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trigger an eventhandler on postback c#

I am pretty new to c# programming.
I have an issue that follows:
I have a GridView on a web form, a DropDownList and a Label control. When i select a value from a DDL a Grid View is populated with rows from the database that equal the DDL condition(in my case DDL represent Countries, GV lists the Cities).
When i delete the last City from a GV using a built in GV Delete function i would like to automatically write in a Label that there are no more Cities in selected Country.
How can i achieve that?
I tried to put
protected void GridView1_RowDeleted1(object sender, GridViewDeletedEventArgs e)
{
if (GridView1.Rows.Count == 0)
{
LabelGrid.Text = "No more cities.";
}
}
but it didn't work.
Thanks for your help

Consider using PreRender event, when that event runs the Row.Count property contains the correct value. (decremented after delete)
protected void GridView1_PreRender(object sender, EventArgs e)
{
if (GridView1.Rows.Count == 0)
{
LabelGrid.Text = "No more cities.";
}
}

GridView row values not changed after update

I want to update row in GridView with this code but after editing GridView not changes:
protected void res_RowUpdating(object sender, GridViewUpdateEventArgs e)
{
//Retrieve the table from the session object.
DataTable dt = (DataTable)Session["dt"];
GridViewRow row =res.Rows[e.RowIndex];
dt.Rows[row.DataItemIndex]["name"] = ((TextBox)(row.Cells[6].Controls[0])).Text;
dt.Rows[row.DataItemIndex]["dewey"] = ((TextBox)(row.Cells[5].Controls[0])).Text;
*dt.Rows[row.DataItemIndex]["subject"] = ((TextBox)(row.Cells[4].Controls[0])).Text;
Session["dt"] = dt;
res.EditIndex = -1;
res.DataSource = dt;
res.DataBind();
}
my Page_Load:
protected void Page_Load(object sender, EventArgs e)
{
DataTable dt;
if (!IsPostBack)
{
dt= Converter.ListBooks(new classes.Book().GetAll());
Session["dt"] = dt;
res.DataSource = dt;
res.DataBind();
}
else
{
dt=(DataTable)Session["dt"];
res.DataSource = dt;
res.DataBind();
}
}
for example I changed line that have * to this:
dt.Rows[row.DataItemIndex]["subject"] = "tx";
and after edit "subject" column changed to "tx", so I don't know why ((TextBox)(row.Cells[4].Controls[0])).Text return TextBox's text before edit?

Because you're calling DataBind(); method each time page refreshed (POST or GET), let me explain more if user put the new value in the TextBox and click on update button to trigger res_RowUpdating even Page_Load will fire and bind the Gird with database values which is the old values and neglect the user input value.

I think, you just need to rebind the grid

Remove the else part in your page_load.
Should do it for you.
You are binding the Grid every time there is a postback which is not required.

Maybe changes are done but the form is not being updated.
Try putting gridview control inside an Update Panel Control and call UpdatePanel.Update().
When you work with a web control, what you see can be different from what actually is because changes in data are not autoupdated in the presentation layer.
To solve this "problem" you can make a postback (retrieving everything) of the whole page, but this is like killing a fly with a bazooka because you do not need everything, just what has been updated, so for this purpose there are several tool that allow you to make partial updates, for example the AJAX control: UpdatePanel.
Hope it helps.
Update: Call the AcceptChanges() method on the DataTable and erase the else branch on the Page_Load after if(!PostBack)

Call the AcceptChanges() method of the DataTable and then bind the GridView.

gridview databinding problem

i am using asp.net with c#
and i want to bind my data to the gridview
i have success fully done that by wizard
but now it is show me this error
protected void Button1_Click(object sender, EventArgs e)
{
SqlDataAdapter dbadapter = null;
DataSet dbdata = new DataSet();
using (SqlConnection dbconn = new SqlConnection("Server=CJ\\SQLEXPRESS;Database=elligiblity;User ID=sa;Password=123;Trusted_Connection=False;"))
{
dbadapter = new SqlDataAdapter("select * from Main_Table", dbconn);
dbadapter.Fill(dbdata);
}
GridView1.DataSource = dbdata;
GridView1.DataBind();
}
i am getting this error
Both DataSource and DataSourceID are defined on 'GridView1'. Remove one definition

You cannot specify custom binding from code if gridview is already binded to a datasource. Either remove DataSourceID in gridview properties from your aspx page or change the select command of the sql datasource to which it is binded from code like,
protected void Button1_Click(object sender, EventArgs e)
{
sdsFtrtDet.SelectParameters.Clear(); // Clear any innitial parameters of your sql datasource which is binded with gridview
sdsFtrtDet.SelectCommand = "select * from tableA"; //Specify new query
sdsFtrtDet.DataBind(); // Data Bind
}
Cheers.
Edit
You probably are not seeing your gridview because you would have used template fields binded with datasource ? You can use another gridview to bind with your 2nd query. Leave the 1st gridview as it is so you wont get in trouble with template fields.
Cheers.

So that means that in your markup, you're specifying a value for DataSourceID, but then in the code you've shown, you're setting DataSource. DataSourceID and DataSource are mutually exclusive.

