Custom Server Controls :: Page Cannot Be Null Error, Or Blank Databound Controls
Feb 24, 2011
So I finally managed to create a control which basically shows a bunch of Panels with an extra property. I use it like this:
[Code]....
This renders fine and shows the text in the TabPanel controls. However, when I replace the plain text with something a little more exciting, say an UpdatePanel so it looks like this:
[Code]....
Then I get this weird error:
Page cannot be null. ensure that this operation is being performed in the context of an ASP.NET request.[InvalidOperationException: Page cannot be null. ensure that this operation is being performed in the context of an ASP.NET request.] System.Web.UI.UpdatePanel.get_IPage() +647672 System.Web.UI.UpdatePanel.Render(HtmlTextWriter writer) +20 SP.adminonly_reports_loginreport_aspx.__RenderTabPanel1(HtmlTextWriter __w, Control parameterContainer) in D:....eport.aspx:37 System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +115 System.Web.UI.WebControls.WebControl.RenderContents(HtmlTextWriter writer) +13 System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer) +42 TabPanels.TabPanelHolder.Render(HtmlTextWriter w) in D:e4Webwwwrootlms_workingTabPanelsTabPanelsTabPanelHolder.vb:146 System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +240 System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +240 System.Web.UI.HtmlControls.HtmlForm.RenderChildren(HtmlTextWriter writer) +253 System.Web.UI.HtmlControls.HtmlForm.Render(HtmlTextWriter output) +87 System.Web.UI.HtmlControls.HtmlForm.RenderControl(HtmlTextWriter writer) +53 System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +240 System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +240 System.Web.UI.Page.Render(HtmlTextWriter writer) +38 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +4240
If I take out the UpdatePanel and replace it with an ASCX control I made that simply puts database data into some DropDownLists, like this...
[Code]....
Then the page loads, but the data is not loaded into CustomerUserList1, and the dropdownlists within it are all blank. CustomerUserList1 has worked fine for years when used directly in a normal Panel/Page UpdatePanel.
I have a control that renders different children according to a property value. All works great until I add a rating control in the mix. I get the following:
Page cannot be null. ensure that this operation is being performed in the context of an ASP.NET request.
I have a DetailsView control bound to an ObjectDataSource within a User Control (.ascx). It appears that the DetailsView.OnDataBound event is being fired on every page load or postback.
I do not see this behavior with a similiar DetailsView directly placed on an aspx page.
The following code works well as long as I pass a querystring value to the datalist.
Private Sub BindGrid() Dim id As Integer = Integer.Parse(Context.Request.QueryString("id")) Dim strConnString As String = ConfigurationManager.ConnectionStrings("Conn").ConnectionString Using con As New SqlConnection(strConnString) Using cmd As New SqlCommand() cmd.CommandText = "select Id, Name from tblFiles where Id=@Id"
[Code] ......
However, the page errors with the message "Value cannot be null." if I don't pass a value. I know that DataList does not have an EmptyItem Property like a Gridview control. I do not want the page to error if I don't pass a value. Need info to deal with empty values in a datalist.
Most websites have pointed me to this code to use:
The 'list' throws an error. The error is "Too few type arguments to 'System.COllections.Generic.List". I am not sure if the code is written in C# and that is what is causing the error. It seems that it should work but I can not figure out the 'list' error.
I want to make a link in databound data which is stockQtt. How can I do that? and I want target is blank and the link page is AdjStock.aspx below is coding.
I have a table in sql having a numeric data type column,Now i want that whenever user left this field blank from front end aspx page, null value should be inserted in this column from stored proc.How can i achieve this? Also what kind of data type is most appropriate on front end for such taking kind of value?
I have implemented a custom ErrorController with UnknownError Action returning the View "~/Error/UnknownError" (not inside the Shared folder).
I have also modified the web.config file and add in custom errors section the following[Code]....
Inside the UknonwnError page i would like to display some information concerning the error occured using the HandleErrorInfo.
To test the error handling mechanism, i throw a custom ApplicationEcxeption from my Home/About controller action that is handled via the HandleErrorAttribute on the controller level.
