WPF FAQ
Questions and answers in this FAQ have been collected from newsgroup posts, various mailing lists and the employees of Syncfusion.

3. Basic

 FAQ Home
   3.1 What is ASP.NET?
   3.2 Why does my ASP.NET file have multiple <form> tag with runat=server?
   3.3 How to find out what version of ASP.NET I am using on my machine?
   3.4 Is it possible to pass a querystring from an .asp page to aspx page?
   3.5 How to comment out ASP.NET Tags?
   3.6 What is a ViewState?
   3.7 Where can I get the details on Migration of existing projects using various technologies to ASP.NET?
   3.8 What is the equivalent of date() and time() in ASP.NET?
   3.9 How to prevent a button from validating it's form?
   3.10 How to get the IP address of the host accessing my site?
   3.11 How to access the Parameters passed in via the URL?
   3.12 How to Set Focus to Web Form Controls By Using Client-Side Script?
   3.13 How to display a Wait page while a query is running?
   3.14 How to implement Form based Authentication in ASP.NET application?
   3.15 How to catch the 404 error in my web application and provide more useful information?
   3.16 Is there a method similar to Response.Redirect that will send variables to the destination page other than using a query string or the post method?
   3.17 What are the differences between HTML versus Server Control?
   3.18 How can I change the action of a form through code?
   3.19 Is there any control that allows user to select a time from a clock - in other words is there a clock control?
   3.20 How to Compare time?
   3.21 How To work with TimeSpan Class?
   3.22 Where can I get information on Cookies in ASP.NET?
   3.23 Does ASP.Net still recognize the global.asa file?
   3.24 How should I destroy my objects in ASP.Net?
   3.25 Are there resources online with tips on ASP to ASP.Net conversions?
   3.26 How do I publish my ASP.NET application to my ISP's web server?
   3.27 Why do i get error message "Could not load type" whenever I browse to my ASP.NET web site?
   3.28 Will the WebMatrix SqlDataSourceControl work with a MySQL connection?
   3.29 Can I combine classic ASP and ASP.NET pages?
   3.30 What is the difference between src and Code-Behind?
   3.31 How can I get the value of input box with type hidden in code-behind?
   3.32 I have created a .NET user control page (.ascx) but I cannot compile and run it.
   3.33 What is a .resx file?
   3.34 Is it possible to use a style sheet class directly on a control instead of using inline or page-level formatting ?
   3.35 Can I receive both HTML markup for page and code in the ASP.NET web page's source code portion in the Web browser?
   3.36 Why can't I put <%@ Page Language="C " %> where at the top of an ASPX file and write my server-side scripts in C ?
   3.37 ASP pages that worked perfectly on Windows 2000 Server and IIS 5.0 do not work on Windows 2003 Server with IIS 6.0. ASP.NET pages work fine. Why?
   3.38 Why do I get error message "Error creating assembly manifest: Error reading key file 'key.snk' -- The system cannot find the file specified"?
   3.39 How to get URL without querystring?
   3.40 What is the best way to output only time and not Date?
   3.41 Do I have to compile code if I am changing the content of my aspx.cs file?
   3.42 How to grab the referring URL?
   3.43 My ASP code gives an error "Compiler Error Message: BC30289: Statement cannot appear within a method body. End of method assumed" when changed to .aspx?
   3.44 How can I save images ?
   3.45 How can I logout when using FormsAuthentication?
   3.46 Why do I get a blank page when I use Server.Transfer("page1.htm") to transfer to a different page?
   3.47 How to detect the User's culture?
   3.48 What is the difference between CurrentCulture property and the CurrentUICulture property?
   3.49 Can I read the hard disk serial # of the client computer using ASP.NET?
   3.50 What is xxx(src As Object, e As EventArgs)?
   3.51 What is the difference between Absolute vs Relative URLs?
   3.52 What is the difference between URL and URI?
   3.53 How to convert milliseconds into time?
   3.54 How to include multiple vb/cs files in the source?
