Controls present inside ITemplate gives error when accessed in PageLoad event RSS

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  ankur.nigam

  Member

  536 Points

  141 Posts

  Controls present inside ITemplate gives error when accessed in PageLoad event

  Sep 05, 2011 12:56 PM|LINK

  Hello,

  I am creating a templated control. Only Single instance of Template is expected in the control. If I place any control inside template and try to access its property in PageLoad event, it gives an error - "Object not set to an instance of an object." However, if I try to access the same control(which is present inside ITemplate) property in any event, it works fine returning the correct values.

  Code for control, ASPX & code-behind is as follows:

  Control Code

  Namespace MyNS
  
      <AspNetHostingPermission(SecurityAction.Demand, Level:=AspNetHostingPermissionLevel.Minimal), _
      AspNetHostingPermission(SecurityAction.InheritanceDemand, Level:=AspNetHostingPermissionLevel.Minimal), _
      ToolboxItem(False)> _
      Public Class GenericTemplateOwner
          Inherits Control
          Implements INamingContainer
  
      End Class
  
      <AspNetHostingPermission(SecurityAction.Demand, Level:=AspNetHostingPermissionLevel.Minimal), _
      AspNetHostingPermission(SecurityAction.InheritanceDemand, Level:=AspNetHostingPermissionLevel.Minimal), _
      ToolboxData("<{0}:MyControl runat=server></{0}:MyControl>"), _
      ParseChildren(True), PersistChildren(False)> _
      Public Class MyControl
          Inherits Control
          Implements INamingContainer
  
          Private _template As ITemplate
          Private _owner As GenericTemplateOwner
  
          <Browsable(False), DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)> _
          Public ReadOnly Property ContentTemplateOwner() As GenericTemplateOwner
              Get
                  EnsureChildControls()
                  Return _owner
              End Get
          End Property
  
          <Browsable(False), PersistenceMode(PersistenceMode.InnerProperty), DefaultValue(GetType(ITemplate), ""), _
          TemplateInstance(TemplateInstance.Single), Description("Control template"), _
          TemplateContainer(GetType(GenericTemplateOwner)), RefreshProperties(RefreshProperties.All)> _
          Public Overridable Property Content() As ITemplate
              Get
                  Return _template
              End Get
              Set(ByVal value As ITemplate)
                  _template = value
              End Set
          End Property
  
          Protected Overrides Sub CreateChildControls()
              Me.Controls.Clear()
              'Rendering the content of the Template
              _owner = New GenericTemplateOwner()
              If (Not Me.Content Is Nothing) Then
                  Me.Content.InstantiateIn(Me.ContentTemplateOwner)
              End If
              Me.Controls.Add(Me.ContentTemplateOwner)
          End Sub
  
          Protected Overrides Sub Render(ByVal writer As System.Web.UI.HtmlTextWriter)
              If (Not Me.Page Is Nothing) Then
                  Me.Page.VerifyRenderingInServerForm(Me)
              End If
  
              Dim tStr As New StringBuilder()
              tStr.Append("<div id=""" & Me.ClientID & """ class=""MyControl"">")
              writer.Write(tStr.ToString())
  
              MyBase.Render(writer)
  
              writer.Write("</div>")
          End Sub
  
      End Class
  
  End Namespace

  ASPX Code

      <form id="form1" runat="server">
      <div>
          <cc1:MyControl ID="MyControl1" runat="server">
          <Content>
              <asp:Button ID="Button1" runat="server" Text="Button" />
          </Content>
          </cc1:MyControl>
      </div>
      </form>

  Code-Behind Code

  Partial Class _Default
      Inherits System.Web.UI.Page
  
      Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
          'Works fine here
          Dim str As String = Button1.Text
  
      End Sub
  
      Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
          'Gives an Exception - "Object reference not set to an instance of an object."
          Dim str As String = Button1.Text
      End Sub
  
  End Class

  Kindly suggest a workaround.

  Best Regards,
  Ankur
  

  ---

  
  My Blogs:
  Twitter | DevAstrum
• • Reply
  

  Decker Dong ...

  All-Star

  118619 Points

  18779 Posts

  Re: Controls present inside ITemplate gives error when accessed in PageLoad event

  Sep 07, 2011 01:51 AM|LINK

  Hello,

  The reason is that CreateChildrenControls won't be automatically called, And you should change your codes like:

  Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
          Dim j = MyControl1.ContentTemplateOwner 'Call  EnsureChildControls()
   Response.Write(Button1.Text)
      End Sub

  • Marked as answer by ankur.nigam on Sep 09, 2011 04:54 AM
• • Reply
  

  ankur.nigam

  Member

  536 Points

  141 Posts

  Re: Controls present inside ITemplate gives error when accessed in PageLoad event

  Sep 09, 2011 04:52 AM|LINK

  Thanks Decker.

  You suggestion worked. So, in the control code, I override OnInit() and put EnsureChildControls() in it. Now control always works like a charm.

  You rock.

  Best Regards,
  Ankur
  

  ---

  
  My Blogs:
  Twitter | DevAstrum
  • Marked as answer by ankur.nigam on Sep 09, 2011 04:54 AM