Firing events for child controls inside a DataGrid

G

glenn

Hi folks,

Apparently, when you have a child control inside of a DataGrid, the event
handler for the control does not work. I want to put a child control
(checkbox, dropdownlist, etc.) into my datagrid and have the value selected
to immediately fire an event and immediately update my database.

For example, if a checkbox is checked (in a DataGrid there would be a
checkbox column with a checkbox in each row), an event would be fired to
update the database which in this case would have a boolean value indicating
whether the checkbox had been checked or unchecked.

thanks,
Glenn
 
A

Alessandro Zifiglio

hi glenn, you can either try to hookup the event in your declarative code,
this will fire, regardless of the fact that its a child control of your
datacontrol. so, you can try something like this :
<asp:CheckBox id="CheckBox1" runat="server"
AutoPostBack="True"
OnCheckedChanged="CheckBox1_CheckedChanged"/>

code behind :

protected void CheckBox1_CheckedChanged(object sender, EventArgs e)
{
CheckBox cb1 = (CheckBox)sender;
if (cb1 != null)
Response.Write(cb1.Checked.ToString());
}


You can do the same for your dropdownlist too.
Command events are bubbled up in the datagrids ItemCommand method, giving
you a central location to look for events fired by child controls in your
templated datacontrol, however this wont work with the checkbox control or
your dropdownlist. Unlike the button, linkbutton and ImageButton which raise
a command event, this is not supported on the checkbox or the dropdownlist.
The ItemCommand method exposed by the datagrid only bubbles up command
events, since this allows you to set CommandName and CommandArgument values
to the controls posting back, in turn allowing you to check what control
fired the postback event in the ItemCommand method and take action
accordingly.

for more on the datagrids ItemCommand you can reference, the following
document on msdn. Specially take a close look at the ItemsGrid_Command
method in the sample code provided :
http://msdn2.microsoft.com/en-us/library/system.web.ui.webcontrols.datagrid.itemcommand.aspx

Regards,
Alessandro Zifiglio
http://www.AsyncUI.net
 
G

glenn

Alessandro,

If you know VB, maybe you can tell me how
to handle the line
Dim cb As CheckBox = CheckBox (sender) where I get a compiler error
'CheckBox' is a type and cannot be used as an expression'

I used the following code in VB and I get a compiler error

protected Sub Check_Clicked(sender as object, e as System.EventArgs)
Dim cb As CheckBox = CheckBox (sender)
Response.Write(cb.Checked.ToString());
end sub


thanks,
glenn
 
G

glenn

Alessandro,

Ok. I now know how to cast in VB.

I would write:
CType(sender, CheckBox)

but I am still not getting the event to fire. I have OnCheckChanged set =
to "Changed_Click" in the <asp:CheckBox html.

thanks,
glenn
 
A

Alessandro Zifiglio

hi glenn, it works for me and works well. Here is a test you can try
yourself.

Regards,
Alessandro Zifiglio
http://www.AsyncUI.net


<%@ Page Language="VB" %>
<%@ Import Namespace="System.Data" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<script runat="server">
Function CreateDataSource() As ICollection
Dim dt As New DataTable()
Dim dr As DataRow
dt.Columns.Add(New DataColumn("StringValue1", GetType(String)))
dt.Columns.Add(New DataColumn("StringValue2", GetType(String)))
Dim i As Integer
For i = 0 To 5
dr = dt.NewRow()
dr(0) = "Checkbox " + i.ToString()
dr(1) = "TextBox " + i.ToString()
dt.Rows.Add(dr)
Next i

Dim dv As New DataView(dt)
Return dv
End Function

Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)

If Not IsPostBack Then
' Load this data only once.
DataGrid1.DataSource = CreateDataSource()
DataGrid1.DataBind()
End If
End Sub 'Page_Load

Protected Sub CheckBox1_CheckedChanged(ByVal sender As Object, ByVal e
As System.EventArgs)
Dim cb1 As CheckBox = CType(sender, CheckBox)

If (cb1 IsNot Nothing) Then
Response.Write(cb1.Checked)
' Lets get a reference to the tableCell holding our checkbox and
then find our textbox control
' which happens to be within the same tablecell.
' another way to achieve a better result is to
' reference cb1.NamingContainer, instead of cb1.Parent
' since that would return a DataGridItem,
' the entire row, and then we can navigate through
' the cells collection.
' this is just in case you want to do something with
' data in the current row holding your checkbox.
' i dont mean to confuse you with the following extra few lines
here.
Dim tc As TableCell = CType(cb1.Parent, TableCell)
Dim tb1 As TextBox = CType(tc.Controls(3), TextBox)
If (tb1 IsNot Nothing) Then
Response.Write(tb1.Text)
End If

End If
End Sub
</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<h3>
DataGrid Example</h3>
<b>Product List</b>
<asp:DataGrid ID="DataGrid1" BorderColor="black" BorderWidth="1"
CellPadding="3"
AutoGenerateColumns="false" runat="server">
<HeaderStyle BackColor="#00aaaa"></HeaderStyle>
<Columns>
<asp:TemplateColumn>
<ItemTemplate>
<asp:CheckBox AutoPostBack="true" ID="CheckBox1"
Text='<%# DataBinder.Eval(Container.DataItem, "StringValue1") %>'
OnCheckedChanged="CheckBox1_CheckedChanged"
runat="server" />
<asp:TextBox ID="TextBox1"
Text='<%#DataBinder.Eval(Container.DataItem, "StringValue2")%>'
runat="server"></asp:TextBox>
</ItemTemplate>
</asp:TemplateColumn>
</Columns>
</asp:DataGrid>
</div>
</form>
</body>
</html>
 

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