Dot Net World

Populating the Menu using the Database

2012-01-17T09:59:00.000-08:00

Suppose you have developed web application with multiple pages and want to give access of pages through web application then you will like to store selected pages and options into database  which you want to populate the Menu. The code below shows how you can use database as a data source:

Private Sub populateMenu()

Dim ds As DataSet
ds = GetDataSetForMenu()
Dim mmenu As New Menu
mmenu.Font.Name = "Arial"
mmenu.Font.Size = 11
mmenu.Height = 25
mmenu.Orientation = Orientation.Horizontal
mmenu.BackColor = Drawing.Color.DarkBlue
mmenu.ForeColor = Drawing.Color.LightBlue
mmenu.DynamicVerticalOffset = 8
mmenu.DynamicMenuStyle.BackColor = Drawing.Color.DarkBlue
mmenu.DynamicMenuStyle.ForeColor = Drawing.Color.White
mmenu.DynamicMenuStyle.HorizontalPadding = 5
mmenu.DynamicHoverStyle.BackColor = Drawing.Color.Blue
mmenu.DynamicHoverStyle.ForeColor = Drawing.Color.LightSteelBlue
mmenu.DynamicHoverStyle.Height = 20
mmenu.DynamicMenuItemStyle.ItemSpacing = 5

For Each parentItem As DataRow In ds.Tables("mdesc").Rows

   Dim categoryItem As New MenuItem(DirectCast(parentItem("modulecat"), String))
   mmenu.Items.Add(categoryItem)

   For Each childItem As DataRow In parentItem.GetChildRows("Children")

      Dim childrenItem As New MenuItem(DirectCast(childItem("moduledesc"), String))
      Dim childrenNavigateItem As New MenuItem(DirectCast(childItem("modulefilename"), String))
      categoryItem.ChildItems.Add(childrenItem)
      childrenItem.NavigateUrl = childItem("modulefilename").ToString

   Next

Next

Dim cItem As New MenuItem(DirectCast("Logout", String))

mmenu.Items.Add(cItem)

cItem.NavigateUrl = "logout.aspx"

Panel1.Controls.Add(mmenu)

Panel1.DataBind()

End Sub

Private Function GetDataSetForMenu() As DataSet

Dim myConnection As New SqlConnection(SqlDataSource1.ConnectionString)
Dim adCat As New SqlDataAdapter("SELECT distinct modulecat, modulecatseq FROM UserProfileQueryNew where muserid='" & useridlbl.Text & "' order by modulecatseq", myConnection)
Dim adProd As New SqlDataAdapter("SELECT * FROM userprofilequerynew where muserid='" & useridlbl.Text & "'", myConnection)
Dim ds As New DataSet()
adCat.Fill(ds, "mdesc")
adProd.Fill(ds, "mchild")
ds.Relations.Add("Children", ds.Tables("mdesc").Columns("modulecat"), ds.Tables("mchild").Columns("modulecat"))

Return ds

End Function

Sys.WebForms.PageRequestManagerParserErrorException - what it is and how to avoid it

2011-09-26T10:35:00.000-07:00

If you've used the Microsoft ASP.NET AJAX UpdatePanel control, there's a good chance you've hit the "Sys.WebForms.PageRequestManagerParserErrorException" error.

What's a PageRequestManagerParserErrorException?

The UpdatePanel control uses asynchronous postbacks to control which parts of the page get rendered. It does this using a whole bunch of JavaScript on the client and a whole bunch of C# on the server. Asynchronous postbacks are exactly the same as regular postbacks except for one important thing: the rendering. Asynchronous postbacks go through the same life cycles events as regular pages (this is a question I get asked often). Only at the render phase do things get different. We capture the rendering of only the UpdatePanels that we care about and send it down to the client using a special format. In addition, we send out some other pieces of information, such as the page title, hidden form values, the form action URL, and lists of scripts.

