Selectively hiding fields in different page templates

Question

User-632673987 posted

I'm using code to hide fields in particular page templates using a custom metadata attribute based on this article

The fields specified get hidden ok, but when inserting a record I get this error:

Failed to load viewstate.  The control tree into which viewstate is being loaded must match the control tree that was used to save viewstate during the previous request.  For example, when adding controls dynamically, the controls added during a post-back must match the type and position of the controls added during the initial request

I also have some business logic in a partial class for the DataContext which sets the field's value but it doesn't get called when I get the above error. This suggests that the field is in the model (something similar to Object Data Source, I'm not sure what Dynamic Data uses) and is being checked before the business logic gets called.

Here's the code:

 HideColumnInAttribute.vb:

Imports System
Imports System.Collections.Generic
Imports System.Linq
Imports System.Web
Imports System.Web.DynamicData

''' <summary>
''' Define the HideColumnIn attribute and it's syntax
''' </summary>
''' <remarks></remarks>
<AttributeUsage(AttributeTargets.[Property])> _
Public Class HideColumnInAttribute
    Inherits Attribute
    Private _PageTemplates As PageTemplate()
    Public Property PageTemplates() As PageTemplate()
        Get
            Return _PageTemplates
        End Get
        Private Set(ByVal value As PageTemplate())
            _PageTemplates = value
        End Set
    End Property

    Public Sub New()
        PageTemplates = New PageTemplate(-1) {}
    End Sub

    Public Sub New(ByVal ParamArray lookupTable As PageTemplate())
        PageTemplates = lookupTable
    End Sub

    Public Shared [Default] As New HideColumnInAttribute()
End Class

''' <summary>
''' Define page templates in /DynamicData/PageTemplates
''' </summary>
''' <remarks></remarks>
Public Enum PageTemplate
    Details
    Edit
    Insert
    List
    ListDetails
    ' add any custom page templates here
End Enum

  

HideColumnFieldsManager.vb:

Imports System
Imports System.Collections
Imports System.Collections.Generic
Imports System.Linq
Imports System.Web.DynamicData
Imports System.Web.UI

Public Class HideColumnFieldsManager
    Implements IAutoFieldGenerator
    Protected _table As MetaTable
    Protected _currentPage As PageTemplate

    Public Sub New(ByVal table As MetaTable, ByVal currentPage As PageTemplate)
        _table = table
        _currentPage = currentPage
    End Sub

    Public Function GenerateFields(ByVal control As Control) As ICollection Implements IAutoFieldGenerator.GenerateFields
        Dim oFields = New List(Of DynamicField)()
        Dim Hidden As Boolean ' whether column should be hidden or not
        For Each column In _table.Columns

            ' show column if scaffolded, not a long string in a list page and not hidden
            If column.Scaffold = True Then
                Hidden = False
                If ((column.IsLongString = True) And (_currentPage = PageTemplate.List)) Then
                    Hidden = True
                End If
                If column.IsHidden(_currentPage) = True Then
                    Hidden = True
                End If
            Else
                Hidden = True
            End If

            If Hidden = False Then
                Dim f = New DynamicField()

                f.DataField = column.Name
                oFields.Add(f)
            End If

        Next
        Return oFields
    End Function
End Class

Public Module ExtensionMethods
    Sub New()
    End Sub
    <System.Runtime.CompilerServices.Extension()> _
    Public Function IsHidden(ByVal column As MetaColumn, ByVal currentPage As PageTemplate) As Boolean
        Dim hideIn = TryCast(column.Attributes.OfType(Of HideColumnInAttribute)().DefaultIfEmpty(New HideColumnInAttribute()).First(), HideColumnInAttribute)
        Return hideIn.PageTemplates.Contains(currentPage)
    End Function
End Module

 

./DynamicData/PageTemplates/Edit.aspx.vb has this line added:

' reference HideColumnFieldsManager so we can customise fields to display based on a metadata attribute
        DetailsView1.RowsGenerator = New HideColumnFieldsManager(table, PageTemplate.Edit)

 

and the metadata for the field is set like so:

  

<HideColumnIn(PageTemplate.Edit)> _
        Public Property tktDateEntered() As Object
            Get
            End Get
            Set(ByVal value As Object)
            End Set
        End Property

 

 

Answer 1

User-1005219520 posted

What happens when you disable viewstate? You might not need it.

Answer 2

User-797310475 posted

./DynamicData/PageTemplates/Edit.aspx.vb has this line added:

' reference HideColumnFieldsManager so we can customise fields to display based on a metadata attribute
        DetailsView1.RowsGenerator = New HideColumnFieldsManager(table, PageTemplate.Edit)

The solution to your problem is to move the quoted code to Page_Init. Page_Load is too late.