GridView columns with templatefield and adding controls at run time giving error if change .net framework from 3.5 to 4

Question

User-510697852 posted

I have added a grid view at design time,

<asp:GridView runat="server" ID="gvApplicableAnswerMulti" AutoGenerateColumns="False" RowStyle-HorizontalAlign="Center" 
EnableModelValidation="True" CellPadding="4" ForeColor="#333333" GridLines="None" Width="203px" OnInit="gvApplicableAnswerMulti_Init">

<AlternatingRowStyle BackColor="White" />
                                                       
<EditRowStyle BackColor="#2461BF" />
 <FooterStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
 <HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
 <PagerStyle BackColor="#2461BF" ForeColor="White" HorizontalAlign="Center" />
 <RowStyle BackColor="#EFF3FB" />
 <SelectedRowStyle BackColor="#D1DDF1" Font-Bold="True" ForeColor="#333333" />
</asp:GridView>

My code in gvApplicableAnswerMulti_Init, I am adding SectionName as item as one of the columns.

protected void gvApplicableAnswerMulti_Init(object sender, EventArgs e)
 {
     gvApplicableAnswerMulti.Columns.Clear();
     TemplateField tfdept = new TemplateField();
     tfdept.ItemTemplate = new GridViewTemplate(ListItemType.Item, "SectionName");
     gvApplicableAnswerMulti.Columns.Add(tfdept);
      for (int i = 0; i < ((DataTable)SessiondAnsColumns).Rows.Count; i++)
          {
             TemplateField tfchecks = new TemplateField();
             tfchecks.HeaderTemplate = new GridViewTemplate(ListItemType.Header, 
                                      ((DataTable)SessiondAnsColumns).Rows[i]["AnsOptions"].ToString());
             tfchecks.ItemTemplate = new GridViewTemplate(ListItemType.Item, "chk" + 
                                    ((DataTable)SessiondAnsColumns).Rows[i]["AnsOptions"].ToString());
                gvApplicableAnswerMulti.Columns.Add(tfchecks);

            }

        }

When i bind gvApplicableAnswerMulti to datatable,

gvApplicableAnswerMulti.DataSource = dtAnswerSections;
gvApplicableAnswerMulti.DataBind(); // this line following code executes

Following code executes,

We have GridViewPaging.cs in which GridViewTemplate calss is declared,

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:
                    
                    if (_columnName.Contains("chk"))
                    {
                        CheckBox chkColumn = new CheckBox();
                        chkColumn.ID = _columnName;
                        chkColumn.DataBinding += new EventHandler(chkColumn_DataBinding);
                        container.Controls.Add(chkColumn);
                    }
                    else
                    {
                        Label lbColumn = new Label();
                        lbColumn.ID = "lbl" + _columnName;
                        lbColumn.DataBinding += new EventHandler(lbColumn_DataBinding);
                        container.Controls.Add(lbColumn);
                    }
                    break;

                case ListItemType.EditItem:
                    break;

                case ListItemType.Footer:
                    break;
            }
        }

        /// <summary>
        /// This is the event, which will be raised when the binding happens.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        void chkColumn_DataBinding(object sender, EventArgs e)
        {
            CheckBox CBData = (CheckBox)sender;
            GridViewRow container = (GridViewRow)CBData.NamingContainer;
            object dataValue = DataBinder.Eval(container.DataItem, _columnName);
            if (dataValue != DBNull.Value)
            {
                CBData.Checked = Convert.ToBoolean(dataValue);
            }
        }

        /// <summary>
        /// This is the event, which will be raised when the binding happens.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        void lbColumn_DataBinding(object sender, EventArgs e)
        {
            Label lblData = (Label)sender;
            GridViewRow container = (GridViewRow)lblData.NamingContainer;
            object dataValue = DataBinder.Eval(container.DataItem, _columnName);
            if (dataValue != DBNull.Value)
            {
                lblData.Text = dataValue.ToString();
            }
        }
    }

For SectionName column, ITemplate.InstantiateIn() will execute and add lblColumn control will be added to each row. ID for this control will be "lblSectionName".

