ListView can't find control in edit item template

Question

User646364117 posted

My problem is that I have a dropdown list in a ListView. When I go into Edit it is changing from its selected value.

I am trying to get the proper value from the database and rebind the dropdownlist.

I can't find the hidden field that holds the selected value. Get error

Object reference not set to an instance of an object 

Dim hfTempID As HiddenField = CType(LvTemplate.EditItem.FindControl("hfTempID"), HiddenField)

My code is

    Private Sub LvTemplate_ItemEditing(sender As Object, e As ListViewEditEventArgs) Handles LvTemplate.ItemEditing
        Dim TempID As Integer
        Dim catid As Integer
        Dim hfTempID As HiddenField = CType(LvTemplate.EditItem.FindControl("hfTempID"), HiddenField)
        TempID = Convert.ToInt16(hfTempID.Value)
        catid = GetCategoryIDForTemplate(TempID)
        'Get selected category from db and populate ddl
        Dim ddlCategoryEdit As DropDownList = CType(LvTemplate.EditItem.FindControl("ddlCategoryEdit"), DropDownList)
        ddlCategoryEdit.SelectedValue = catid

        LvTemplate.EditIndex = e.NewEditIndex
        BindLvTemplate()
        BindGvCategoryTemplate()
    End Sub

My markup is

<asp:ListView ID="LvTemplate" runat="server" InsertItemPosition="LastItem">
                                    <EditItemTemplate>
                                        <tr style="width: 100%;">


                                            <td style="border: thin solid #C0C0C0; border-collapse: collapse;">
                                                <asp:TextBox ID="txtTemplateName1" runat="server" Text='<%#Eval("name")  %>' />
                                            </td>
                                            
                                            <td>
                                                <asp:DropDownList ID="ddlCategoryEdit" runat="server"   AppendDataBoundItems="true">
                                                </asp:DropDownList>
                                                <asp:HiddenField ID="hfTempID" runat="server" Value='<%# Eval("TempID") %>'></asp:HiddenField>
                                            </td>
                                            <td style="border: thin solid #C0C0C0; border-collapse: collapse;">
                                                <asp:TextBox ID="txtSubjectEdit" runat="server" Text='<%#Eval("subject")  %>' />
                                            </td>
                                            <td style="border: thin solid #C0C0C0; border-collapse: collapse;">
                                                <asp:ImageButton ID="btnUpdate" runat="server" ImageUrl="images/save_20.png" CommandName="Update" CommandArgument='<%# Eval("TempID")  %>' />
                                                    
                                                <asp:ImageButton ID="btnCancelEdit" runat="server" ImageUrl="images/cancel_20.png" CommandName="Cancel"  />

                                            </td>
                                        </tr>
                                    </EditItemTemplate>

Answer 1

User475983607 posted

The syntax is...

Dim item AS ListViewItem = LvTemplate.Items(e.NewEditIndex)
Dim hfTempID As HiddenField = CType(item.FindControl("hfTempID"), HiddenField)

... which can be found in the official ItemEditing handler documentation.

https://docs.microsoft.com/en-us/dotnet/api/system.web.ui.webcontrols.listview.itemediting?view=netframework-4.8

Answer 2

User646364117 posted

Hi,

Thanks for responding.

I changed my code to 

    Private Sub LvTemplate_ItemEditing(sender As Object, e As ListViewEditEventArgs) Handles LvTemplate.ItemEditing

        Dim item As ListViewItem = LvTemplate.Items(e.NewEditIndex)
        Dim hfTempID As HiddenField = CType(item.FindControl("hfTempID"), HiddenField)
        Dim TempID As Integer
        Dim catid As Integer

        TempID = Convert.ToInt16(hfTempID.Value)
        catid = GetCategoryIDForTemplate(TempID)
        'Get selected category from db and populate ddl
        Dim ddlCategoryEdit As DropDownList = CType(item.FindControl("ddlCategoryEdit"), DropDownList)
        ddlCategoryEdit.SelectedValue = catid

        LvTemplate.EditIndex = e.NewEditIndex
        BindLvTemplate()
        BindGvCategoryTemplate()
    End Sub

I moved the hidden field hfTempID unto the item template and now that is found.

However, my goal is to set the selected value of ddlCategoryEdit which is in the EditItemTemplate. 

Now this control is not being found so I don't get to the line where I set it's value

Answer 3

User475983607 posted

As I understand the original issue has been solved.  Now you have a new problem?   

Is the problem the dropdown is not bound to data?  Or maybe the selected items does not exist? 

Please take a moment to set a break point and step through your code.  Share the actual error message if there is an exception.

Answer 4

User646364117 posted

This code solved my problem. I think the key was to bind the listview in ItemEditing and then find the controls

    Private Sub LvTemplate_ItemEditing(sender As Object, e As ListViewEditEventArgs) Handles LvTemplate.ItemEditing

        LvTemplate.EditIndex = e.NewEditIndex
        BindLvTemplate()
        BindGvCategoryTemplate()
        Dim CatID As Integer

        Dim ddlCategoryEdit As DropDownList = CType(LvTemplate.EditItem.FindControl("ddlCategoryEdit"), DropDownList)
        Dim hf As HiddenField = CType(LvTemplate.EditItem.FindControl("hfCatID"), HiddenField)
        CatID = Convert.ToInt16(hf.Value)
        ddlCategoryEdit.SelectedValue = CatID


    End Sub