Intermittent PageRequestManagerParserErrorException With Full Postback

I have a project with a bunch of ajaxified Telerik controls within several nested UpdatePanel controls. As part of an Excel export process, I have a button which upon clicking performs a full postback, generates a spreadsheet from a RadGrid, and finally prompts the user to download the file. 

Once in a while, though, the export process would throw the dreaded and unhelpful Sys.WebForms.PageRequestManagerParserErrorException exception.

Eilon Lipton's helpful post gave a handy checklist of things not to do, but in spite of ensuring all the common causes were accounted for, it would still occur occasionally.

I tried implementing a workaround shared by a colleague and thus far it appears to have helped. This involves setting the OnClientClicked event handler of the export button so that it triggers a brief pause prior to initiating the full postback using a client-side Javascript.

function onExportClick(sender, args)
{
     setTimeout(
          function () 
          { 
               __doPostBack(sender.id, "_MyButtonID") 
          }, 
          500
     );   
}

The error itself points you in the right direction, but some more context sure would be nice. Anyway, apparently this script mitigates situations where the Telerik controls are still in the process of being rendered when the full postback is initiated, corrupting the Response header in the process. 

LinkButton OnClick Not Firing After OnClientClick

I worked around an oddball problem where the OnClick event of an ASP LinkButton would not fire following execution of some JavaScript tied to its OnClientClick.

The intent is to enable a row in a Telerik RadGrid to be removed by clicking the corresponding button in the row, and more specifically have a modal confirmation dialog appear to prompt the user to confirm their choice.

Here's markup for the GridTemplateColumn containing the button:

<telerik:GridTemplateColumn HeaderText="Remove" UniqueName="Remove" 
  FilterControlWidth="20">
    <ItemTemplate>
        <div style="cursor: hand;">
            <asp:LinkButton runat="server" ID="_RemoveItem" 
                Name="_RemoveItem" Text=" X " Font-Underline="False" 
                ForeColor="DarkBlue" 
                OnClientClick="confirmAspButton(this, 'Are you sure?'); return false;"
                OnClick="RemoveItemButtonClick" 
                style="font-weight:bold;color:red;">
            </asp:LinkButton>
        </div>
    </ItemTemplate>
    <HeaderStyle Width="55"></HeaderStyle>
</telerik:GridTemplateColumn>

The confirmAspButton function is a little JavaScript which is bound to the OnClientClick method of the LinkButton. If the user clicks OK, the confirmation passes and a postback will occur to execute the code beneath the OnClick method, whereas if they click Cancel the dialog will simply disappear.

     function confirmAspButton(button, message) 
     {
          function aspButtonCallbackFn(arg) 
          {
             if (arg) 
             {
                  window.__doPostBack(button.name, "");
             }
          }
            
          window.radconfirm(message, aspButtonCallbackFn, 330, 120, null, "Confirm");
     }

Seems simple enough, yet for some odd reason, in Internet Explorer 10, the LinkButton brought up the dialog just fine, and although the Cancel button click performed as expected, clicking OK had the same effect as cancel and merely cleared the dialog without executing the underlying code.

I managed to find a workaround via StackOverflow which suggests using a Button rather than a LinkButton. Sure enough, this did the trick, for whatever oddball reason whose particulars I could care less to dive into...

Google-like Filtering with RadGrid and Separate Data Class

I needed to create a Google Suggest style search interface for an ASP.NET page.

Our site recently obtained licenses to the Telerik control suite, and the powerful RadGrid control looked like it was just what I needed. I found this example on the Telerik site.

Key to this setup is having a textbox for the user to input filter criteria, which is then from the user's perspective transformed into a RadComboBox object to house matching results; then once the user selects an item from the dropdown, the RadGrid is bound and displays any matching results.

I encountered a problem because our site uses a centralized class library for CRUD outside of this particular page’s code class, meaning I could not access my application’s data context from within the GridBoundColumn class definition. The Telerik example (specifically in the MyCustomFilteringColumnCS.cs file) performs its own queries as needed using a SqlDataAdapter with a ConnectionString obtained from the application configuration. A simple SELECT statement is executed which returns matching results.

When I tried to reference my centralized data class from within the GridBoundColumn class definition, I got the following error:

Cannot access non-static property … in static context.

