Gridview Events in Asp.net Web Applications

Introduction

I have seen lot of beginners struggle with GridView and it is not working. To solve this to some extent, I have created an application with most of the events and properties of GridView. This may be helpful for getting a clear idea about working with GridView. This application also has a few JavaScript code snippets and stylesheets which may be useful to add some values to the GridView. Hope this article will be simple and sufficient.

What is a GridView?

The DataGrid or GridView control displays data in tabular form, and it also supports selecting, sorting, paging, and editing the data inside the grid itself. The DataGrid or GridView generates a BoundColumn for each field in the data source (AutoGenerateColumns=true). By directly assigning the data source to the GridView, the data can be rendered in separate columns, in the order it occurs in the data source. By default, the field names appear in the grid's column headers, and values are rendered in text labels. A default format is applied to non-string values and it can be changed.

GridView Fields

Column Name	Description
BoundColumn	To control the order and rendering of columns.
HyperLinkColumn	Presents the bound data in HyperLink controls
ButtonColumn	Bubbles a user command from within a row to the grid event handler
TemplateColumn	Controls which controls are rendered in the column
CommandField	Displays Edit, Update, and Cancel links in response to changes in the DataGrid control's EditItemIndex property.

BoundColumn

By explicitly creating a BoundColumn in the grid's Columns collection, the order and rendering of each column can be controlled. In the BoundField properties, when the DataField and the SortExpressions are given, sorting and rendering the data can be easily done.

HyperLinkColumn

A HyperLinkColumn presents the bound data in HyperLink controls. This is typically used to navigate from an item in the grid to a Details view on another page by directly assigning the page URL in NavigationUrl or by rendering it from the database.

TemplateColumn

With a TemplateColumn, the controls which are rendered in the column and the data fields bound to the controls can be controlled. By using the TemplateColumn, any type of data control can be inserted.

By clicking the Edit Templates option, it opens the Template field where we can see controls that can be added like Label, CheckBox, and even a GridView.

CommandField

The EditCommandColumn is a special column type that supports in-place editing of the data in one row in the grid. EditCommandColumn interacts with another property of the grid: EditItemIndex. By default, the value of EditItemIndex is -1, meaning none of the rows (items) in the grid are being edited. If EditItemIndex is -1, an "edit" button is displayed in the EditCommandColumn for each of the rows in the grid.
When the "edit" button is clicked, the grid's EditCommand event is thrown. It's up to the programmer to handle this event in the code. The typical logic sets EditItemIndex to the selected row, and then rebinds the data to the grid.
When EditItemIndex is set to a particular row, the EditCommandColumn displays "update" and "cancel" buttons for that row ("edit" is still displayed for the other rows). These buttons cause the UpdateCommand and CancelCommand events to be thrown, respectively.

Different Types of Events

Name	Description
DataBinding	Occurs when the server control binds to a data source. (Inherited from Control.)
DataBound	Occurs after the server control binds to a data source. (Inherited from BaseDataBoundControl.)
Disposed	Occurs when a server control is released from memory, which is the last stage of the server control lifecycle when an ASP.NET page is requested. (Inherited from Control.)
Init	Occurs when the server control is initialized, which is the first step in its lifecycle. (Inherited from Control.)
Load	Occurs when the server control is loaded into the Page object. (Inherited from Control.)
PageIndexChanged	Occurs when one of the pager buttons is clicked, but after the GridView control handles the paging operation.
PageIndexChanging	Occurs when one of the pager buttons is clicked, but before the GridView control handles the paging operation.
PreRender	Occurs after the Control object is loaded but prior to rendering. (Inherited from Control.)
RowCancelingEdit	Occurs when the Cancel button of a row in edit mode is clicked, but before the row exits edit mode.
RowCommand	Occurs when a button is clicked in a GridView control.
RowCreated	Occurs when a row is created in a GridView control.
RowDataBound	Occurs when a data row is bound to data in a GridView control.
RowDeleted	Occurs when a row's Delete button is clicked, but after the GridView control deletes the row.
RowDeleting	Occurs when a row's Delete button is clicked, but before the GridView control deletes the row.
RowEditing	Occurs when a row's Edit button is clicked, but before the GridView control enters edit mode.
RowUpdated	Occurs when a row's Update button is clicked, but after the GridView control updates the row.
RowUpdating	Occurs when a row's Update button is clicked, but before the GridView control updates the row.
SelectedIndexChanged	Occurs when a row's Select button is clicked, but after the GridView control handles the select operation.
SelectedIndexChanging	Occurs when a row's Select button is clicked, but before the GridView control handles the select operation.
Sorted	Occurs when the hyperlink to sort a column is clicked, but after the GridView control handles the sort operation.
Sorting	Occurs when the hyperlink to sort a column is clicked, but before the GridView control handles the sort operation.
Unload	Occurs when the server control is unloaded from memory. (Inherited from Control.)