Nesting Repeater in Gridview: Hiding gridview row and repeater header if data is not there in repeater

I have nested a repeater control in Gridview. Right now it is showing gridview rows and repeater header for every case(whether data is there or not for that particular grid view row in the repeater control). I want to hide the gridview row and repeater control header when there is no data present for that particular gridview row.
Thanks,
That case I handled at code level by filtering the resulted data table.
Now the another problem I am facing:
I have allowed the paging on the gridview i.e. pagesize 3.
When page loads it works fine, but when I go to page 2 then it generates following error:
Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index
Below is the code to fill the grid, paging and fill repeater on rowdatabound event of grid.
private void FillGrid()
{
clsCustomFunctions objShort = new clsCustomFunctions();
grd1.DataSource = objShort.GetAll();
}
protected void grd1_PageIndexChanging(object sender, GridViewPageEventArgs e)
{
try
{
FillGrid();
grd1.PageIndex = e.NewPageIndex;
grd1.DataBind();
}
catch (Exception ex)
{
lblMsg.Text = ex.Message;
}
}
protected void grd1_RowDataBound(object sender, GridViewRowEventArgs e)
{
clsCustomFunctions objShort = new clsCustomFunctions();
if (e.Row.RowType == DataControlRowType.DataRow)
{
((HtmlTable)e.Row.FindControl("gridTable")).BgColor = "#006699";
Repeater rpt = (Repeater)e.Row.FindControl("rpt1");
rpt.DataSource = objShort.GetResult(Convert.ToInt32(grd1.DataKeys[e.Row.DataItemIndex].Value));
rpt.DataBind();
}
}
grd1.DataKeys[e.Row.DataItemIndex].Value line is throwing error. How to handle this to pass values of page 2 only.

Try handling the OnRowDataBound event of the grid. This gives you a GridViewRowEventArgs object (say e).
You can then look at e.Row.DataItem to get the data it is binding to to check if you need to hide the header.
You can use e.Row.FindControl("RepeaterName") to get the repeater to manipulate as you want.

GridView paging inside an UpdatePanel or PlaceHolder components

I'm new to ASP.NET.
Im developing ASP.NET C# web form which creating GridView components dynamically and filling them using the data received from my webservice.
I'm creating these GridView components programmatically in server-side (cs file)- it has to be flexible - 1 GridView and sometimes 10 GridView components.
The problem occurs when I'm trying to add pagination - whenever the user clicks the "next" page, the whole page is getting refreshed because of a postBack and I'm loosing all my data and the page returns Blank/Empty.
I used PlaceHolder to hold the GridView components, while searching for a solution, I found UpdatePanel as a better alternative - as far as I understand the page can be partially refreshed - which means that only the UpdatePanel has to be refreshed...but it doesn't work.
The following code sample is my TEST, the UpdatePanel is the only component initiated in the client side (.aspx page), the rest initiated programmatically in .cs .
how can I solve the issue described above?
Why does the whole page is getting refreshed and I'm loosing my data?
can you recommend another way? can provide me with any code sample?
If I'm not rebuilding the GridView, it doesn't work...
Here is my Default.aspx.cs
public partial class TestAjaxForm : System.Web.UI.Page
{
DataTable table;
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
bindGridView();
}
public void bindGridView()
{
GridView gridView1 = new GridView();
gridView1.AutoGenerateColumns = true;
gridView1.PageSize = 2;
gridView1.AllowPaging = true;
gridView1.PagerSettings.Mode = PagerButtons.Numeric;
gridView1.PagerSettings.Position = PagerPosition.Bottom;
gridView1.PagerSettings.PageButtonCount = 10;
gridView1.PageIndexChanging += new GridViewPageEventHandler(this.GridView1_PageIndexChanging);
table = new DataTable();
table.Columns.Add("FirstName");
table.Columns.Add("LastName");
DataRow row = table.NewRow();
row["FirstName"] = "John";
row["LastName"] = "Johnoson";
table.Rows.Add(row);
row = table.NewRow();
row["FirstName"] = "Johnny";
row["LastName"] = "Marley";
table.Rows.Add(row);
row = table.NewRow();
row["FirstName"] = "Kate";
row["LastName"] = "Li";
table.Rows.Add(row);
panel.ContentTemplateContainer.Controls.Add(gridView1);
gridView1.DataSource = table;
gridView1.DataBind();
}
protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)
{
GridView gridView1 = (GridView)sender;
gridView1.PageIndex = e.NewPageIndex;
gridView1.DataSource = table;
gridView1.DataBind();
}
}
Thank you.

If you want a custom GridView approach to work, you have to recreate and rebind the grid on every page load... that's the problem with dynamic Grids... Dynamic controls don't retain their viewstate, but if you added the grid and dynamically generated the columns, that would work easier for you (because I think it may dynamically remember the columns, or you can set AutoGenerateColumns to true, and it brings in your data row column names).
HTH

You should create your GridView and add it to the control tree in the PreInit or Init event handler so that they have a chance to properly bind to ViewState, and it should be done whether or not there's a postback: if you don't add them in a postback, they obviously won't be there to display anything.
DataBinding can happen later in the page life cycle.
Paging only seems to work if you also use an ObjectDataSource; I've never been able to get it to work with a GridView by itself.

I think the easiest thing to do is have the gridview declared in the aspx page inside the place holder, while the place holder is also contained inside the update panel.
For what I can see, John is not doing anything that can't be declared in the markup itself so that shouldn't be a problem. If for some reason the gridview should not be displayed on the screen, it suffices to set the Visible property of the placeholder to false.
As far as paging is concerned, as RickNz correctly points out, it will only retain the state if you bind the gridview to either a LinqDatasource, SqlDatasource or ObjectDatasource but if you bind it to custom business objects, what you need to do is save the data in Session and rebind it again on PageIndexChanged.
In pseudo code, would be sometging like this.
Page_load
{
If (!IsPostBack)
Binddata();
}
private void Binddata()
{
var data = Getdata();
Gridview1.DataSource= data;
Gridview.DataBind();
Session["data"]=data; // cache the data
}
protected void Gridview1_indexchanged(object sender, GridviewPageEventArgs e)
{
var data= Session["data"];
Gridview1. DataSource=data;
Gridview1.DataBind();
GridView1.PageIndex=e.NewPageIndex;
}