As I mentioned, this is rendered out using a special format that the JavaScript on the client can understand. If you mess with the format by rendering things outside of the render phase of the page, the format will be messed up. Perhaps the most common way to do this is to call Response.Write() during Page's Load event, which is something that page developers often do for debugging purposes.

The client ends up receiving a blob of data that it can't parse, so it gives up and shows you a PageRequestManagerParserErrorException. Here's an example of what the message contains:

---------------------------

Microsoft Internet Explorer
---------------------------
Sys.WebForms.PageRequestManagerParserErrorException: The message received from the server could not be parsed. Common causes for this error are when the response is modified by calls to Response.Write(), response filters, HttpModules, or server trace is enabled.

Details: Error parsing near 'Hello, World!106upd'.
---------------------------
OK
---------------------------

If you ask me, this error message is not all that bad. After all, I'm the one that made it :) The details indicate what was being parsed when it decided to give up. You can see the part of the text from my Response.Write(), and immediately after that is part of the special format I keep mentioning.

Why do I keeping getting a PageRequestManagerParserErrorException?

Well, chances are you're doing one of the things mentioned in the error message. Here are the most common reasons and why they don't work:

1- Calls to Response.Write():
By calling Response.Write() directly you are bypassing the normal rendering mechanism of ASP.NET controls. The bits you write are going straight out to the client without further processing (well, mostly...). This means that UpdatePanel can't encode the data in its special format.

2- Response filters:
Similar to Response.Write(), response filters can change the rendering in such a way that the UpdatePanel won't know.

3- HttpModules:
Again, the same deal as Response.Write() and response filters.

4- Server trace is enabled:
If I were going to implement trace again, I'd do it differently. Trace is effectively written out using Response.Write(), and as such messes up the special format that we use for UpdatePanel.

5- Calls to Server.Transfer():
Unfortunately, there's no way to detect that Server.Transfer() was called. This means that UpdatePanel can't do anything intelligent when someone calls Server.Transfer(). The response sent back to the client is the HTML markup from the page to which you transferred. Since its HTML and not the special format, it can't be parsed, and you get the error.

How do I avoid getting a PageRequestManagerParserErrorException?

To start with, don't do anything from the preceding list! Here's a matching list of how to avoid a given error (when possible):

1- Calls to Response.Write():
Place an or similar control on your page and set its Text property. The added benefit is that your pages will be valid HTML. When using Response.Write() you typically end up with pages that contain invalid markup.

2- Response filters:
The fix might just be to not use the filter. They're not used very often anyway. If possible, filter things at the control level and not at the response level.

3- HttpModules:
Same as response filters.

4- Server trace is enabled:
Use some other form of tracing, such as writing to a log file, the Windows event log, or a custom mechanism.

5- Calls to Server.Transfer():
I'm not really sure why people use Server.Transfer() at all. Perhaps it's a legacy thing from Classic ASP. I'd suggest using Response.Redirect() with query string parameters or cross-page posting.

Another way to avoid the parse error is to do a regular postback instead of an asynchronous postback. For example, if you have a button that absolutely must do a Server.Transfer(), make it do regular postbacks. There are a number of ways of doing this:

1- The easiest is to simply place the button outside of any UpdatePanels. Unfortunately the layout of your page might not allow for this.

2- Add a PostBackTrigger to your UpdatePanel that points at the button. This works great if the button is declared statically through markup on the page.

3- Call ScriptManager.RegisterPostBackControl() and pass in the button in question. This is the best solution for controls that are added dynamically, such as those inside a repeating template.

Summary

I hope I've answered a lot of questions here and not angered too many of you. We're looking at ways to improve some of these situations in the next version of ASP.NET, but of course there are no guarantees. If you avoid changing the response stream, you're good to go. If you absolutely must change the response stream, simply don't do asynchronous postbacks.

How to remove error "'Sys' is undefined" ASP.NET

2009-07-07T00:26:00.000-07:00

When anyone create a normal "ASP.NET Web Site" and not an "ASP.NET Ajax Enabled Web Site" and try to use AJAX Controls this error occurs.

There are two key tags, that must exist on web.config:

under <assemblies> (possibly you already have this one)
<add assembly="Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>

under <httpHandlers> (this is the new one)
<add verb="GET" path="ScriptResource.axd" Type="Microsoft.Web.Handlers.ScriptResourceHandler" validate="false"/>

If you use AJAX controls always try to create AJAX Enabled website.

If you already created Normal website and wish to use AJAX Controls you can copy following tag alongwith codes from WebConfig file from any AJAX Enabled website.

Copy assembly under assemblies tag;
copy httpHandlers tag and code under it; and
copy code under httpModules alongwith httpModules tag.

Where does cookies are stored in local Hard drive ?

2009-05-05T11:40:00.000-07:00

This is one of the interesting things to find out the cookies in your local drive. First of all, From "Explorer Folder Option ", Select, show hidden files and folder.

Fig 1.2 : Show Hidden files and Folder Settings

Now Browse into document & settings of the current user and open the cookies folder. Now looks the picture.

Fig 1.3 : Reading Cooking info in local System

How to Read data from cookies ?

2009-05-01T08:34:00.000-07:00

Now , its times to retrieve data from cookies. Ok, before reading cookies, first of all we need to check whether a cookies was found or not. "Its always good practice to check cookie before read it, because is browser is disable cookies.

How to create cookies ?

2009-05-01T08:27:00.000-07:00

For working with cookies we need to use namespace System.web

Now , have a look, on the code , that how can we create a cookies and add it with web response .3

The cookies which has been created will persist , until browser has been closed. we can persist the cookies. But how? Just after few point I have discussed it.

Advantages & Disadvantages of of Cookies

2009-05-01T08:23:00.000-07:00

Advantages

Following are main advantages of using cookies in web application:

It's very simple to use and implement.
Browser's taking care send data.
For multiple sites cookies, Browser automatically arranges them.

Disadvantages

Main disadvantages of cookies are:

Its store data in a simple text format. so it's not secure at all.
There is a size limit of cookies data ( 4096 bytes / 4KB).
Number if cookies also limited. Most Browser provides limits of storing cookies is 20. If new cookies came, it will discard the old one. Some of browser support up to 300.
We need to configure browser. It will not work on a high security configuration of browser. [I have explained about this in details.]

How Cookies are started ?

2009-05-01T08:15:00.000-07:00

When client request to the server, server send the cookies into client . The same cookies can be referred for subsequent request. As for example, if codeproject.com stores session id as a cookies, when any client hits first times on the server, server generates the session id and send it as a cookies to client. [As given in Fig 1.0]

Fig 1.0 : Initial state of cookie creation

Now for all other subsequent from the same client it uses the session-id from cookies, just like the picture below:

Fig 1.1 : Subsequent request for other pages

Browser and web server are responsible for exchange cookies information. For different sites, browser keeps cookies differently. If any pages need information from cookies, when that URL is being hit, first its search for local system for cookies information then its moved to server with that information.

What are Cookies ?

2009-05-01T08:09:00.000-07:00

Cookies are the small files that are created on the client's system or client browser memory (if temporary). Its use for State management that I have already discuss on my view state article. So we can store small piece of information in a client system and we can use it when we needed. Most interesting thing is that Its works transparently with the user. It can be easily used any where of you web application. Cookies store information in a plain text format. If any web application using cookies, Server send cookies and client browser will store it. The browser then returns the cookie to the server at the next time the page is requested. The most common example of using a cookie is to store User information, User preferences , Password Remember Option etc. Cookies has many advantages and disadvantages. I will comes to this points , but first have a look how cookies are started.

FileUpload control in ASP.NET web form using c#

2009-04-30T03:11:00.000-07:00

FileUpload is very simple control allows user to select file and upload.

You can easily handle that with very little coding and ease. I have given the full code behind for this functionality.

First create a aspx page with 3 controls

FileUpload: rename it to FileUpload1

Label: rename it to lblMsg

Button: rename it to btnAdd

Copy this code in your code behind file inside the class declaration. As you can see we are simply calling theSaveUploadedFile() function to save the uploaded file. you can check for the particular extension within the function right now we are checking for only 3 extensions. You can change it in sAllowedExt string.

Here is the code behind stuff:

String UPLOAD_PATH = "";
int MAXSIZE = 5 * 1024 * 1024; // max 5 MB
String sAllowedExt = ",.doc,.pdf,.xls,";  // make sure whatever extension you enter, string ends with comma
protected void Page_Load(object sender, EventArgs e)
{
    btnUpload.Attributes.Add("onclick", "return checkFile();");
    UPLOAD_PATH = Server.MapPath("~/UploadedDocs") + "/";
}
private void setMsg(String sMsg)
{
    lblMsg.Text = sMsg;
}
protected void btnAdd_Click(object sender, EventArgs e)
{
    try
    {
        SaveUploadedFile();           
    }
    catch (Exception ex)
    {
        //Response.Write("Error: " + ex.Message);
        setMsg("File could not be uploaded successfully.");       
    }
}

private void SaveUploadedFile()
{
    if (FileUpload1.HasFile)
    {
        String fileExtension =  System.IO.Path.GetExtension(FileUpload1.FileName).ToLower();
        String validExt = ;
        if (validExt.IndexOf("," + fileExtension + ",") != -1)
        {               
            if (FileUpload1.FileBytes.Length <= MAXSIZE)
            {
                FileUpload1.PostedFile.SaveAs(UPLOAD_PATH + FileUpload1.FileName);
                setMsg("File uploaded successfully.");
            }
            else
            {
                setMsg("File size exceeded the permitted limit.");
            }
        }
        else
        {
            setMsg("This file type is not accepted.");
        }
    }       
}
Once the user uploads the file, it's availabe using FileUpload.PostedFile.SaveAs() method. You can then directly save that file to particular folder with new name. We are checking FileUpload1.HasFileto make sure we only process if a file is uploaded.

ASP.NET event firing twice

2009-04-29T22:05:00.000-07:00

First Solution:

This seems to be a very common problem where by your event handler method gets run twice.
It is caused by VS.NET inserting 2 wireup of the event handler:

once in the aspx (HTML) eg:
and once in the VS.NET generated section (InitializeComponent) eg:

this.btnTest.Click += new System.EventHandler(this.btnTest_Click);

The easiest solution, imo, is to simply remove the "OnClick..." HTML markup from the .aspx page.
e.g: change this: < asp:Button ID="btnTest" runat="server" Text="Test" OnClick="btnTest_Click" >

To this: < asp:Button ID="btnTest" runat="server" Text="Test" >

Rebuild, and bingo! - 1 event per click.

Second Solution:

I had the same problem, but none of the solutions above solved my problem..I was using HTML controls on my aspx page like < button runat="server" id="btnNext" type="submit" onserverclick="btnNext_Click" > The solution for me was to change the type="submit" to type="button".

Large file uploads in ASP.NET

2009-04-29T20:57:00.000-07:00

Uploading files via the FileUpload control gets tricky with big files. The default maximum filesize is 4MB - this is done to prevent denial of service attacks in which an attacker submitted one or more huge files which overwhelmed server resources. If a user uploads a file larger than 4MB, they'll get an error message: "Maximum request length exceeded."

Increasing the Maximum Upload Size

The 4MB default is set in machine.config, but you can override it in you web.config. For instance, to expand the upload limit to 20MB, you'd do this:

<system.web>

</system.web>

Since the maximum request size limit is there to protect your site, it's best to expand the file-size limit for specific directories rather than your entire application. That's possible since the web.config allows for cascading overrides. You can add a web.config file to your folder which just contains the above, or you can use the tag in your main web.config to achieve the same effect:

<system.web>

</system.web>

</location>