How to create template columns dynamically in a grid view

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Sample Image - DynamicColumnsWithTemplate.jpg

Introduction

This article describes about how to create template columns dynamically in a grid view.

Many times we have the requirement where we have to create columns dynamically. This article describes you about the dynamic loading of data using the DataTable as the datasource.

Let’s have a look at the code to understand better.

Create a gridview in the page,

Drag and drop the GridView on to the page

Manually type GridView definition in the page.

<tr>

<td>

<strong>Dynamic Grid with Template Column</strong></td>

</tr>

<tr>

<td>

<asp:GridView ID="GrdDynamic" runat="server" AutoGenerateColumns="False">

</Columns>

</asp:GridView>

</td>

</tr>

</table>

With this we are done with creating a GridView in the page.

Let’s move on to the code-beside to understand the background history of the page.

Here I am describing about, how to create template columns.

//Iterate through the columns of the datatable to set the data bound field dynamically.

foreach (DataColumn col in dt.Columns)

{

//Declare the bound field and allocate memory for the bound field.

TemplateField bfield = new TemplateField();

//Initalize the DataField value.

bfield.HeaderTemplate = new GridViewTemplate(ListItemType.Header, col.ColumnName);

//Initialize the HeaderText field value.

bfield.ItemTemplate = new GridViewTemplate(ListItemType.Item, col.ColumnName);

//Add the newly created bound field to the GridView.

GrdDynamic.Columns.Add(bfield);

}

//Initialize the DataSource

GrdDynamic.DataSource = dt;

//Bind the datatable with the GridView.

GrdDynamic.DataBind();

Let’s start dissecting right from the top,

Create a DataTable which will hold the table definition and data for the GridView. This table is used as a DataSource for the GridView.
DataTable dt = new DataTable();
Once the DataTable is created, let’s add 2 columns, ID & Name to the DataTable.
The logic behind creating dynamic column starts by creating a TemplateField instance.
Once the TemplateField is created, I am initializing the HeaderTemplate and ItemTemplate with the newly created GridViewTemplate.We will come back to the GridViewTemplate again.
Once the creation of the dynamic columns is completed, I am assigning the DataSource of the GridView and call the DataBind method to load the GridView with data dynamically.

Let’s come back to the interesting part of the template columns i.e class GridViewTemplate.

//A customized class for displaying the Template Column

public class GridViewTemplate : ITemplate

{

//A variable to hold the type of ListItemType.

ListItemType _templateType;

//A variable to hold the column name.

string _columnName;

//Constructor where we define the template type and column name.

public GridViewTemplate(ListItemType type, string colname)

{

//Stores the template type.

_templateType = type;

//Stores the column name.

_columnName = colname;

}

void ITemplate.InstantiateIn(System.Web.UI.Control container)

{

switch (_templateType)

{

case ListItemType.Header:

//Creates a new label control and add it to the container.

Label lbl = new Label(); //Allocates the new label object.

lbl.Text = _columnName; //Assigns the name of the column in the lable.

container.Controls.Add(lbl); //Adds the newly created label control to the container.

break;

case ListItemType.Item:

//Creates a new text box control and add it to the container.

TextBox tb1 = new TextBox(); //Allocates the new text box object.

tb1.DataBinding += new EventHandler(tb1_DataBinding); //Attaches the data binding event.

tb1.Columns = 4; //Creates a column with size 4.

container.Controls.Add(tb1); //Adds the newly created textbox to the container.

break;

case ListItemType.EditItem:

//As, I am not using any EditItem, I didnot added any code here.

break;

case ListItemType.Footer:

CheckBox chkColumn = new CheckBox();

chkColumn.ID = "Chk" + _columnName;

container.Controls.Add(chkColumn);

break;

}

/// <summary>

/// This is the event, which will be raised when the binding happens.

/// </summary>

/// <param name="sender"></param>

/// <param name="e"></param>

void tb1_DataBinding(object sender, EventArgs e)

{

TextBox txtdata = (TextBox)sender;

GridViewRow container = (GridViewRow)txtdata.NamingContainer;

object dataValue = DataBinder.Eval(container.DataItem, _columnName);

if (dataValue != DBNull.Value)

{

txtdata.Text = dataValue.ToString();

}

Any class that should be used as a template should be inherited from the ITemplate class.

ITemplate defines the behavior for populating a templated ASP.NET server control with child controls. The child controls represent the inline templates defined on the page.

One of the interesting method in the ITemplate class is InstantiateIn(Control Container),which defines the Control object that child controls and templates belong to. These child controls are in turn defined within an inline template.

In the InstanceIn method, based on the _templateType selected, I am creating the necessary controls.

That’s all your dynamic GridView is ready. I hope this information would be helpful.

There is another interesting scenario, I would like to bring forward. i.e let’s assume that we have added a button control to the page. Upon user clicking on the button control, the page gets post back. Once the page postback, and if we don’t create the template column again upon post back, the controls would disappear. This is one of the drawbacks of this approach.

Enjoy programming.