Problem adding dynamic columns to an ASP.NET Gridview

Question

I'm having a problem dynamically adding columns to a GridView. I need to change the layout -- i.e. the included columns -- based on the value in a DropDownList. When the user changes the selection in this list, I need to remove all but the first column and dynamically add additional columns based on the selection.

I have only one column defined in my markup -- column 0, a template column, in which I declare a Select link and another application specific LinkButton. That column needs to always be there. When the ListBoxSelection is made, I remove all but the first column and then re-add the desired columns (in this sample, I've simplified it to always add a "Title" column). Here is a portion of the code:

RemoveVariableColumnsFromGrid();
BoundField b = new BoundField();
b.DataField = "Title";
this.gvPrimaryListView.Columns.Add(b);
this.gvPrimaryListView.DataBind();


private void RemoveVariableColumnsFromGrid() {
    int ColCount = this.gvPrimaryListView.Columns.Count;
    //Leave column 0 -- our select and view template column
    while (ColCount > 1) {
        this.gvPrimaryListView.Columns.RemoveAt(ColCount - 1);
        --ColCount;
    }
}

The first time this code runs through, I see both the static column and the dynamically added "Title" column. However, the next time a selection is made, the first column is generated empty (nothing in it). I see the title column, and I see the first column to its left -- but there's nothing generated within it. In the debugger, I can see that gvPrimaryListView does indeed still have two columns and the first one (index 0) is indeed a template column. In fact, the column even retains it's width which is set as 165px in the markup below (for debugging purposes).

Any ideas? TIA.

<asp:GridView ID="gvPrimaryListView" runat="server" Width="100%" AutoGenerateColumns="false"
    DataKeyNames="Document_ID" EnableViewState="true" DataSourceID="odsPrimaryDataSource"
    AllowPaging="true" AllowSorting="true" PageSize="10" OnPageIndexChanging="activeListView_PageIndexChanging"
    AutoGenerateSelectButton="False" OnSelectedIndexChanged="activeListView_SelectedIndexChanged"
    Visible="true" OnRowDataBound="CtlDocList_RowDataBound" Font-Size="8pt" Font-Names="Helvetica">
    <Columns>
        <asp:TemplateField ShowHeader="false">
            <ItemTemplate>
                <asp:LinkButton EnableTheming="false" ID="CtlSelectDocRowBtn" runat="server" Text="Select"
                    CommandName="Select" CssClass="gridbutton" OnClick="RowSelectBtn_Click" />
                <asp:ImageButton EnableTheming="false" ID="DocViewBtn" runat="server" ImageUrl="../../images/ViewDoc3.png"
                    CssClass="gridbutton" CommandName="Select" OnClick="DocViewBtn_Click" />
            </ItemTemplate>
            <ItemStyle Width="165px" />
        </asp:TemplateField>
    </Columns>
    <EmptyDataTemplate>
        <asp:Label ID="Label6" runat="server" Text="No rows found." SkinID="LabelHeader"></asp:Label>
    </EmptyDataTemplate>
</asp:GridView>

Answer 1

Just some additional information.

It has nothing to do with the fact that it is the first column but everything to do with the fact that it is a TemplateField. If I put a normal column to the left (in the markup) and shift the TemplateField column to the right, the first column renders fine, and the (now second) TemplateField column disappears.

Another strange thing -- the problem doesn't happen the first postback -- OR THE SECOND -- but it starts on the third postback and then continues for subsequent postbacks. I'm stumped.

Answer 2

I found this little nugget in the documentation, under the DataControlFieldCollection Class.

If you are using the GridView or DetailsView control, the DataControlField objects that are automatically created (for example, when the AutoGenerateColumns property is true) are not stored in the publicly accessible fields collection. You can only access and manipulate DataControlField objects that are not automatically generated.

I guess the answer is to do all of your column manipulation in code, and then your approach should work fine.

Answer 3

Thanks Ken. But I actually have set AutoGenerateSelectButton and AutoGenerateColumns to false. The template field is created in the markup (it looks like creating one in code is very tough). Note that that since the field is not auto-generated, it is available in the Columns collection (I see it in the debugger).

Answer 4

Instead of dynamically adding columns, could you define them at the outset and hide/show them as needed (either with Visible="false" or setting the CssClass of the control/header/footer to a class with "display: none;")? I use this method in some of my code, including template columns, with no issues.

Answer 5

Sorry, Decker. I missed a few key points obviously.. :)

If this is still a problem for you, I wonder if it makes a difference what you have in your item template? If you just put some text in there, then refresh the page a few times, does the text appear on the first load, then not on the second?

Also, when the problem arises is there any html markup at all in the cells or are they completely empty?

Answer 6

I recently conquered silmilar issues with dynamic columns in gridviews, perhaps this will help.

First turn the viewstate off
Second add the columns programatically in a function fired in the oninit event
Lastly I used the following helper class to cause the checkboxes to instantiate when the RowDataBound event kicked off. Yes some of it is hard coded.

Heck here is all the code. Have at it :) Warrenty as is, blah blah blah...

