Unable to save values into SQL Server from dynamically generated ASP.NET Controls

Question

I have an asp.net web forms application. In this application, students upload assignments and submit a survey along with it. For the survey, I read values from DB and dynamically generate ASP.NET Controls like radiobuttonlist, checkboxlist, textbox on the form during gridview's RowDataBound Event. I cannot do it in Page_Init method because I create only if a user click on a specific assignment which requires a survey to be submitted.

When I submit the survey form, the survey values are not saved into database. During debugging I figured it out that the values are not available in the codebehind page. The radiobuttonlist.selectedvalue returns “” and I get following error:

String conversion from “” to integer not valid.

After a postback, the form values are still there and I don’t know why they are not accessible in the codebehind. And I am confused because viewstate is enabled on all controls.

Dim lstContextArtifacts As New List(Of ContextAttributesArtifacts) 

                            Dim lstContextAttributesOpen As New List(Of ContextAttributesArtifactsOpenEnded)     
    For Each gvrow As GridViewRow In gridview_ContextAttributes.Rows
     If gvrow.RowType = DataControlRowType.DataRow Then

       Dim contextAttribute As New ContextAttributesArtifacts
       Dim contextAttributeOpen As New ContextAttributesArtifactsOpenEnded

    Select Case gvrow.Cells(1).Controls(1).ID.ToString()
    Case "rdblist"
        Dim _radiobtnlist As RadioButtonList = DirectCast(gvrow.Cells(1).FindControl("rdblist"), RadioButtonList)
        contextAttribute.ContextAttributeOptionID = _radiobtnlist.SelectedValue
        contextAttribute.ContextAttributeID = CType(gridview_ContextAttributes.DataKeys(gvrow.DataItemIndex).Value, Integer)
        contextAttribute.ArtifactID = varArtifactID
        lstContextArtifacts.Add(contextAttribute)
      End Select
    End If
    Next

I receive error on the following line:

contextAttribute.ContextAttributeOptionID = _radiobtnlist.SelectedValue

I am able to cast radiobuttonlist from gridview but values are inaccessible even though they still persist after postback.

Thanks in advance for the help.

UPDATE1: I referred to these articles which kind of relate to my problems http://www.4guysfromrolla.com/articles/092904-1.aspx

http://msdn.microsoft.com/en-us/library/Aa479007

http://www.codeproject.com/KB/aspnet/dynamiccontrolsByLeon.aspx as suggested by @coding gorilla in the answer below.

However, I generate those controls when a user click on the assignment, then it checks whether it requires a survey or not. If it does then I generate controls in grid view rowdatabound event which allows me to check which controls I need to load. I do not load them in page load event which above articles refer. Or as articles mention how do I load them on each page request because it depends on user behavior. Sorry but please correct me if I misunderstood anything.

I think the values a user selects are not getting saved in the viewstate.

UPDATE2: I am giving the code that generates on gridviewdatabound event. And I am even databinding my gridview on postback to regenerate the dynamic controls. And they seems to preserve control selection but are inaccessible in codebehind.

If e.Row.DataItemIndex > -1 Then
            Dim label1 As Label = DirectCast(e.Row.Cells(0).FindControl("lbl_ca"), Label)
            '  'MsgBox(label1.Text)
            Dim FormElement As Label = DirectCast(e.Row.Cells(0).FindControl("lbl_FormElement"), Label)

            Select Case FormElement.Text

                Case "radio"
                    ''Add Custom Logic Here
                    Dim rdblist As New RadioButtonList
                    rdblist.ID = "rdblist"
                    rdblist.EnableViewState = True
                    rdblist = myRadioButtonList(gridview_ca.DataKeys(e.Row.DataItemIndex).Value)
                    Dim v1 As New RequiredFieldValidator
                    v1.ControlToValidate = "rdblist"
                    v1.ValidationGroup = "valSurvey"
                    v1.Text = "*"
                    v1.ForeColor = Drawing.Color.Red
                    v1.SetFocusOnError = True
                    v1.Display = ValidatorDisplay.Dynamic
                    Dim t1 As String = Now.ToLongTimeString.ToString.Replace(":", "")
                    t1 = t1.Replace("/", "")
                    t1 = t1.Remove(t1.Length - 3, 3)
                    t1 = t1.Replace(" ", "")
                    v1.ID = "val" + t1
                    e.Row.Cells(1).Controls.Add(v1)
                    e.Row.Cells(1).Controls.Add(rdblist)

            End Select
        End If

UPDATE 3: I ended up using an alternative way to grab values from the controls. The controls values persist when I try to check their values on onserver validate event. So Inserted a subroutine to grab values and store them temporarily and retrieve them later.

Although I feel this article series was very useful in understanding dynamically added controls.

http://weblogs.asp.net/infinitiesloop/archive/2006/08/30/TRULY-Understanding-Dynamic-Controls-_2800_Part-3_2900_.aspx

CodingGorilla CodingGorilla · Accepted Answer · 2011-07-13T14:34:03

This can be a very complex issue, but the basics of the issue are this:

What you dynamically generate asp.net controls, after a postback, you have to re-generate those controls before attempting to use those controls. The problem is that your code-behind only contains controls that are directly created by parsing the .aspx file.

Keep in mind that every time a page request is generated, including a post-back, the class that is represented by your .aspx.cs file is re-created (i.e. newed up). So if on the initial rendering you create your checkboxlist control, and store it in an instance field. After the page is rendered, that particular class is destroyed and when the post-back comes in it's recreated.

So for the postback, you have to recreate those controls exactly the same way as when you originally created them, and this has to happen before the post back data is loaded. If not, then the data is available as a form field in the HTTP request, but ASP.NET doesn't know what to do with it.

There are a lot of postings on how to do this kind of thing if you just search "dynamically created asp.net controls". A quick search brought me to this one: http://www.codeproject.com/KB/aspnet/dynamiccontrolsByLeon.aspx

Unable to save values into SQL Server from dynamically generated ASP.NET Controls

1 Answers