ASP.Net/C# - Grid_RowDataBound - SelectedIndexChanged

 void ITemplate.InstantiateIn(System.Web.UI.Control container)
    {
        container.EnableViewState = true;
        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.

                if (_columnName == "ID")
                {
                    Label lblID = new Label();//Allocates the new text box object.
                    lblID.DataBinding += new EventHandler(lblID_DataBinding);//Attaches the data binding event
                    lblID.Width = ((Unit)200);
                    lblID.Visible = true;
                    container.Controls.Add(lblID);
                    break;
                }
                else if (_columnName == "Guid")
                {
                    Label lblGUID = new Label();
                    lblGUID.DataBinding += new EventHandler(lblGUID_DataBinding);
                    lblGUID.Width = ((Unit)200);
                    lblGUID.Visible = true;
                    container.Controls.Add(lblGUID);
                }
                else if (_columnName == "Fields")
                {
                    DropDownList ddlFields = new DropDownList();
                    ddlFields.DataBinding += new EventHandler(ddlFields_DataBinding);
                    ddlFields.Width = ((Unit)200);
                    container.Controls.Add(ddlFields);
                }
                else if (_columnName == "OperatorType")
                {
                    DropDownList ddlOperator = new DropDownList();
                    ddlOperator.DataBinding += new EventHandler(ddlOperator_DataBinding);
                    ddlOperator.Width = ((Unit)200);
                    container.Controls.Add(ddlOperator);

                }
                else if (_columnName == "EnterValue")
                {
                    TextBox txtEnterValue = new TextBox();
                    txtEnterValue.DataBinding += new EventHandler(txtEnterValue_DataBinding);
                    txtEnterValue.Width = ((Unit)100);
                    container.Controls.Add(txtEnterValue);
                }
                else if (_columnName == "Add")
                {
                    Button btnAdd = new Button();
                    btnAdd.Text = "Add";
                    btnAdd.DataBinding += new EventHandler(btnAdd_DataBinding);
                    btnAdd.Width = 50; ;
                    container.Controls.Add(btnAdd);
                }
                else if (_columnName == "Remove")
                {
                    Button btnRemove = new Button();
                    btnRemove.Text = "Remove";
                    btnRemove.DataBinding += new EventHandler(btnRemove_DataBinding);
                    btnRemove.Width = 50;
                    container.Controls.Add(btnRemove);
                }

                break;
        }
    }

   

    void txtEnterValue_DataBinding(object sender, EventArgs e)
    {
        //throw new Exception("The method or operation is not implemented.");
        TextBox txtEnterValue = (TextBox)sender;
        txtEnterValue.ID = "txtEnterValue";
        GridViewRow container = (GridViewRow)txtEnterValue.NamingContainer;

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

        if (dataValue != null)
        {
            txtEnterValue.Text = dataValue.ToString();
        }  
    }

    void ddlOperator_DataBinding(object sender, EventArgs e)
    {
        //throw new Exception("The method or operation is not implemented.");
        DropDownList ddlOperator = (DropDownList)sender;
        ddlOperator.ID = "ddlOperator";
        //ddlOperator.EnableViewState = true;
        //ddlOperator.AutoPostBack = true;
        GridViewRow container = (GridViewRow)ddlOperator.NamingContainer;
            object dataValue  = DataBinder.Eval(container.DataItem, _columnName);

            if (dataValue != null)
            {
                ddlOperator.DataSource = dataValue;
                ddlOperator.DataValueField = "ID";
                ddlOperator.DataTextField = "Description";
            }

    }

    void ddlFields_DataBinding(object sender, EventArgs e)
    {
        //throw new Exception("The method or operation is not implemented.");

        DropDownList ddlFields = (DropDownList)sender;
        ddlFields.ID = "ddlFields";
        ddlFields.SelectedIndexChanged += new EventHandler(ddlFields_SelectedIndexChanged);
       
        ddlFields.EnableViewState = true;
        ddlFields.AutoPostBack = true;
        
        GridViewRow container = (GridViewRow)ddlFields.NamingContainer;
        object dataValue = DataBinder.Eval(container.DataItem, _columnName);

        if (dataValue != null)
        {
            ddlFields.DataSource = dataValue;
            ddlFields.DataValueField = "SuperType";
            ddlFields.DataTextField = "FieldName";
        }
    }

    void ddlFields_SelectedIndexChanged(object sender, EventArgs e)
    {
        //throw new NotImplementedException();


    }

  
    void lblGUID_DataBinding(object sender, EventArgs e)
    {
        //throw new Exception("The method or operation is not implemented.");

        Label lblGUID = (Label)sender;
        lblGUID.ID = "GUID";
        lblGUID.Visible = true;
        GridViewRow container = (GridViewRow)lblGUID.NamingContainer;

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

        if (dataValue != DBNull.Value)
        {
            lblGUID.Text = dataValue.ToString();
        }
    }

    void lblID_DataBinding(object sender, EventArgs e)
    {
        //throw new Exception("The method or operation is not implemented.");
        Label lblID = (Label)sender;
        lblID.ID = "ID";
        lblID.Visible = true;
        GridViewRow container = (GridViewRow)lblID.NamingContainer;

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

        if (dataValue != DBNull.Value)
        {
            lblID.Text = dataValue.ToString();
        }
    }

    void btnAdd_DataBinding(object sender, EventArgs e)
    {
        //throw new Exception("The method or operation is not implemented.");
        Button btnAdd = (Button)sender;
        GridViewRow container = (GridViewRow)btnAdd.NamingContainer;

        btnAdd.ID = "btnAdd";
        btnAdd.CommandName = "Add";
        btnAdd.CommandArgument = container.DataItemIndex.ToString();
        object dataValue = DataBinder.Eval(container.DataItem, _columnName);

        if (dataValue != DBNull.Value)
        {
            btnAdd.Text = dataValue.ToString();
        }
    }

    void btnRemove_DataBinding(object sender, EventArgs e)
    {
        //throw new Exception("The method or operation is not implemented.");
        Button btnRemove = (Button)sender;
        GridViewRow container = (GridViewRow)btnRemove.NamingContainer;

        btnRemove.ID = "btnRemove";
        btnRemove.CommandName = "Remove";
        btnRemove.CommandArgument = container.DataItemIndex.ToString();

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

        if (dataValue != null)
        {
            btnRemove.Text = dataValue.ToString();
        }

        if (container.DataItemIndex > 0)
        {
            btnRemove.Enabled = true;
        }
        else
        {
            btnRemove.Enabled = false;
        
        }

    }