Unable to change background of multiple rows in ListView using ItemDataBound?

Question

i have a ListView in the updatePanel

     <ItemTemplate >
            <table id="TestTable" runat="server">
              <tr id="TestRow" runat="server">
                <td id="TestData" runat="server">

                 Name:
                 <asp:Label ID="Label1" runat="server" Text='<%# Eval("Name") %>' />
                  <br />
                  UserID:
                  <asp:Label ID="Label2" runat="server" Text='<%# Eval("UserID") %>' />
                  <br />
                  DateAndTime:
                 <asp:Label ID="Label3" runat="server" Text='<%# Eval("DateAndTime")%>' />

                </td>
               </tr>
              </table>
     </ItemTemplate>

i used the below code to change the Background of the table according to database value

protected void ListViewFlowTable_ItemDataBound(object sender, ListViewItemEventArgs e)
        {
            if(e.Item.ItemType == ListViewItemType.DataItem)
            {
                ListViewDataItem ItemToDisplay = (ListViewDataItem)e.Item;
                string UserId = DataBinder.Eval(ItemToDisplay.DataItem, "UserID").ToString();
                if(UserId == "1")
                {
                    HtmlTableCell newRow = (HtmlTableCell)e.Item.FindControl("TestData");
                    newRow.BgColor = "Yellow";
                }
                else if(UserId == "2")
                {
                    HtmlTableCell newRow = (HtmlTableCell)e.Item.FindControl("TestData");
                    newRow.BgColor = "Green";
                }
            }
        }

UserID 2 has multiple posts, so it is giving the below error, UserID 1 has only one post and the color is changed to that row as expected.

System.NullReferenceException was unhandled by user code
  HResult=-2147467261
  Message=Object reference not set to an instance of an object.
  Source=Dream

newRow is null (Nothing). The code one line 269 isn't producing a value. — Brandon, Jan 06 '14 at 17:16
I'm not sure, I'm not very familiar with ASP.NET. You'll want to actually have a look at what `e` produces when it gets into that function. It's most-likely not able to find "TestRow". I agree with @paqogomez though. This is probably a duplicate. — Brandon, Jan 06 '14 at 17:23

score 1 · Answer 1 · edited May 23 '17 at 12:28

1

You have a NullReference exception because you're trying to find a control that doesn't exist. Indeed, in the e.Item you don't have a HtmlTable object but instead you expect a HtmlTableRow.

You should review the cast in the line 269, modifying it, from HtmlTable to HtmlTableRow:

ListViewDataItem ItemToDisplay = (ListViewDataItem)e.Item;
int UserId = (int)DataBinder.Eval(ItemToDisplay.DataItem, "UserID");
if(UserId == 1)
{
   HtmlTableRow newRow = (HtmlTableRow)e.Item.FindControl("TestRow");
   newRow.BgColor = "Yellow";
}

As advice (I don't know if you have always results to display in your ListView), check always if you have Null objects, like suggested here.

UPDATE

I tested your code in a sample ASP.NET web application and it works properly. I think then the problem could be how you're loading data into the ListView. Can you post the code you wrote to load data into the ListView control?

edited May 23 '17 at 12:28

Community

1
1

answered Jan 06 '14 at 17:39

Alberto Solano

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@GeneliaD'Souza Have you fixed your issue? – Alberto Solano Jan 07 '14 at 08:43
@GeneliaD'Souza In the ItemTemplate you define the structure of each row of a table that will be shown in the listView. Furthermore, in the question that you linked, there's no but . I updated my answer.
– Alberto Solano Jan 10 '14 at 11:04
please dont read the question i linked, only check my question.i tried to find the control form UpdatePanel and also ListView controls,what am i doing is checking the userid of that data in that row and according to the id i want to change the row background,please check if my code is wrong. – Genelia D'Souza Jan 10 '14 at 11:17
@GeneliaD'Souza I checked the code in a sample web application and it works (I used few simple data loading lines of code). Can you post the code you wrote to load data into the ListView control? – Alberto Solano Jan 10 '14 at 11:40
@GeneliaD'Souza Thank you. Your data source code seems correct. Are you sure that all the parameters involved in the LINQ search and in the binded collection are not null? – Alberto Solano Jan 10 '14 at 11:57
when i remove OnItemDataBound the listview works fine – Genelia D'Souza Jan 10 '14 at 12:16
@GeneliaD'Souza Okay, understood. I don't have any other idea. Yes, removing the event the listview works fine because the exception was thrown there, and without the method there's no exception to throw. Unfortunately, I don't know other alternatives for `ListViewDataItem ItemToDisplay = (ListViewDataItem)e.Item; int UserId = (int)DataBinder.Eval(ItemToDisplay.DataItem, "UserID");` and `HtmlTableRow newRow = (HtmlTableRow)e.Item.FindControl("TestRow");`. Sorry! Check again the object `HtmlTable newRow` is still null or not. – Alberto Solano Jan 10 '14 at 14:05
Please check the question, it is changed, iam getting new type of errors now – Genelia D'Souza Jan 11 '14 at 05:20
@GeneliaD'Souza You have that exception maybe because there's something related to `UserID == 2` that is null. Debug and check the data you're using for each user. – Alberto Solano Jan 13 '14 at 08:47
Thanks,but i got the answer at forums.asp.net and i cant answer here because of some people marked it as duplicate . – Genelia D'Souza Jan 14 '14 at 08:25
@GeneliaD'Souza Ah, good for you. Which was the problem? It was a null property related to UserID? – Alberto Solano Jan 14 '14 at 08:39
since i was new to this itemdatabound event, i didnt know that Alternate template was problem. it was unable to find the table because alternate was displaying table with different id. – Genelia D'Souza Jan 14 '14 at 14:43

score 0 · Answer 2 · answered Jan 06 '14 at 17:23

0

Your line:

  HtmlTable newRow = (HtmlTable)e.Item.FindControl("TestRow");

Is not finding that control, hence you get a NullRef error on newRow.

answered Jan 06 '14 at 17:23

T McKeown

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1
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Now, if you could tell him why its not finding the control, this would be an answer. – crthompson Jan 06 '14 at 17:24
My listView control is in UpdatPanel, is that what causing the problem ? – Genelia D'Souza Jan 06 '14 at 17:25
i think i can actually... – T McKeown Jan 06 '14 at 17:25
@TMcKeown Please help solving the problem – Genelia D'Souza Jan 06 '14 at 17:27
@GeneliaD'Souza, is your ItemTemplate for every row? Wouldn't you end up having MANY TestRow tables? – T McKeown Jan 06 '14 at 17:28
wouldn't it be easier to grab the zero indexed control of the Controls collection for each item? You know it will be the table yes? – T McKeown Jan 06 '14 at 17:32
can you twll me how to do that @TMcKeown – Genelia D'Souza Jan 11 '14 at 12:39

Unable to change background of multiple rows in ListView using ItemDataBound?

2 Answers2