Then lbColumn_DataBinding() will occur and will assign text to label control.

Till this it is executing fine. 

But at later stage when i try to find lblSectionName control in gridview's row's first cell i.e.

(Label)gvApplicableAnswerMulti.Rows[0].Cells[0].FindControl("lblSectionName"); - This returns me null.

Strange this it is working fine with framework 3.5 (it won't return me null. It finds correct control lblSectionName) but if change to framework 4 it returns me null.

I can not understand what is happening. Anyone can guess?

Answer 1

User-707554951 posted

Hi hardeshis,

Based on your description, I new a project with framework 4.0

I create a WebForm1 and GridViewTemplate class.

GridViewTemplate class( completely copy the code you provided)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace WebApplication4
{
    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:

                    if (_columnName.Contains("chk"))
                    {
                        CheckBox chkColumn = new CheckBox();
                        chkColumn.ID = _columnName;
                        chkColumn.DataBinding += new EventHandler(chkColumn_DataBinding);
                        container.Controls.Add(chkColumn);
                    }
                    else
                    {
                        Label lbColumn = new Label();
                        lbColumn.ID = "lbl" + _columnName;
                        lbColumn.DataBinding += new EventHandler(lbColumn_DataBinding);
                        container.Controls.Add(lbColumn);
                    }
                    break;

                case ListItemType.EditItem:
                    break;

                case ListItemType.Footer:
                    break;
            }
        }
        void chkColumn_DataBinding(object sender, EventArgs e)
        {
            CheckBox CBData = (CheckBox)sender;
            GridViewRow container = (GridViewRow)CBData.NamingContainer;
            object dataValue = DataBinder.Eval(container.DataItem, _columnName);
            if (dataValue != DBNull.Value)
            {
                CBData.Checked = Convert.ToBoolean(dataValue);
            }
        }

        /// <summary>
        /// This is the event, which will be raised when the binding happens.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        void lbColumn_DataBinding(object sender, EventArgs e)
        {
            Label lblData = (Label)sender;
            GridViewRow container = (GridViewRow)lblData.NamingContainer;
            object dataValue = DataBinder.Eval(container.DataItem, _columnName);
            if (dataValue != DBNull.Value)
            {
                lblData.Text = dataValue.ToString();
            }
        }
    }
}

In WebForm1:

 <asp:GridView runat="server" ID="gvApplicableAnswerMulti" AutoGenerateColumns="False" RowStyle-HorizontalAlign="Center" 
EnableModelValidation="True" CellPadding="4" ForeColor="#333333" GridLines="None" Width="203px" OnInit="gvApplicableAnswerMulti_Init1">

<AlternatingRowStyle BackColor="White" />
                                                       
<EditRowStyle BackColor="#2461BF" />
 <FooterStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
 <HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
 <PagerStyle BackColor="#2461BF" ForeColor="White" HorizontalAlign="Center" />
 <RowStyle BackColor="#EFF3FB" />
 <SelectedRowStyle BackColor="#D1DDF1" Font-Bold="True" ForeColor="#333333" />
</asp:GridView>
        <asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />

CodeBehind:

 protected void Page_Load(object sender, System.EventArgs e)
        {
            DataTable dtAnswerSections = new DataTable();
            dtAnswerSections.Columns.AddRange(new DataColumn[9] {
            new DataColumn("AnsOptions", System.Type.GetType("System.String")),
             new DataColumn("SectionName", System.Type.GetType("System.String")),
              new DataColumn("chk", System.Type.GetType("System.String")),
                 new DataColumn("chkShirt", System.Type.GetType("System.String")),
                    new DataColumn("chkTrue", System.Type.GetType("System.String")),
                     new DataColumn("chkFalse", System.Type.GetType("System.String")),
                     new DataColumn("chkAnsOptions1", System.Type.GetType("System.String")),
                      new DataColumn("chkAnsOptions2", System.Type.GetType("System.String")),
                       new DataColumn("chkAnsOptions3", System.Type.GetType("System.String")),
        });
            dtAnswerSections.Rows.Add("AnsOptions1", "SectionName1", "True", "True", "True", "True", "True", "True", "True");
            dtAnswerSections.Rows.Add("AnsOptions2", "SectionName2", "False", "False", "False", "False", "True", "True");
            dtAnswerSections.Rows.Add("AnsOptions3", "SectionName3", "True", "True", "True", "True", "True", "True", "True");