   3.55 How to convert a string to Proper Case?
   3.56 How can I ensure that application-level variables are not updated by more than one user simultaneously?
   3.57 Why do I get the error message "System.InvalidOperationException: It is invalid to show a modal dialog or form when the application is not running in UserInteractive mode. Specify the ServiceNotification or DefaultDesktopOnly style to display a ...."?
   3.58 How to validate that a string is a valid date?
   3.59 Are namespaces and Class names Case Sensitive?
   3.60 How to convert string to a DateTime and compare it with another DateTime?
   3.61 How to get the url of page dynamically?
   3.62 How to convert user input in dMy format to Mdy?
   3.63 When the User is prompted a File Download dialogbox, if the user selects "Save" then the "Save as" dialog box is displayed. Is there any way for me to retrieve the filename and directory path specified by the user on the File Download dialog box?
   3.64 How to hide or show Controls in server side code?
   3.65 How to check if the user is using a secure or non secure connection?
   3.66 Is it possible to write code in many languages in one ASP.NET project?
   3.67 What is the difference between Response.Redirect() and Server.Transfer().
   3.68 How to get the hostname or IP address of the server?
   3.69 What is the meaning of validateRequest=true in .net framework1.1?
   3.70 What is the different between <%# %> and <%= %>?
   3.71 What permissions do ASP.NET applications posses by default?
   3.72 How can I specify the relative path for a file?
   3.73 How can I specify the "upload a file" input textbox in a form to be read only so that the user can click on the browse button and pick a file but they cannot type anything into the textbox next to the browse button.
   3.74 How to change the Page Title dynamically?
   3.75 Why do I get the error message "Object must implement IConvertible". How can I resolve it?
   3.76 Why is default.aspx page not opened if i specify http://localhost. I am able to view this page if i hardcode it as http://localhost/default.aspx?
   3.77 Can ASP.NET work on an NT server?
   3.78 Is it possible to migrate Visual InterDev Design-Time Controls to ASP.NET?
   3.79 How to automatically get the latest version of all the asp.net solution items from Source Safe when opening the solution?
   3.80 How to convert the datetime into a string for use in the SQL ' statement?
   3.81 How to make VS.Net use FlowLayout as the default layout rather than the GridLayout?
   3.82 Can I use a DataReader to update/insert/delete a record?
   3.83 What is the difference between Server.Transfer and Server.Execute?
   3.84 How to create a login screen in ASP.NET?
   3.85 How to format a Telephone number in the xxx-xxx-xxxx format?
   3.86 Can two different programming languages be mixed in a single ASPX file?
   3.87 Can I use custom .NET data types in a Web form?
   3.88 How can I have a particular Web page in an ASP.NET application which displays its own error page.
   3.89 How to use absolute positioning for controls in a web page in VS2005?
   3.90 What is an Literal Control.
   3.91 How can we programmatically verify whether the UserName and Password is Correct?
   3.92 How can users use ASP.NET to make application development easy?
   3.93 Can users create multiple interface applications?
   3.94 What are the tips for cloning ASP.NET web forms?
   3.95 How to boost web performance with multithreading?
   3.96 How can users design a custom paging solution?
   3.97 Can users use placeholder control in ASP.NET?
   3.98 Can users host ASP.NET applications?
   3.99 Could users page and sort Resultsets with ASP.NET?
   3.100 What are the tips on making ASP.NET design decisions?
   3.101 How to customize my site using WebParts?
   3.102 How to choose between Repeater, DataList and DataGrid?
   3.103 How to Manage Web Sites With ASP.NET?
   3.104 How to implement a "back" link on a web page?
   3.105 How can users Standardize their .NET Namespaces?
   3.106 How can users Visually Bind to Data in ASP.NET?
   3.107 Should users use DataReader or DataSet to retrieve data?
   3.108 How to Separate Form, Function, and Style?



3.1 What is ASP.NET?

ASP.NET is a programming framework built on the common language runtime that can be used on a server to build powerful Web applications.

For more details refer


3.2 Why does my ASP.NET file have multiple <form> tag with runat=server?

This means that ASP.Net is not properly registered with IIS.
.Net framework provides an Administration utility that manages the installation and uninstallation of multiple versions of ASP.NET on a single machine. You can find the file in C:\WINNT\Microsoft.NET\Framework\v**\aspnet_regiis.exe


use the command: aspnet_regiis.exe -u ---> to uninstall current asp.net version.
use the command: aspnet_regiis.exe -i ---> to install current asp.net version.


For Windows Server 2003, you must use aspnet_regiis -i -enable
This is because of the "Web Service Extensions" feature in IIS 6

(if you install VS.NET or the framework without IIS installed, and then go back in and install IIS afterwards, you have to re-register so that ASP.NET 'hooks' into IIS properly."


3.3 How to find out what version of ASP.NET I am using on my machine?

VB.NET


Response.Write(System.Environment.Version.ToString() )


C#


Response.Write(System.Environment.Version.ToString() );



3.4 Is it possible to pass a querystring from an .asp page to aspx page?

Yes you can pass querystring from .asp to ASP.NET page .asp


<%response.redirect "webform1.aspx?id=11"%>


.aspx
VB.NET


Response.Write (Request("id").ToString ())


C#


Response.Write (Request["id"].ToString ());



3.5 How to comment out ASP.NET Tags?


<%--<asp:Label id="Label1" style="Z-INDEX: 101; LEFT: 8px; POSITION: absolute; TOP: 48px" runat="server">Label</asp:Label>--%>



3.6 What is a ViewState?

In classic ASP, when a form is submitted the form values are cleared. In some cases the form is submitted with huge information. In such cases if the server comes back with error, one has to re-enter correct information in the form. But submitting clears up all form values. This happens as the site does not maintain any state (ViewState).

In ASP .NET, when the form is submitted the form reappears in the browser with all form values. This is because ASP .NET maintains your ViewState. ViewState is a state management technique built in ASP.NET. Its purpose is to keep the state of controls during subsequent postbacks by the same user. The ViewState indicates the status of the page when submitted to the server. The status is defined through a hidden field placed on each page with a <form runat="server"> control.


<input type="hidden" name="__VIEWSTATE" value="dDwyNTA3OTU0NDM7Oz7t5TntzkOUeB0QVV6FT2hvQwtpPw==" />


If you want to NOT maintain the ViewState, include the directive <%@ Page EnableViewState="false"%> at the top of an .aspx page If you do not want to maintain Viewstate for any control add the attribute EnableViewState="false" to any control. For more details refer The ASP.NET View State


3.7 Where can I get the details on Migration of existing projects using various technologies to ASP.NET?

Microsoft has designed Migration Assistants to help us convert existing pages and applications to ASP.NET. It does not make the conversion process completely automatic, but it will speed up project by automating some of the steps required for migration.
Below are the Code Migration Assistants

  • ASP to ASP.NET Migration Assistant
  • PHP to ASP.NET Migration Assistant
  • JSP to ASP.NET Migration Assistant
Refer Migrating to ASP.Net

3.8 What is the equivalent of date() and time() in ASP.NET?

VB.NET


System.DateTime.Now.ToShortDateString()
System.DateTime.Now.ToShortTimeString()


C#


System.DateTime.Now.ToShortDateString();
System.DateTime.Now.ToShortTimeString();



3.9 How to prevent a button from validating it's form?

Set the CauseValidation property of the button control to False

3.10 How to get the IP address of the host accessing my site?

VB.NET


Response.Write (Request.UserHostAddress.ToString ())


C#


Response.Write (Request.UserHostAddress.ToString ());



3.11 How to access the Parameters passed in via the URL?

Call the Request.QueryStringmethod passing in the key. The method will return the parameter value associated with that key. VB.NET


Request.QueryString("id")


C#


Request.QueryString["id"];



3.12 How to Set Focus to Web Form Controls By Using Client-Side Script?


<script language="javascript">
function SetFocus()
{
     // W3C approved DOM code that will work in all modern browsers     
     if (document.getElementById)
          document.getElementById('txt2').focus();
     else
     // To support older versions of IE:
     if (document.all)
          document.all("txt2").focus();
     return false;
}
</script>



<body MS_POSITIONING="GridLayout" onload="SetFocus()">
<form id="Form1" method="post" runat="server">
     Enter 1:
     <asp:TextBox ID="txt1" Runat="server" Width="50" />
     <br>
     Enter 2:
     <asp:TextBox ID="txt2" Runat="server" Width="50" />
     <br>
     <asp:Button id="Button1" runat="server" Text="Button1"></asp:Button>
</form>
</body>


Refer Sample IE Code

3.13 How to display a Wait page while a query is running?

Refer Asynchronous Wait State Pattern in ASP.NET

3.14 How to implement Form based Authentication in ASP.NET application?

For


3.15 How to catch the 404 error in my web application and provide more useful information?

In the global.asax Application_error Event write the following code

VB.NET


Dim ex As Exception = Server.GetLastError().GetBaseException()
If TypeOf ex Is System.IO.FileNotFoundException Then
     'your code
     'Response.Redirect("err404.aspx")
Else
     'your code
End If


C#


Exception ex = Server.GetLastError().GetBaseException();
if (ex.GetType() == typeof(System.IO.FileNotFoundException))
{
     //your code
     Response.Redirect ("err404.aspx");
}
else
{
     //your code
}



3.16 Is there a method similar to Response.Redirect that will send variables to the destination page other than using a query string or the post method?

Server.Transfer preserves the current page context, so that in the target page you can extract values and such. However, it can have side effects; because Server.Transfer doesnt' go through the browser, the browser doesn't update its history and if the user clicks Back, they go to the page previous to the source page.

Another way to pass values is to use something like a LinkButton. It posts back to the source page, where you can get the values you need, put them in Session, and then use Response.Redirect to transfer to the target page. (This does bounce off the browser.) In the target page you can read the Session values as required.

Refer to Passing Values Between Web Forms Pages for more information.

3.17 What are the differences between HTML versus Server Control?

Refer


3.18 How can I change the action of a form through code?

You can't change it. The action attribute is owned by ASP.NET. Handle Events and Transfer.

For work around refer to Paul Wilson's Multiple Forms and Non-PostBack Forms - Solution

3.19 Is there any control that allows user to select a time from a clock - in other words is there a clock control?

Peter Blum has developed some controls. Check out Peter's Date Package: TimeOfDayTextBox and DurationTextBox Controls

3.20 How to Compare time?

VB.NET


Dim t1 As String = DateTime.Parse("3:30 PM").ToString("t")
Dim t2 As String = DateTime.Now.ToString("t")
If DateTime.Compare(DateTime.Parse(t1), DateTime.Parse(t2)) < 0 Then
     Response.Write(t1.ToString() & " is < than " & t2.ToString())
Else
     Response.Write(t1.ToString() & " is > than " & t2.ToString())
End If


C#


string t1 = DateTime.Parse("3:30 PM").ToString("t");
string t2 = DateTime.Now.ToString("t");
if (DateTime.Compare(DateTime.Parse (t1), DateTime.Parse (t2)) < 0 )
{
     Response.Write(t1.ToString() + " is < than " + t2.ToString());
}
else
{
     Response.Write(t1.ToString() + " is > than " + t2.ToString());
}



3.21 How To work with TimeSpan Class?

VB.NET


Dim adate As DateTime = DateTime.Parse("06/24/2003")
Dim bdate As DateTime = DateTime.Parse("06/28/2003")
Dim ts As New TimeSpan(bdate.Ticks - adate.Ticks)
Response.Write(ts.TotalDays & "<br>")
Response.Write(ts.TotalHours & ":" & ts.TotalMinutes & ":" & ts.TotalSeconds & ":" & ts.TotalMilliseconds)


C#


DateTime adate = DateTime.Parse("06/24/2003");
DateTime bdate = DateTime.Parse("06/28/2003");
TimeSpan ts = new TimeSpan (bdate.Ticks - adate.Ticks);
Response.Write(ts.TotalDays.ToString () + "<br>");
Response.Write(ts.TotalHours.ToString() + ":" + ts.TotalMinutes.ToString() + ":" + ts.TotalSeconds.ToString() + ":" + ts.TotalMilliseconds.ToString() );



3.22 Where can I get information on Cookies in ASP.NET?

Refer Mike Pope's article Basics of Cookies in ASP.NET

3.23 Does ASP.Net still recognize the global.asa file?

ASP.Net does not recognize the standard ASP global.asa file. Instead it uses a file named global.asax with the same - plus additional - functionality.


3.24 How should I destroy my objects in ASP.Net?

ASP.Net actually has very solid internal garbage collection. So this is not an issue as it was in previous versions of Active Server Pages.
Link to more information: <gcConcurrent> Element


3.25 Are there resources online with tips on ASP to ASP.Net conversions?

Microsoft has designed The ASP to ASP.NET Migration Assistant help us convert ASP pages and applications to ASP.NET. It does not make the conversion process completely automatic, but it will speed up project by automating some of the steps required for migration.

The following Code Migration Assistants are discussed in the link below.

  • ASP to ASP.NET Migration Assistant
  • PHP to ASP.NET Migration Assistant
  • JSP to ASP.NET Migration Assistant
Refer Migrating to ASP.Net

Also refer:


3.26 How do I publish my ASP.NET application to my ISP's web server?

Your ISP must first create an IIS application and apply the Front Page Server Extensions to it. Then in Visual Studio .NET, select the "Project | Copy Project" menu. Then enter the URL and select the FrontPage web access method. The "Copy Project" feature copies all of the necessary files to your ISP's machine for your ASP.NET application to run.

You can also FTP your files to your ISP web server. But you must know which files to upload. For more details refer PRB: Remote ASP.NET Projects Require IIS on the Client Computer or FrontPage Server Extensions on the Server Computer

3.27 Why do i get error message "Could not load type" whenever I browse to my ASP.NET web site?

Your code-behind files for either your .aspx or the global.aspx page have not been complied. Use Visual Studio .NET's "Build | Build Solution" menu, or run the command line compiler.

For more details refer PRB: "Could not load type" error message when you browse to .aspx page


3.28 Will the WebMatrix SqlDataSourceControl work with a MySQL connection?

SqlDataSourceControl lets you connect and work with MS SQL DB, while AccessDataSourceControl do the same thing but for MS Access DB. Therefore SqlDataSourceControl can't help you in your MySql connectivity .
For Connectivity with MySql refer Accessing MySQL Database with ASP.NET


3.29 Can I combine classic ASP and ASP.NET pages?

No.
ASP pages can run in the same site as ASP.NET pages, but you can't mix in a page. Also ASP and ASP.NET won't share their session.

3.30 What is the difference between src and Code-Behind?

Src attribute means you deploy the source code files and everything is compiled JIT (just-in-time) as needed. Many people prefer this since they don't have to manually worry about compiling and messing with dlls -- it just works. Of course, the source is now on the server, for anyone with access to the server -- but not just anyone on the web.

CodeBehind attribute doesn't really "do" anything, its just a helper for VS.NET to associate the code file with the aspx file. This is necessary since VS.NET automates the pre-compiling that is harder by hand, and therefore the Src attribute is also gone. Now there is only a dll to deploy, no source, so it is certainly better protected, although its always decompilable even then.


3.31 How can I get the value of input box with type hidden in code-behind?

You can set the runat= server for the hidden control and you can use ControlName.Value to get its value in CodeBehind file

3.32 I have created a .NET user control page (.ascx) but I cannot compile and run it.

User control (ascx) can't be run on it own, but you can drag it onto any web page (aspx) and then run it.

3.33 What is a .resx file?

The .resx resource file format consists of XML entries, which specify objects and strings inside XML tags. This is useful for localization. For more details refer Resources in .resx files

3.34 Is it possible to use a style sheet class directly on a control instead of using inline or page-level formatting ?

Every WebControl derived control has a CssClass property which allows you to set it's format to a style sheet.

3.35 Can I receive both HTML markup for page and code in the ASP.NET web page's source code portion in the Web browser?

No. The Web browser receives only HTML markup.
No source code or web control syntax is passed back to the web browser.

3.36 Why can't I put <%@ Page Language="C " %> where at the top of an ASPX file and write my server-side scripts in C ?

The parsers ASP.NET uses to extract code from ASPX files understand C#, Visual Basic.NET, and JScript.NET. You can write server-side scripts in any language supported by a .NET compiler.

3.37 ASP pages that worked perfectly on Windows 2000 Server and IIS 5.0 do not work on Windows 2003 Server with IIS 6.0. ASP.NET pages work fine. Why?

Start -> Settings -> Control Panel -> Administrative Tools -> and double clicking IIS Manager.
Go to the Web Service Extensions tab, click Active Server Pages, then press the "Allow" button on the left

3.38 Why do I get error message "Error creating assembly manifest: Error reading key file 'key.snk' -- The system cannot find the file specified"?

Check the location of the key.snk file relative to the assembly file. Provide an explicit path or a relative path.


<Assembly: AssemblyKeyFileAttribute("Drive:\key.snk")>



3.39 How to get URL without querystring?

VB.NET