These events are all listed in the MSDN, and here I have given a few events which are frequently used in our day to day projects:

PageIndexChanging

This event occurs when the property of the grid AllowPaging is set to true, and in the code behind the PageIndexChanging event is fired.

Paging

The DataGrid provides the means to display a group of records from the data source (for example, the first 10), and then navigates to the "page" containing the next 10 records, and so on through the data.
Paging in DataGrid is enabled by setting AllowPaging to true. When enabled, the grid will display page navigation buttons either as "next/previous" buttons or as numeric buttons. When a page navigation button is clicked, the PageIndexChanged event is thrown. It's up to the programmer to handle this event in the code.

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//AllowPaging="True"

//fires when the property AllowPaging is set to True
GridView2.PageIndex = e.NewPageIndex;
//Datasource method
TempTable();

RowCommand

The DataGrid fires the RowCommand event when any button is pressed. We can given any name as command name, and based on that, the check will be done and the loop will be executed.

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//OnRowCommand="GridView6_RowCommand"
//CommandName="view" CommandArgument='<%# Bind("id") %>'

protected void GridView6_RowCommand(object sender, GridViewCommandEventArgs e)
{
  //this will check whether the command name is equal to view. If it is
  //equal to view the it will go inside the loop.
  if (e.CommandName == "view")
  {
    //to find which row is clicked
    int row = int.Parse(e.CommandArgument.ToString());
    StringBuilder sb = new StringBuilder();
    sb.Append("<script language="'javascript'">\r\n");
    //javascript to navigate to view page.
    sb.Append(" window.open('View.aspx?id=" + row + "',
        null,'width=350,height=300,scrollbars=yes,left=350,top=200,right=5,bottom=5');");
    sb.Append("</script>");
    if (!this.IsClientScriptBlockRegistered("BindScript"))
    {
      RegisterClientScriptBlock("openScript", sb.ToString());
    }
  }
}

RowCreated

The DataGrid fires the RowCreate event when a new row is created.

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//OnRowCreated="GridView3_RowCreated" 

protected void GridView3_RowCreated(object sender, GridViewRowEventArgs e)
{
  //When a child checkbox is unchecked then the header checkbox will also be unchecked.
  if (e.Row.RowType == DataControlRowType.DataRow && (e.Row.RowState == 
    DataControlRowState.Normal || e.Row.RowState == DataControlRowState.Alternate))
  {
    CheckBox chkBxSelect = (CheckBox)e.Row.Cells[1].FindControl("chkselect");
    CheckBox chkBxHeader = (CheckBox)this.GridView3.HeaderRow.FindControl("chkHeader");
    chkBxSelect.Attributes["onclick"] = string.Format("javascript:ChildClick(
        this,'{0}');", chkBxHeader.ClientID);
  }
}

RowDeleting

The DataGrid fires the RowDeleting event when the command name is given as Delete.

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//OnRowDeleting="GridView3_RowDeleting"
//CommandName="delete"

protected void GridView3_RowDeleting(object sender, GridViewDeleteEventArgs e)
{
  //finding the row index of which row is selected.
  int row = e.RowIndex;
  //deleteing the temp row(or your delete query that will delete the row from
  //the database
  Temp.Rows[row].Delete();
  //reassigning the datasource
  GridView3.DataSource = Temp;
  GridView3.DataBind();
}

RowUpdating

The DataGrid fires the RowUpdating event when the command name is given as Update.

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//OnRowUpdating="GridView3_RowUpdating"

CommandName="update"
protected void GridView3_RowUpdating(object sender, GridViewUpdateEventArgs e)
{
  //maintaining the row index to intial position
  GridView3.EditIndex = e.RowIndex;
  //reassigning the datasource
  GridView3.DataSource = Temp;
  GridView3.DataBind();
}

RowEditing

The DataGrid fires the RowEditing event when the command name is given as Edit.