The result is to get another unhandled exception thrown from the UknownError page due to the fact that HandleErrorInfo model is null.
Although I'm a huge fan of Databound controls since ASP.Net 2.0 and have been using them a lot since learning them, I seem to have stumbled upon an unnoticed(or rather not cared about) issue that these controls seem to have.
I'm using ASP.Net 3.5 and the issue that I noticed is that when using Databound controls(such as Labels, HyperLinks) inside a Data-Control(such as Datalist, Gridview etc.), even if the value returned for one column is NULL, it is still rendered albeit as an empty tag.
For eg: I have a Datalist in which I have a Label whose value may or may not be NULL. Now there's no problem when the value is not NULL, the problem is when the value is NULL. Ideally, no HTML should be rendered for a controls that don't have any value, but in this case, the HTML(<span></span> in case of the Label) of the corresponding NULL valued control is still being rendered.
Now, as I said earlier that most people won't care about this as it isn't much of an issue, but if you consider the fact that this control may be enclosed in a hierarchy of parent controls, and then repeated many a times, this could significantly increase the HTML content(since the ID of your HTML content is based on the parent controls) without any Text added to maintain the Text/HTML ratio, thereby becoming a cause for the Search Engines to shy away from indexing your pages fully.
I couldn't find anything related to this matter anywhere else so I thought to bring it up here. Is this really an issue with databound controls or am I missing something here?
I have created a custom control from scratch and it works fine as in you can build the project that uses it and it works fine at runtime. Problem is when you go to design view the control shows an error in the place of where the control should be rendered.
Error: '<SomeValue>' Could not be set to '<SomeProperty>'
This shows up on all my custom set properties. These properties are created as basic as possible. I can give the properties values in Source view and run the app just fine. I can even add a Onclick event. If I don't set any custom properties the control will render fine in Design view. It's only when I set a value to a custom property.
Property Code Example:
[Code]....
I've even removed the Category and Description tags with no difference.
I don't know if what I said makes sens, but I hope it does.
I was referred here by MSDN forums hope this is the right place - I have a custom control (:WebControl) that renders web.sitemap in a specific way. While it runs error free and produces the expected result, at Design-Time it complains
[Code]....
and have tried the SiteMapDataProvider Tag with and without the SiteMapProvider attribute.Does anybody have (a) any experience with this, or (b) any suggestions as to how to track down the problem?
I have to use inline code for an aspx page and I need to use a custom server control that is defined in the same aspx page but the control does not get processed as a server control. it gets returned as is as static html tag.
Is there a way to convert nulls in all the fields in a table into blanks using transact sql? For example strings will be "", numbers will be 0, and dates will be "1/1/1901".
I have over 500 columns, I don't want to go over each column and change the default value.
Every thing is fine but when I execute the project, NO control on my user control gets "instantiated" and thus I receive error "Object Reference Not Set"
Note that My Control has,
1) Public property PublicProperty as String
2) 1 Label control
In Load Event Handler I am setting Text property of Label Control to PublicProperty. Here object reference NOT set error occurs (which means Label control is NOT initialized).I don't want to register my control using Src, TagPrefix etc.
I have a FormView that is loaded with a records from my DB. Some of the fields may be blank or null. I am trying to check the value of some of the text boxes to verify that the user has updated the fields prior to allowing a DB update from the Edit Template.
I can not seem to get the correct syntax on the if statment to check the value of the text box....
I'm working on a website to showcase some of my bird photography, using ASP.NET 2.0 and C# with a SQLServerExpress backend.What I have right now is a ListBox bound to my database that displays a list of common names of birds and when the user clicks on an item in the listbox the main image on the page is changed to the image for that bird. For style reasons I want the listbox to always be a fixed size and because I specify the size (using CSS) a vertical scrollbar appears. My problem is that I want to provide my own images of arrows that go above and below the box such that when the user hovers over an arrow the box scrolls slowly and when the user clicks an arow the box scrolls quickly. Finally, my main problem is that I want to get rid of the ugly default vertical scrollbar that comes with ListBox.
