< Coding Resource >

.NET Custom DateTime Format Strings

2010-09-05T20:56:00.000-07:00

To have a more flexible DateTime format the DateTime object's ToString function can be used to pass custom strings like in the following snippet:

DateTime.Now.ToString("MM/dd/yyyy hh:mm:ss tt");

The part in between the open and close parentheses can be customized depending on the requirements.

Following is the different characters available for the custom format. This can also be seen on the MSDN website: http://msdn.microsoft.com/en-us/library/8kb3ddd4(VS.71).aspx.

The following table describes the custom format specifiers and the results they produce. The output of these format specifiers is influenced by the current culture and the settings in the Regional Options control panel.

Format specifier	Description
d	Displays the current day of the month, measured as a number between 1 and 31, inclusive. If the day is a single digit only (1-9), then it is displayed as a single digit.Note that if the 'd' format specifier is used alone, without other custom format strings, it is interpreted as the standard short date pattern format specifier. If the 'd' format specifier is passed with other custom format specifiers or the '%' character, it is interpreted as a custom format specifier.
dd	Displays the current day of the month, measured as a number between 1 and 31, inclusive. If the day is a single digit only (1-9), it is formatted with a preceding 0 (01-09).
ddd	Displays the abbreviated name of the day for the specified DateTime. If a specific valid format provider (a non-null object that implements IFormatProvider with the expected property) is not supplied, then the AbbreviatedDayNames property of the DateTimeFormatand its current culture associated with the current thread is used. Otherwise, theAbbreviatedDayNames property from the specified format provider is used.
dddd (plus any number of additional "d" characters)	Displays the full name of the day for the specified DateTime. If a specific valid format provider (a non-null object that implements IFormatProvider with the expected property) is not supplied, then the DayNames property of the DateTimeFormat and its current culture associated with the current thread is used. Otherwise, the DayNames property from the specified format provider is used.
f	Displays seconds fractions represented in one digit.Note that if the 'f' format specifier is used alone, without other custom format strings, it is interpreted as the full (long date + short time) format specifier. If the 'f' format specifier is passed with other custom format specifiers or the '%' character, it is interpreted as a custom format specifier.
ff	Displays seconds fractions represented in two digits.
fff	Displays seconds fractions represented in three digits.
ffff	Displays seconds fractions represented in four digits.
fffff	Displays seconds fractions represented in five digits.
ffffff	Displays seconds fractions represented in six digits.
fffffff	Displays seconds fractions represented in seven digits.
g or gg (plus any number of additional "g" characters)	Displays the era (A.D. for example) for the specified DateTime. If a specific valid format provider (a non-null object that implements IFormatProvider with the expected property) is not supplied, then the era is determined from the calendar associated with theDateTimeFormat and its current culture associated with the current thread.Note that if the 'g' format specifier is used alone, without other custom format strings, it is interpreted as the standard general format specifier. If the 'g' format specifier is passed with other custom format specifiers or the '%' character, it is interpreted as a custom format specifier.
h	Displays the hour for the specified DateTime in the range 1-12. The hour represents whole hours passed since either midnight (displayed as 12) or noon (also displayed as 12). If this format is used alone, then the same hour before or after noon is indistinguishable. If the hour is a single digit (1-9), it is displayed as a single digit. No rounding occurs when displaying the hour. For example, a DateTime of 5:43 returns 5.
hh, hh (plus any number of additional "h" characters)	Displays the hour for the specified DateTime in the range 1-12. The hour represents whole hours passed since either midnight (displayed as 12) or noon (also displayed as 12). If this format is used alone, then the same hour before or after noon is indistinguishable. If the hour is a single digit (1-9), it is formatted with a preceding 0 (01-09).
H	Displays the hour for the specified DateTime in the range 0-23. The hour represents whole hours passed since midnight (displayed as 0). If the hour is a single digit (0-9), it is displayed as a single digit.
HH, HH (plus any number of additional "H" characters)	Displays the hour for the specified DateTime in the range 0-23. The hour represents whole hours passed since midnight (displayed as 0). If the hour is a single digit (0-9), it is formatted with a preceding 0 (01-09).
m	Displays the minute for the specified DateTime in the range 0-59. The minute represents whole minutes passed since the last hour. If the minute is a single digit (0-9), it is displayed as a single digit.Note that if the 'm' format specifier is used alone, without other custom format strings, it is interpreted as the standard month day pattern format specifier. If the 'm' format specifier is passed with other custom format specifiers or the '%' character, it is interpreted as a custom format specifier.
mm, mm (plus any number of additional "m" characters)	Displays the minute for the specified DateTime in the range 0-59. The minute represents whole minutes passed since the last hour. If the minute is a single digit (0-9), it is formatted with a preceding 0 (01-09).
M	Displays the month, measured as a number between 1 and 12, inclusive. If the month is a single digit (1-9), it is displayed as a single digit.Note that if the 'M' format specifier is used alone, without other custom format strings, it is interpreted as the standard month day pattern format specifier. If the 'M' format specifier is passed with other custom format specifiers or the '%' character, it is interpreted as a custom format specifier.