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/OnRowEditing="GridView3_RowEditing"
//CommandName="edit"

protected void GridView3_RowEditing(object sender, GridViewEditEventArgs e)
{
  //changing the index of the grid.
  GridView3.EditIndex = e.NewEditIndex - 1;
  //finding the row of the grid
  int row = e.NewEditIndex;
  //updating the rows inside the grid
  Temp.Rows[row]["name"] = ((TextBox)GridView3.Rows[e.NewEditIndex].FindControl(
      "txtname")).Text;
  Temp.Rows[row]["gender"] = ((DropDownList)GridView3.Rows[e.NewEditIndex].FindControl(
      "ddlgender")).Text;
  Temp.Rows[row]["email"] = ((TextBox)GridView3.Rows[e.NewEditIndex].FindControl(
      "txtemail")).Text;
  Temp.Rows[row]["salary"] = ((TextBox)GridView3.Rows[e.NewEditIndex].FindControl(
      "txtsalary")).Text;
  Temp.AcceptChanges();
  //total of the salary and displaying it in footer.
  Total = decimal.Parse(Temp.Compute("sum(Salary)", "Salary>=0").ToString());
  //maintaining the total value in the session
  Session["Salary"] = Total;
  //reassigning the datasource
  GridView3.DataSource = Temp;
  GridView3.DataBind();
}

RowDatabound

The DataGrid fires the RowDatabound event when a data row is bound to data in a GridView control.

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//OnRowDataBound="GridView4_RowDataBound"

protected void GridView4_RowDataBound(object sender, GridViewRowEventArgs e)
{
  //Example for grid inside a grid
  //to find the row index to the selected row.
  int index = e.Row.RowIndex;
  //check whether the row type is equal
  if (e.Row.RowType == DataControlRowType.DataRow)
  {
    //assiging datasource for the grid inside the grid.
    DataTable tempdt = new DataTable();
    tempdt.Columns.Add("Id");
    tempdt.Columns.Add("Language", typeof(String));
    DataRow dr = tempdt.NewRow();
    dr["Id"] = 1;
    dr["Language"] = "C";
    tempdt.Rows.Add(dr);
    DataRow dr1 = tempdt.NewRow();
    dr1["Id"] = 2;
    dr1["Language"] = "C++";
    tempdt.Rows.Add(dr1);
    GridView gr = (GridView)(e.Row.FindControl("GridView5"));
    if (gr != null)
    {
      gr.DataSource = tempdt;
      gr.DataBind();
    }
  }
}

Sorting

Data in a grid is commonly sorted by clicking the header of the column to sort. Sorting in a DataGrid can be enabled by setting AllowSorting to true. When enabled, the grid renders LinkButton controls in the header for each column. When the button is clicked, the grid's SortCommand event is thrown. It's up to the programmer to handle this event in the code. Because DataGrid always displays the data in the same order it occurs in the data source, the typical logic sorts the data source, and then rebinds the data to the grid.

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//AllowSorting="True"
//OnSorting="GridView2_Sorting"
//SortExpression="name"

protected void GridView2_Sorting(object sender, GridViewSortEventArgs e)
{
  //to check whether to display in ascending order or descending order
  if (e.SortExpression.Trim() == this.SortField)
    this.SortDirection = (this.SortDirection == "D" ? "A" : "D");
  else
    this.SortDirection = "A";
  this.SortField = e.SortExpression;
  TempTable();
}

Header and Footer of the Grid

This is a JavaScript to use when there is a necessity to check all the checkboxes in a column by checking a single checkbox in the grid header. While we are checking the grid header, all the checkboxes inside the grid will be selected, and if any child column is unchecked, then the header will also be unchecked.

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<script type="text/javascript">
var TotalChkBx;
var Counter;
window.onload = function()
{
    TotalChkBx = parseInt('<%= this.GridView3.Rows.Count %>');
    Counter = 0;
}
function SelectAll(CheckBox)
{
    var TargetBaseControl = document.getElementById('<%= this.GridView3.ClientID %>');
    var TargetChildControl = "chkselect";
    var Inputs = TargetBaseControl.getElementsByTagName("input");
    for(var n = 0; n < Inputs.length; ++n)
    if(Inputs[n].type == 'checkbox' && Inputs[n].id.indexOf(TargetChildControl,0) >= 0)
    Inputs[n].checked = CheckBox.checked;
    Counter = CheckBox.checked ? TotalChkBx : 0;
}
function ChildClick(CheckBox, HCheckBox)
{
    var HeaderCheckBox = document.getElementById(HCheckBox);
    if(CheckBox.checked && Counter < TotalChkBx)
    Counter++;
    else if(Counter > 0)
    Counter--;
    if(Counter < TotalChkBx)
    HeaderCheckBox.checked = false;
    else if(Counter == TotalChkBx)
    HeaderCheckBox.checked = true;
}
</script>
onclick="javascript:SelectAll(this);"

Maintaining the values in the footer is done by the following code:

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protected void GridView3_RowDataBound(object sender, GridViewRowEventArgs e)
{
  //total in the footer
  if (e.Row.RowType == DataControlRowType.Footer)
  {
    e.Row.Cells[4].Text = this.Total.ToString();
  }
}

To maintain the grid header in a fixed state, a style sheet is used in the source code:

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<style type="text/css">.DataGridFixedHeader { 
BACKGROUND: url(Images/grid_header.jpg) repeat-x; 
POSITION: relative; TOP: expression(this.offsetParent.scrollTop); HEIGHT: 27px }

</style>
<div style="width:80%; height:250px; overflow:auto;" >
<asp:GridView ID="GridView1" runat="server" 
    Width="100%" AutoGenerateColumns="False" 
    CellPadding="4" DataKeyNames="id" 
    ForeColor="#333333" GridLines="None"
    OnRowCreated="GridView1_RowCreated" 
    AllowPaging="True" AllowSorting="True"
    OnPageIndexChanging="GridView1_PageIndexChanging" OnSorting="GridView1_Sorting"
    PageSize="2" OnRowCommand="GridView1_RowCommand"
    OnRowDeleting="GridView1_RowDeleting" 
    OnRowEditing="GridView1_RowEditing">
....
....
<HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White"
    CssClass="gridHeader DataGridFixedHeader" />
.....
.....
</asp:GridView>
</div>

Export GridView to Word, Excel, and PDF

Word

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protected void btnword_Click(object sender, EventArgs e)
{
    Response.AddHeader("content-disposition", 
                       "attachment;filename=Information.doc");
    Response.Cache.SetCacheability(HttpCacheability.NoCache);
    Response.ContentType = "application/vnd.word";
    System.IO.StringWriter stringWrite = new System.IO.StringWriter();
    System.Web.UI.HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);
    // Create a form to contain the grid
    HtmlForm frm = new HtmlForm();
    GridView1.Parent.Controls.Add(frm);
    frm.Attributes["runat"] = "server";
    frm.Controls.Add(GridView1);
    frm.RenderControl(htmlWrite);
    //GridView1.RenderControl(htw);
    Response.Write(stringWrite.ToString());
    Response.End();
}

Excel

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protected void btnexcel_Click(object sender, EventArgs e)
{
    string attachment = "attachment; filename=Information.xls";
    Response.ClearContent();
    Response.AddHeader("content-disposition", attachment);
    Response.ContentType = "application/ms-excel";
    StringWriter sw = new StringWriter();
    HtmlTextWriter htw = new HtmlTextWriter(sw);
    // Create a form to contain the grid
    HtmlForm frm = new HtmlForm();
    GridView1.Parent.Controls.Add(frm);
    frm.Attributes["runat"] = "server";
    frm.Controls.Add(GridView1);
    frm.RenderControl(htw);
    //GridView1.RenderControl(htw);
    Response.Write(sw.ToString());
    Response.End();
}

PDF

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protected void btnpdf_Click(object sender, EventArgs e)
{
    Response.Clear();
    StringWriter sw = new StringWriter();
    HtmlTextWriter htw = new HtmlTextWriter(sw);
    GridView1.RenderControl(htw);
    Response.ContentType = "application/pdf";
    Response.AddHeader("content-disposition", 
             "attachment; filename=Information.pdf");
    Response.Write(sw.ToString());
    Response.End();
}

Difference between DataGrid, DataList, and Repeater

A DataGrid, DataList, and Repeater are all ASP.NET data Web controls.
They have many things in common like the DataSource property, the DataBind method, and the ItemDataBound and ItemCreated events.
When you assign the DataSource property of a DataGrid to a DataSet, each DataRow present in the DataRow collection of the DataTable is assigned to a corresponding DataGridItem, and this is the same for the rest of the two controls. But The HTML code generated for a DataGrid has an HTML TABLE <ROW> element created for the particular DataRow and it is a table form representation with columns and rows. For a DataList, it is an array of rows, and based on the template selected and the RepeatColumn property value, we can specify how many DataSource records should appear per HTML <table> row. In short, in a DataGrid, we have one record per row, but in a DataList, we can have five or six rows per row. For a Repeater control, the data records to be displayed depend upon the templates specified, and the only HTML generated is the due to the templates.
In addition to these, DataGrid has in-built support for sorting, filtering, and paging the data, which is not possible when using a DataList, and for a Repeater control, we would require to write explicit code to do paging.

Conclusion

This is my second article, and if you have any questions, you can refer to the project attached because all the code in the article is from the project. Further questions or clarifications or mistakes are welcome.