            gvApplicableAnswerMulti.DataSource = dtAnswerSections;
            gvApplicableAnswerMulti.DataBind();
        }


        protected void gvApplicableAnswerMulti_Init1(object sender, EventArgs e)
        {
            DataTable dtAnswerSections = new DataTable();
            dtAnswerSections.Columns.AddRange(new DataColumn[9] {
            new DataColumn("AnsOptions", System.Type.GetType("System.String")),
             new DataColumn("SectionName", System.Type.GetType("System.String")),
              new DataColumn("chk", System.Type.GetType("System.String")),
                 new DataColumn("chkShirt", System.Type.GetType("System.String")),
                    new DataColumn("chkTrue", System.Type.GetType("System.String")),
                     new DataColumn("chkFalse", System.Type.GetType("System.String")),
                     new DataColumn("chkAnsOptions1", System.Type.GetType("System.String")),
                      new DataColumn("chkAnsOptions2", System.Type.GetType("System.String")),
                       new DataColumn("chkAnsOptions3", System.Type.GetType("System.String")),
        });
            dtAnswerSections.Rows.Add("AnsOptions1", "SectionName1", "True", "True", "True", "True", "True", "True", "True");
            dtAnswerSections.Rows.Add("AnsOptions2", "SectionName2", "False", "False", "False", "False", "True", "True");
            dtAnswerSections.Rows.Add("AnsOptions3", "SectionName3", "True", "True", "True", "True", "True", "True", "True");

            gvApplicableAnswerMulti.Columns.Clear();
            TemplateField tfdept = new TemplateField();
            tfdept.ItemTemplate = new GridViewTemplate(ListItemType.Item, "SectionName");
            gvApplicableAnswerMulti.Columns.Add(tfdept);
            for (int i = 0; i < dtAnswerSections.Rows.Count; i++)
            {
                TemplateField tfchecks = new TemplateField();
                tfchecks.HeaderTemplate = new GridViewTemplate(ListItemType.Header,
                                        dtAnswerSections.Rows[i]["AnsOptions"].ToString());
                tfchecks.ItemTemplate = new GridViewTemplate(ListItemType.Item, "chk" +
                                      dtAnswerSections.Rows[i]["AnsOptions"].ToString());
                gvApplicableAnswerMulti.Columns.Add(tfchecks);

            }
        }

        protected void Button1_Click(object sender, EventArgs e)
        {
            Label lab = (Label)gvApplicableAnswerMulti.Rows[0].Cells[0].FindControl("lblSectionName");
            Response.Write(lab.Text);
        }

Output:

Best regards 

Cathy

Answer 2

User-510697852 posted

That means it's working for you. What's wrong in my project ?? 

It's originally written under 3.5 framework. I changed to 4.0 framework without changing a single line of code. While changing anywhere i need to change any reference or anything?

Answer 3

User-707554951 posted

Hi hardeshis,

For your problem, please check the GridViewTemplate  class exited in your project after changed o framework 4.0.

Besides, I suggest you could use F12 developer tools to check if there is a label with 'lblSectionName' id existed in your page.

How you change your framework?

Please follow the correct way to do change.

https://msdn.microsoft.com/en-us/library/dd483478.aspx

https://stackoverflow.com/questions/12726225/changing-framework-from-3-5-to-4-0-at-server

Best regards

Cathy