Below is the problem code, revealing that the property CurrentUser is inaccessible to the class.

       protected void list_ItemsRequested(object o, RadComboBoxItemsRequestedEventArgs e)
     {
        // Cannot access non-static property 'CurrentUser' in static context.

        using (MyCRUD mc = new MyCRUD(CurrentUser) )
        {

              ((RadComboBox)o).DataTextField = DataField;

              ((RadComboBox)o).DataValueField = DataField;

              ((RadComboBox)o).DataSource = mc.GetMatchingAddresses(e.Text);

              ((RadComboBox)o).DataBind();

        }

     }

My GridBoundColumn class does not exist until my application instantiates it with its parent RadGrid object, so I cannot directly assign a property to it. However, I stumbled upon this post which made me realize I could, in the GridBoundColumn class definition, make several changes.

1. Define a constructor for the class which takes an existing instance of the MyCRUD class as input.

2. Create a public property in the class definition which can be assigned the MyCRUD object.

3. Create a private field in the class definition to contain the instance of the MyCRUD object to be utilized by the GridBoundColumn class.

 

Below is the modified class, with additions (*) indicated below.

       public class rgcFilterColumn : GridBoundColumn

      {   

            // * I added a constructor with an input parameter of the type 

            // * corresponding to my app’s CRUD object.       

            public rgcFilterColumn(MyCRUD mycrud)

            {

                TheDataContext = mycrud;

            }

            // * This field provides an instance of the rgcFilterColumn class 

            // * with the corresponding value set for the data context object.

            private readonly MyCRUD TheDataContext;

            // * This property enables the process which instantiates this 

            // * class to assign the MyCRUD object to TheDataContext.

            public MyCRUD thedatacontext

            {

                get { return TheDataContext; }

            }

     // RadGrid will call this method when it initializes
     // the controls inside the filtering item cells

            protected override void SetupFilterControls(TableCell cell)

            {

                base.SetupFilterControls(cell);

                cell.Controls.RemoveAt(0);

                RadComboBox combo = new RadComboBox

                {

                    ID = ("RadComboBox1" + UniqueName),

                    ShowToggleImage = false,

                    Skin = "Office2007",

                    EnableLoadOnDemand = true,

                    AutoPostBack = true,

                    MarkFirstMatch = true,

                    Height = Unit.Pixel(100)

                };

                combo.ItemsRequested += list_ItemsRequested;

                combo.SelectedIndexChanged += list_SelectedIndexChanged;

                cell.Controls.AddAt(0, combo);

                cell.Controls.RemoveAt(1);

            }

   // RadGrid will call this method when the value should
   // be set to the filtering input control(s)

           protected override void SetCurrentFilterValueToControl(TableCell cell)

           {

                base.SetCurrentFilterValueToControl(cell);

                RadComboBox combo = (RadComboBox)cell.Controls[0];

                if ((CurrentFilterValue != string.Empty))

                {

      combo.Text = CurrentFilterValue;
        }
     }

   // RadGrid will call this method when the filtering value
   // should be extracted from the filtering input control(s)

           protected override string GetCurrentFilterValueFromControl(TableCell cell)

           {

                RadComboBox combo = (RadComboBox)cell.Controls[0];

                return combo.Text;

           }

           protected void list_ItemsRequested(object o, RadComboBoxItemsRequestedEventArgs e)

           {

                // * Below we use the value of field TheDataContext to execute 

                // * a method accesible via the MyCRUD data context for the application.

                using (MyCRUD mc = TheDataContext)         

                {

                     ((RadComboBox)o).DataTextField = DataField;

                     ((RadComboBox)o).DataValueField = DataField;

                     ((RadComboBox)o).DataSource = mc.GetMatchingAddresses(e.Text);

                     ((RadComboBox)o).DataBind();

                }

           }

           private void list_SelectedIndexChanged(object o, RadComboBoxSelectedIndexChangedEventArgs e)

           {

                GridFilteringItem filterItem = (GridFilteringItem)((RadComboBox)o).NamingContainer;

                if ((UniqueName == "Index"))

                {

                    // this is filtering for integer column type

                    filterItem.FireCommandEvent("Filter", new Pair("EqualTo", UniqueName));

                }

                // filtering for string column type

                filterItem.FireCommandEvent("Filter", new Pair("Contains", UniqueName));

           }

      }

Now an instance of the GridBoundColumn class can happily utilize my application's central CRUD class for all its data retrieval operations.