!checkBox.Checked)
textBox.Text = "";
}
else
{
checkBox.Checked = false;
}
}
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
GridView1.DataSource = from item in Enumerable.Range(0, 10)
select new
{
Id = item,
Name = ""
};
GridView1.DataBind();
}
}
}

set value of dropdown lists in Gridview with javascript

I have a dropdownlist and a gridview with a drop down list in every row. I have removed other cols in Grid for simplicity.
Whenever a new value in the dropdownlist is selected I would like to set all of the dropdownlists in the gridview to that same value via javascript. (Yea both the dropdownlist outside the gird and the ones inside the grid are populated by the same data source)
The dropdownlist:
<asp:DropDownList onchange="javascript:onJDSelection();" ID="DropDownList3" runat="server"
DataSourceID="SqlDataSource4" DataTextField="circt_cstdn_nm"
DataValueField="circt_cstdn_user_id">
</asp:DropDownList>
The GridView:
<asp:GridView ID="GridView2" runat="server" AutoGenerateColumns="False"
DataSourceID="SqlDataSource1" onrowdatabound="GridView2_RowDataBound">
<Columns>
<asp:TemplateField HeaderText="Change to Job Designer" SortExpression="circt_Cstdn_nm">
<EditItemTemplate>
<asp:TextBox ID="TextBox1" runat="server" Text='<%# Bind("circt_Cstdn_nm") %>'></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:DropDownList ID="ddl_jd" runat="server" DataSourceID="SqlDataSource4" DataTextField="CIRCT_CSTDN_NM"
DataValueField="CIRCT_CSTDN_user_id"></asp:DropDownList>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
My current attempt:
function onJDSelection() {
var jd = document.getElementById('ctl00_MAIN_DropDownList3').Text;
var grid = document.getElementById('ctl00_MAIN_GridView2');
for (var i = 1; i < grid.rows.length; i++) {
grid.rows[i].cells[0].getElementsByTagName("*")[1].selectedText = jd;
}
}
any ideas?
Thanks!
Update: I tried this.
<script type="text/javascript">
function onJDSelection() {
var jd = document.getElementById('ctl00_MAIN_DropDownList3').Text;
var dropDowns = jQuery('input[id^=ctl00_MAIN_GridView2_ddl_jd]');
alert("test");
alert(dropDowns);
var i = 0;
dropDowns.each(function () {
alert(i);
i++;
jQuery('#' + jQuery(this) + ':first-child').text(jd);
});
}
</script>
When clicking on the dropdown I get an alert that says "test" and an alert that says "[Object object]" However nothing happens with the dropdowns in the grid and the alert(i) never fires.

I suggest to change the selected values for the dropdownlists from code behind like this:
protected void DropDownList3_SelectedIndexChanged(object sender, EventArgs e)
{
foreach (GridViewRow gvRow in GridView2.Rows)
{
Control ctrl = gvRow.FindControl("ddl_jd");
DropDownList ddl = ctrl as DropDownList;
if (ddl != null)
ddl.SelectedIndex = DropDownList3.SelectedIndex;
}
}
Also make sure to set AutoPostBack="true" for DropDownList3.
Another approach (that is not very clean or simple) is to add the following code into the Page_Load method (and remove the script block containing onJDSelection function from the .aspx file):
if (!Page.IsPostBack)
{
string functionContent = "<script language=javascript> function onJDSelection()" +
"{ var selectedIndex = document.getElementById('" + DropDownList3.ClientID + "').selectedIndex;" +
"var grid = document.getElementById('" + GridView2.ClientID + "'); " +
"for (var i = 1; i < grid.rows.length; i++) " +
"{ var selObj = grid.rows[i].cells[0].getElementsByTagName(\"*\")[0]; selObj[selectedIndex].selected = true;} "+
"}</script>";
Page.RegisterStartupScript("MyScript", functionContent);
DropDownList3.Attributes.Add("onchange", "onJDSelection()");
}.
Note that is this case the ID used for retrieving DropDownList3 and GridView2 in javascript are sent from code behind as is not very safe to rely on server control ID's generated by ASP .NET. In case you want to save the dropdownlists values (that are changed using javascript) you will also need additional code.
It works based on the following body for aspx page:
<body>
<form id="form1" runat="server">
<div>
<asp:DropDownList ID="DropDownList3" runat="server"
DataSourceID="SqlDataSource1" DataTextField="circt_cstdn_nm"
DataValueField="circt_cstdn_user_id" onselectedindexchanged="DropDownList3_SelectedIndexChanged">
</asp:DropDownList>
<asp:GridView ID="GridView2" runat="server" AutoGenerateColumns="False" DataSourceID="SqlDataSource1"
onrowdatabound="GridView2_RowDataBound" DataKeyNames="circt_cstdn_user_id">
<Columns>
<asp:TemplateField HeaderText="Change to Job Designer" SortExpression="circt_Cstdn_nm" >
<EditItemTemplate>
<asp:TextBox ID="TextBox1" runat="server" Text='<%# Bind("circt_Cstdn_nm") %>'></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:DropDownList ID="ddl_jd" runat="server" DataSourceID="SqlDataSource1" DataTextField="CIRCT_CSTDN_NM"
DataValueField="CIRCT_CSTDN_user_id"></asp:DropDownList>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
<asp:SqlDataSource ID="SqlDataSource1" runat="server"
ConnectionString="<%$ ConnectionStrings:TestConnectionString %>"
SelectCommand="SELECT * FROM [test]"></asp:SqlDataSource>
</div>
</form>

If possible, I'd suggest that you use jQuery. It has a multitude of partial name selectors and input selectors that you can use to get all of your DropDowns. You could use something like:
function onJDSelection() {
var jd = document.getElementById('ctl00_MAIN_DropDownList3').Text;
var dropDowns = jQuery('input[id^=ctl00_MAIN_GridView2_ddl_jd]');
dropDowns.each(function() {
jQuery('#' + jQuery(this) + ':first-child').text(jd);
});
}