Finally since I am just getting my feet wet DotNet any tips would be appreciated [IE don't rip me too much :) ]. And yes 'borrowed' the initial code from the web somewhere, sorry I cant remember off the top of my head :(

-- Fire this off in protected override void OnInit

 private void GridViewProject_AddColumns()
 {
  DataSet dsDataSet = new DataSet();
  TemplateField templateField = null;

  try
  {
   StoredProcedure sp = new StoredProcedure("ExpenseReportItemType_GetList", "INTRANETWEBDB", Context.User.Identity.Name);
   dsDataSet = sp.GetDataSet();

   if (sp.RC != 0 && sp.RC != 3000)
   {
    labelMessage.Text = sp.ErrorMessage;
   }

   int iIndex = 0;
   int iCount = dsDataSet.Tables[0].Rows.Count;
   string strCategoryID = "";
   string strCategoryName = "";
   iStaticColumnCount = GridViewProject.Columns.Count;

   // Insert all columns immediatly to the left of the LAST column
   while (iIndex < iCount)
   {
    strCategoryName = dsDataSet.Tables[0].Rows[iIndex]["CategoryName"].ToString();
    strCategoryID = dsDataSet.Tables[0].Rows[iIndex]["CategoryID"].ToString();

    templateField = new TemplateField();
    templateField.HeaderTemplate = new GridViewTemplateExternal(DataControlRowType.Header, strCategoryName, strCategoryID);
    templateField.ItemTemplate = new GridViewTemplateExternal(DataControlRowType.DataRow, strCategoryName, strCategoryID);
    templateField.FooterTemplate = new GridViewTemplateExternal(DataControlRowType.Footer, strCategoryName, strCategoryID);

    // Have to decriment iStaticColumnCount to insert dynamic columns BEFORE the edit row
    GridViewProject.Columns.Insert((iIndex + (iStaticColumnCount-1)), templateField);
    iIndex++;
   }
   iFinalColumnCount = GridViewProject.Columns.Count;
   iERPEditColumnIndex = (iFinalColumnCount - 1); // iIndex is zero based, Count is not
  }
  catch (Exception exception)
  {
   labelMessage.Text = exception.Message;
  }
 }

-- Helper Class

public class GridViewTemplateExternal : System.Web.UI.ITemplate
{
 #region Fields
 public DataControlRowType DataRowType;
 private string strCategoryID;
 private string strColumnName;
 #endregion

 #region Constructor
 public GridViewTemplateExternal(DataControlRowType type, string ColumnName, string CategoryID)
 {
  DataRowType = type; // Header, DataRow,
  strColumnName = ColumnName; // Header name
  strCategoryID = CategoryID;
 }
 #endregion

 #region Methods
 public void InstantiateIn(System.Web.UI.Control container)
 {
  switch (DataRowType)
  {
   case DataControlRowType.Header:
    // build the header for this column
    Label labelHeader = new Label();
    labelHeader.Text = "<b>" + strColumnName + "</b>";
    // All CheckBoxes "Look Up" to the header row for this information
    labelHeader.Attributes["ERICategoryID"] = strCategoryID;
    labelHeader.Style["writing-mode"] = "tb-rl";
    labelHeader.Style["filter"] = "flipv fliph";
    container.Controls.Add(labelHeader);
    break;
   case DataControlRowType.DataRow:
    CheckBox checkboxAllowedRow = new CheckBox();
    checkboxAllowedRow.Enabled = false;
    checkboxAllowedRow.DataBinding += new EventHandler(this.CheckBox_DataBinding);
    container.Controls.Add(checkboxAllowedRow);
    break;
   case DataControlRowType.Footer:
    // No data handling for the footer addition row
    CheckBox checkboxAllowedFooter = new CheckBox();
    container.Controls.Add(checkboxAllowedFooter);
    break;
   default:
    break;
  }
 }
 public void CheckBox_DataBinding(Object sender, EventArgs e)
 {
  CheckBox checkboxAllowed = (CheckBox)sender;// get the control that raised this event
  GridViewRow row = (GridViewRow)checkboxAllowed.NamingContainer;// get the containing row
  string RawValue = DataBinder.Eval(row.DataItem, strColumnName).ToString();
  if (RawValue.ToUpper() == "TRUE")
  {
   checkboxAllowed.Checked = true;
  }
  else
  {
   checkboxAllowed.Checked = false;
  }
 }
 #endregion
}

Answer 7

diningphilanderer.myopenid.com has a similar approach to what I would recommend.

The problem is that you have to rebind the grid each time a postback occurs and consequently you have to rebuild the columns. I like to have a method called BindGrid() that first clears the Columns GridView1.Columns.Clear(); then adds them programatically, then sets the datasource and calls databind. Make sure you have viewstate disabled for the grid and you have autogeneratecolumns = false;

Answer 8

I found this earlier today: TemplateField in a GridView doesn't have its ViewState restored when BoundFields are inserted.

Looks like a bug that Microsoft doesn't plan on fixing, so you'll have to try one of the solutions above. I'm having the same problem -- I have some DataBoundFields and some TemplateFields, and after a postback, the TemplateField based columns lose their controls and data.