Can you guys help me figure out how to do this? I don't mind using a different control other than ListBox as long as it is available in ASP.NET 2.0 and as long as it can be bound to my db. I also don't mind using JavaScript (which I'm sure I'll end up doing for the hover effects). Right now I'm fooling around with subclassing the ListBox control but I've never subclassed a control before so I'm somewhat clueless.
I am trying to develop a very simple templated custom server control that resembles GridView. Basically, I want the control to be added in the .aspx page like this:
[Code]....
I know that what I want to achieve is pointless and that I can use DataGrid to achieve it, but I am giving this very simple example because if I know how to do this I would be able to develop the control that I need.
When I add an update command to my page and run the page I get this error message
Server Error in '/MYApplication.
Incorrect syntax near '-'.Must declare the scalar variable "@recnum".
Description:An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.Data.SqlClient.SqlException: Incorrect syntax near '-'.Must declare the scalar variable "@recnum".
Source Error:
[Code]....
Stack Trace: [Code]....
Version Information: Microsoft .NET Framework Version:2.0.50727.3082; ASP.NET Version:2.0.50727.3082
I have a 2 page signup form, on each page the form fields are seperated into sections. Each section is a user control, and there are 2 controls on each page. My question is, how do I get the data from page A to B. I'll be using a webservice to insert the data into SQL so I'm not worried about that portion of the process.
using System; using System.Collections.Generic; using System.Configuration; [code]....
I am trying to build a custom composite control, which allows me to add custom content to each child control. It's a similar concept to what you have with a GridView and TemplateColumn. The markup used to place the control on the page would end up being something like this:
[Code]....
I have the code below, which allows me to put that markup on the page without throwing any errors, and it renders all the correct HTML, except it doesn't render the contents of the ColumnTemplate. I have replaced the Render() code with a comment because it's quite long winded and doesn't add anything important here:
[Code]....
I have tried to follow examples on MSDN and other forums but I can't make this work. I think I'm missing the code to render the contents of the template, but I don't know how to hook that up.
I'm building a dynamic form using XML and XSLT. Anyway I'm using a custom asp.net control for CKEditor, it's an HTML editor.
When I try to add the controls from the XSLT using Page.ParseControl(<the-string-from-the-xslt-here>), I get a warning saying:
Unknown server tag 'FCKeditor.CKEditor'
And of course, if I remove the control from the XSLT everything is working fine and all the regular asp.net controls like TextBox etc get rendered to the string just fine. Does anyone know what I can do about it?
I'm trying to create a web server control with a css embedded in the assembly.
I marked it as an embedded resource, add assembly attribute to reference it and use the proper methods to include the link to that
css in html code... my page renders ok witk something like <link href='/WebResources.axd?....' />
That's when the problem appears! My control isn't using the css as it appears to not found webResources.axd
I tried directly in web browser to locate http://locahost/mysite/WebResources.axd and it came with http code 404 NOT FOUND
In my IIS i have uncheked "Verify if file exists" on my extensions mapping related to .axd I add HEAD verb in Web.Config to path WebResources.axd and the result is always the same
I have some (probably very basic) questions about developing custom controls. I am wanting to derive a set of button controls, and the first one I have started on is a "DeleteButton", that has a additional property (DeleteConfirmationText) that is built into the OnClientClick attribute. To get that added, I overrode the Render method as follows:
[Code]....
This all works well. Now, I will add some logic to make sure that there is some text in the DeleteConfirmationText property, but that isn't the intent of my question. What I am also wanting to do is to override some of the default property values, so I added that to the default constructor:
[Code]....
Now, in the designer in VS2008, and I look at the properties for the control, there isn't a default value shown in the "Properties" section, and the Causesvalidation still shows the underlying classes default value of "True". As well, in design mode, where the GridView control that containse my DeleteButton control would be displayed, there is an error box "There was an error rendering the control. 'Are you certain you want to delete this attorney?' cound not be set on property 'DeleteConfirmationText'. Here's the markup where I am defining the deletebutton control:
