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How to get CheckBox value from GridView when CheckBox selected

I have GridView filled automatically as
<asp:GridView ID="gvValues" runat="server"
OnRowDataBound="gvValues_RowDataBound"
OnPageIndexChanging="gvValues_PageIndexChanging"
<Columns>
<asp:TemplateField HeaderText="#">
<ItemTemplate>
<%# gvValues.PageSize*gvValues.PageIndex+ Container.DisplayIndex+1 %>
<asp:CheckBox ID="chkProduct" runat="server" CssClass="chkProduct"/>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="online" meta:resourcekey="Online">
<ItemTemplate >
<asp:CheckBox ID="chkProductonline" runat="server" OnCheckedChanged ="chkProductonline_CheckedChanged" AutoPostBack="true"/>
</ItemTemplate>
</asp:TemplateField>
What I need is when I click on the chkProductonline checkbox, to fire an event and get the chkProductonline and chkProducton values. I have tried this but it always gives me null.
protected void chkProductonline_CheckedChanged(object sender, EventArgs e)
{
var chkProductonline = FindControl("chkProductonline") as CheckBox;
// bool ischeck = chkProductonline.Checked;
var chkProduct = gvValues.FindControl("chkProduct") as CheckBox;
}
I can't loop the GridView. I need to do this one-by-one. Is there another way to do that?

You can try this:
protected void chkProductonline_CheckedChanged(object sender, EventArgs e)
{
CheckBox chkProductonline = sender as CheckBox;
...
CheckBox chkProduct = chkProductionLine.NamingContainer.FindControl("chkProduct") as CheckBox;
...
}

You need to call FindControl on a specific row. You will not be able to call it on the entire GridView because there exists repeating content (i.e. multiple chkProductionlines and chkProducts). A row knows of its checkboxes, and not of the others.
So what you can do is first get the CheckBox that called the event (your sender parameter, chkProductionline) and use its NamingContainer. Since it is contained in a GridView row, cast the row as such as use it to find the other controls you may need.
protected void chkProductonline_CheckedChanged(object sender, EventArgs e)
{
CheckBox chkProductionline = (CheckBox)sender;
GridViewRow row = (GridViewRow)chkProductionline.NamingContainer;
CheckBox chkProduct = (CheckBox)row.FindControl("chkProduct");
}

ItemList FindControl working for 1 item

I have a LinkButton within my ItemTemplate of my ListView:
<asp:ListView ID="lvNotification" runat="server">
<ItemTemplate>
<asp:LinkButton runat="server" ID="lbReject" OnClick="Reject_Click" CommandArgument='<%# Eval("offerID") %>' Text="Reject" />
</ItemTemplate>
</asp:ListView>
Then in my code I have:
protected void Reject_Click(object sender, EventArgs e)
{
var lbreject = lvNotification.Items[0].FindControl("lbReject") as LinkButton;
string c = lbreject.CommandArgument;
}
The ListView retrieves 4 rows correctly, and I have placed the Eval("offerID") and it shows an offerID for each item in the list, however when I place it as the CommandArgument in the LinkButton and debug it, it shows the value 1 on ever item in the ListView, I am trying to place the offerID in each LinkButton CommandArgument and be able to access it, but I cannnot do so.
What am I doing wrong?

That is because you are always checking the first item (0 index). You can get the LinkButton from the sender and check its command argument.
protected void Reject_Click(object sender, EventArgs e)
{
var lbreject = (LinkButton)sender;
string c = lbreject.CommandArgument;
}

Here actually OnItemCommand event of ListView can be handy. This way you can control all events from the single point:
<asp:ListView ID="lvNotification" OnItemCommand="lvNotification_OnItemCommand" runat="server">
<ItemTemplate>
<asp:LinkButton runat="server" ID="lbReject" CommandName="Reject_Click" CommandArgument='<%# Eval("offerID") %>' Text="Reject" />
</ItemTemplate>
</asp:ListView>
protected void lvNotification_OnItemCommand(object sender, ListViewCommandEventArgs e)
{
if (String.Equals(e.CommandName, "Reject_Click"))//or any other event
{
LinkButton lbreject = (LinkButton) sender;
string c = lbreject.CommandArgument;
}
}

Passing Gridview LinkButton ID to Modal PopUp in ASP.NET

I have a button like this in my gridview,
<asp:LinkButton runat="server" ID="lnkCustDetails" Text='<%# Eval("CustomerID") %>' OnClick="lnkCustDetails_Click" />
and I get the id like this:
protected void lnkCustDetails_Click(object sender, EventArgs e)
{
LinkButton lb = sender as LinkButton;
string custID = lb.Text;
lblCustValue.Text = custID;
ModalPopupExtender1.Show();
}
My problem is, what can I use instead of having the id in Text='<%# Eval("CustomerID") %>' because this displays the id of the customer in the linbutton, when I want the link button to display "Details"

You can switch to handling commands instead of clicks:
<asp:LinkButton runat="server" ID="lnkCustDetails"
Text='Details'
CommandArgument='<%# Eval("CustomerID") %>'
OnCommand="lnkCustDetails_Click" />
And to get the id:
protected void lnkCustDetails_Click(object sender, EventArgs e)
{
LinkButton lb = sender as LinkButton;
string custID = lb.CommandArgument;
lblCustValue.Text = custID;
ModalPopupExtender1.Show();
}
One note though: I am not sure if you can handle LinkButton's command directly if it lives inside the grid view. You might need to subscribe to grid view's On Command instead - please check.

FormView.DataItem is null on postback

I am using a LinqDataSource and a FormView with paging enabled on an ASP.NET page. I am trying to access the FormView's DataItem property on PageLoad and I have no trouble on the first page load, but as soon as I use the Next/Prev page button (causing a postback) on the FormView the DataItem property is null, even if there a record showing in the FormView. Any ideas why it works fine on the first page load but not on a postback?
If you're curious what my PageLoad event looks like, here it is:
protected void Page_Load(object sender, EventArgs e)
{
Label lbl = (Label)fvData.FindControl("AREALabel");
if (fvData.DataItem != null && lbl != null)
{
INSTRUMENT_LOOP_DESCRIPTION record = (INSTRUMENT_LOOP_DESCRIPTION)fvData.DataItem;
var area = db.AREAs.SingleOrDefault(q => q.AREA1 == record.AREA);
if (area != null)
lbl.Text = area.AREA_NAME;
}
}

The object you bind to any data-bound control won't be persisted in the page's ViewState
Therefore, on subsequent posts the DataItem property will be null unless you re-bind the control
This property will contain a reference to the object when the control is bound.
Usually you would need to access this property if you want to do something when the objects is bound, so you need to react to the DataBound event
Example:
Output
Code behind
protected void ds_DataBound(object sender, EventArgs e)
{
var d = this.fv.DataItem as employee;
this.lbl.Text = d.lname;
}
ASPX
<asp:LinqDataSource ID="lds" runat="server"
ContextTypeName="DataClassesDataContext"
TableName="employees"
>
</asp:LinqDataSource>
<asp:FormView runat="server" ID="fv" DataSourceID="lds" AllowPaging="true"
OnDataBound="ds_DataBound">
<ItemTemplate>
<asp:TextBox Text='<%# Bind("fname") %>' runat="server" ID="txt" />
</ItemTemplate>
</asp:FormView>
<br />
<asp:Label ID="lbl" runat="server" />

Your data will not be preserved on PostBack. You'll need to rebind the FormView in the PageIndexChanging event using something like:
protected void FormView_PageIndexChanging(object sender, FormViewPageEventArgs e)
{
FormView.PageIndex = e.NewPageIndex;
//rebind your data here
}

How to add web user controls to repeater

Scenario:
UsrControl: custom user control, which contains a textbox and a button, rederend horizontally (in one line).
UsrControlContainer: custom user control, which should be able to display multiple UsrControl objects (each object in seperate line, so the Seperator template will probably be <br />. This control also contains a button, which adds new UsrControl to the collection.
My code:
<asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click"/>
<asp:Repeater ID="rptExample" runat="server">
<ItemTemplate>
</ItemTemplate>
<SeparatorTemplate><br /></SeparatorTemplate>
</asp:Repeater>
And:
protected void Button1_Click(object sender, EventArgs e)
{
rptExample.DataSource = new List<UsrControl> {new UsrControl(), new UsrControl()};
rptExample.DataBind();
}
Simple question - what should I put in ItemTemplate to make this work?
Edit - I also want to pass some parameters to UsrControl before rendering it.

<asp:Repeater ID="rptExample" runat="server">
<ItemTemplate>
<uc:UsrControl runat="server" />
</ItemTemplate>
<SeparatorTemplate><br /></SeparatorTemplate>
</asp:Repeater>
protected void Button1_Click(object sender, EventArgs e)
{
rptExample.DataSource = Enumerable.Range(0, 2);
rptExample.DataBind();
}

Following your question in answer. You can catch every binding object in ItemDataBound event. So for example, as i used, set whole object as user control property.
protected void PersonesRepeater_ItemDataBound(object sender, RepeaterItemEventArgs e)
{
if (e.Item.ItemType == ListItemType.Item || e.Item.ItemType == ListItemType.AlternatingItem)
{
PersonLine line = (PersonLine)e.Item.FindControl("Person1");
line.Person = e.Item.DataItem as Osoba;
}
}
Ofcourse, you have to add the event handler to your repeater:
<asp:Repeater runat="server" ID="PersonesRepeater" OnItemDataBound="PersonesRepeater_ItemDataBound"><ItemTemplate>
<my:Person ID="Person1" runat="server" />
</ItemTemplate>
</asp:Repeater>