DataGrid.PageIndexChanged not firing on when 0th page requested

Discussion in 'ASP .Net Datagrid Control' started by Marc Woolfson, May 23, 2007.

  1. Hello,

    I have a Web Part that contains a relatively simple DataGrid, paginated
    across four pages. Switching between pages 2, 3 and 4 works fine, but if you
    request the first (0th) page again, the PageIndexChanged event does not fire.
    Please see my code below:

    1 public class ListOfDataWebPart : WebPart
    2 {
    3
    4 protected DataGrid TestDataGrid;
    5 protected DataSet pt_dgData;
    6
    7 /// <summary>
    8 /// Prepare data to display in the datagrid on first page request
    9 /// </summary>
    10 /// <param name="e"></param>
    11 protected override void OnLoad(EventArgs e)
    12 {
    13 base.OnLoad(e);
    14
    15 if (!this.Page.IsPostBack)
    16 {
    17 pt_dgData = GetDataSource();
    18 ViewState["dgData"] = pt_dgData;
    19 }
    20 }
    21
    22 /// <summary>
    23 /// Render the web part, and controls contained therein
    24 /// </summary>
    25 /// <param name="writer"></param>
    26 protected override void Render(System.Web.UI.HtmlTextWriter
    writer)
    27 {
    28 this.Title = "List of Data";
    29 this.AllowClose = false;
    30 this.AllowMinimize = false;
    31 this.AllowEdit = false;
    32
    33 TestDataGrid.RenderControl(writer);
    34
    35 writer.Write("Current page shown in grid: " +
    TestDataGrid.CurrentPageIndex);
    36 }
    37
    38 /// <summary>
    39 /// Add additional controls to the web part
    40 /// </summary>
    41 protected override void CreateChildControls()
    42 {
    43 GetDataGrid();
    44
    45 base.CreateChildControls();
    46 }
    47
    48 /// <summary>
    49 /// Create, populate, event handle and stylise the datagrid
    control
    50 /// </summary>
    51 private void GetDataGrid()
    52 {
    53 // core grid
    54 TestDataGrid = new DataGrid();
    55 TestDataGrid.ID = "TestDG";
    56 TestDataGrid.AllowPaging = true;
    57 TestDataGrid.PageSize = 5;
    58 TestDataGrid.PagerStyle.Mode = PagerMode.NumericPages;
    59 TestDataGrid.AutoGenerateColumns = false;
    60 TestDataGrid.EnableViewState = true;
    61
    62 // styles
    63 TestDataGrid.CellPadding = 1;
    64 TestDataGrid.GridLines = GridLines.None;
    65 TestDataGrid.Width = new Unit(100, UnitType.Percentage);
    66 TestDataGrid.ItemStyle.CssClass = "ms-vb2";
    67 TestDataGrid.AlternatingItemStyle.CssClass =
    "ms-alternating ms-vb2";
    68 TestDataGrid.HeaderStyle.CssClass = "ms-vh2-nofilter";
    69 TestDataGrid.PagerStyle.CssClass = "ms-menutoolbar
    ms-toolbar";
    70 TestDataGrid.PagerStyle.HorizontalAlign =
    HorizontalAlign.Right;
    71
    72 // events
    73 TestDataGrid.PageIndexChanged += new
    DataGridPageChangedEventHandler(TestDataGrid_PageIndexChanged);
    74
    75 // columns
    76 BoundColumn l_idCol = new BoundColumn();
    77 l_idCol.HeaderText = "ID";
    78 l_idCol.DataField = "ID";
    79 TestDataGrid.Columns.Add(l_idCol);
    80
    81 BoundColumn l_ValueCol = new BoundColumn();
    82 l_ValueCol.HeaderText = "Value";
    83 l_ValueCol.DataField = "Value";
    84 TestDataGrid.Columns.Add(l_ValueCol);
    85
    86 // rendering
    87 RebindDG();
    88 this.Controls.Add(TestDataGrid);
    89 }
    90
    91 /// <summary>
    92 /// Change the page displayed within the datagrid control
    (seemingly fails to execute when 0th page requested)
    93 /// </summary>
    94 /// <param name="source"></param>
    95 /// <param name="e"></param>
    96 protected void TestDataGrid_PageIndexChanged(Object source,
    DataGridPageChangedEventArgs e)
    97 {
    98 this.Page.Response.Write("New page requested from grid: " +
    e.NewPageIndex);
    99 TestDataGrid.CurrentPageIndex = e.NewPageIndex;
    100 RebindDG();
    101 }
    102
    103 /// <summary>
    104 /// Rebind the datagrid to the data held in ViewState
    105 /// </summary>
    106 private void RebindDG()
    107 {
    108 pt_dgData = (DataSet)ViewState["dgData"];
    109
    110 TestDataGrid.DataSource = pt_dgData;
    111 TestDataGrid.DataBind();
    112 }
    113
    114 /// <summary>
    115 /// Create a dummy dataset to test the control
    116 /// </summary>
    117 /// <returns>The DataSet to bind to the grid</returns>
    118 private DataSet GetDataSource()
    119 {
    120 DataSet l_ds = new DataSet();
    121 DataTable l_dt = new DataTable();
    122 DataRow l_row;
    123
    124 l_dt.Columns.Add("ID", typeof(int));
    125 l_dt.Columns.Add("Value", typeof(string));
    126
    127 // create 20 entries with the row number in the ID column
    and a random string in the Value column
    128 for (int i = 0; i < 20; i++)
    129 {
    130 l_row = l_dt.NewRow();
    131 l_row[0] = i;
    132 l_row[1] = Guid.NewGuid().ToString();
    133 l_dt.Rows.Add(l_row);
    134 }
    135 l_ds.Tables.Add(l_dt);
    136
    137 return l_ds;
    138 }
    139
    140 }

    Writing the values back to the screen show that when the nth page is
    requested the messages show the correct values, but the 0th page only shows
    the current page number, not the requested one as well.

    I have seen a few articles on problems with this event not firing at all,
    but this doesn't seem to be my issue. The one post I found that seemed to
    match this problem didn't have a reply :'( . Does anyone have any pointers?

    Thanks,

    Marc
     
    Marc Woolfson, May 23, 2007
    #1
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  2. I swear this question came up 3 weeks ago - there about. Have a google in
    here for the solution.

    --
    Regards,
    Alvin Bruney
    ------------------------------------------------------
    Shameless author plug
    Excel Services for .NET is coming...
    https://www.microsoft.com/MSPress/books/10933.aspx
    OWC Black Book www.lulu.com/owc
    Professional VSTO 2005 - Wrox/Wiley


     
    Alvin Bruney [MVP], May 24, 2007
    #2
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  3. Hi Alvin,

    I think I found the post you are referring to
    (http://groups.google.co.uk/group/mi...read/thread/5d2d46c629871c9a/d0e60f550ec24b09)
    but the original poster wasn't very generous in explaining the resolution,
    and neither have other people
    (http://groups.google.co.uk/group/mi...read/thread/a1038800585554d2/86d7d023a8b58a1c).
    Another old post
    (http://groups.google.co.uk/group/mi...b992a15f201/ccce5ffc1396079e#ccce5ffc1396079e)
    had a similar issue but this was resolved by setting ViewState = true on the
    DataGrid. Mine already has this setting.

    The more I look at this, the more it seems that I am creating and binding
    the dynamic control at the wrong stage in the ASP.NET life cycle. I have
    tried putting trace messages everywhere and analysing the results, and it
    seems that, as the last post above, the DataGrid gets recreated *twice* upon
    most Postbacks. Should its creation be moved out of the CreateChildControls()
    method and into (e.g.) the OnInit()?

    Thanks,

    Marc
     
    Marc Woolfson, May 24, 2007
    #3
  4. Hi again,

    I found one post which resolved a similar issue by databinding the grid in
    the PreRender event. I tried this, which seemed to fix the '0th page'
    problem.

    I still have an issue with multiple databinding upon postbacks which now
    seems to be preventing my Command event from firing - or more precisely,
    reporting it as firing in the trace - and having an effect on the rendered
    grid. I also have a SortCommand event which as well as sorting the data
    writes a value to ViewState. This is definitely getting executed as that
    particular value is changing, but the grid is seemingly only sorting
    correctly on the second databind, so the trace doesn't even show evidence of
    the SortCommand itself being fired.

    It would be great if MS provided an example of DataGrids as dynamic controls
    with all relevant events/GUI controls working as desired...
     
    Marc Woolfson, May 24, 2007
    #4
  5. Marc Woolfson

    Scott M. Guest

    Make sure that on the first page_load, you are calling the grid's databind
    method. But, on subsequent loads, it should NOT be in Page_Load, but
    instead have it in the various eventhandlers for your gird
    (PageIndexChanged, EditCommand, DeleteCommand, UpdateCommand, SortCommand,
    etc.).


     
    Scott M., May 25, 2007
    #5
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