MM	Displays the month, measured as a number between 1 and 12, inclusive. If the month is a single digit (1-9), it is formatted with a preceding 0 (01-09).
MMM	Displays the abbreviated name of the month for the specified DateTime. If a specific valid format provider (a non-null object that implements IFormatProvider with the expected property) is not supplied, the AbbreviatedMonthNames property of the DateTimeFormatand its current culture associated with the current thread is used. Otherwise, theAbbreviatedMonthNames property from the specified format provider is used.
MMMM	Displays the full name of the month for the specified DateTime. If a specific valid format provider (a non-null object that implements IFormatProvider with the expected property) is not supplied, then the MonthNames property of the DateTimeFormat and its current culture associated with the current thread is used. Otherwise, the MonthNames property from the specified format provider is used.
s	Displays the seconds for the specified DateTime in the range 0-59. The second represents whole seconds passed since the last minute. If the second is a single digit (0-9), it is displayed as a single digit only.Note that if the 's' format specifier is used alone, without other custom format strings, it is interpreted as the standard sortable date/time pattern format specifier. If the 's' format specifier is passed with other custom format specifiers or the '%' character, it is interpreted as a custom format specifier.
ss, ss (plus any number of additional "s" characters)	Displays the seconds for the specified DateTime in the range 0-59. The second represents whole seconds passed since the last minute. If the second is a single digit (0-9), it is formatted with a preceding 0 (01-09).
t	Displays the first character of the A.M./P.M. designator for the specified DateTime. If a specific valid format provider (a non-null object that implements IFormatProvider with the expected property) is not supplied, then the AMDesignator (or PMDesignator) property of the DateTimeFormat and its current culture associated with the current thread is used. Otherwise, the AMDesignator (or PMDesignator) property from the specifiedIFormatProvider is used. If the total number of whole hours passed for the specifiedDateTime is less than 12, then the AMDesignator is used. Otherwise, the PMDesignator is used.Note that if the 't' format specifier is used alone, without other custom format strings, it is interpreted as the standard long time pattern format specifier. If the 't' format specifier is passed with other custom format specifiers or the '%' character, it is interpreted as a custom format specifier.
tt, tt (plus any number of additional "t" characters)	Displays the A.M./P.M. designator for the specified DateTime. If a specific valid format provider (a non-null object that implements IFormatProvider with the expected property) is not supplied, then the AMDesignator (or PMDesignator) property of the DateTimeFormatand its current culture associated with the current thread is used. Otherwise, theAMDesignator (or PMDesignator) property from the specified IFormatProvider is used. If the total number of whole hours passed for the specified DateTime is less than 12, then theAMDesignator is used. Otherwise, the PMDesignator is used.
y	Displays the year for the specified DateTime as a maximum two-digit number. The first two digits of the year are omitted. If the year is a single digit (1-9), it is displayed as a single digit.Note that if the 'y' format specifier is used alone, without other custom format strings, it is interpreted as the standard short date pattern format specifier. If the 'y' format specifier is passed with other custom format specifiers or the '%' character, it is interpreted as a custom format specifier.
yy	Displays the year for the specified DateTime as a maximum two-digit number. The first two digits of the year are omitted. If the year is a single digit (1-9), it is formatted with a preceding 0 (01-09).
yyyy	Displays the year for the specified DateTime, including the century. If the year is less than four digits in length, then preceding zeros are appended as necessary to make the displayed year four digits long.
z	Displays the time zone offset for the system's current time zone in whole hours only. The offset is always displayed with a leading sign (zero is displayed as "+0"), indicating hours ahead of Greenwich mean time (+) or hours behind Greenwich mean time (-). The range of values is –12 to +13. If the offset is a single digit (0-9), it is displayed as a single digit with the appropriate leading sign. The setting for the time zone is specified as +X or –X where X is the offset in hours from GMT. The displayed offset is affected by daylight savings time.
zz	Displays the time zone offset for the system's current time zone in whole hours only. The offset is always displayed with a leading or trailing sign (zero is displayed as "+00"), indicating hours ahead of Greenwich mean time (+) or hours behind Greenwich mean time (-). The range of values is –12 to +13. If the offset is a single digit (0-9), it is formatted with a preceding 0 (01-09) with the appropriate leading sign. The setting for the time zone is specified as +X or –X where X is the offset in hours from GMT. The displayed offset is affected by daylight savings time.
zzz, zzz (plus any number of additional "z" characters)	Displays the time zone offset for the system's current time zone in hours and minutes. The offset is always displayed with a leading or trailing sign (zero is displayed as "+00:00"), indicating hours ahead of Greenwich mean time (+) or hours behind Greenwich mean time (-). The range of values is –12:00 to +13:00. If the offset is a single digit (0-9), it is formatted with a preceding 0 (01-09) with the appropriate leading sign. The setting for the time zone is specified as +X or –X where X is the offset in hours from GMT. The displayed offset is affected by daylight savings time.
:	Time separator.
/	Date separator.
"	Quoted string. Displays the literal value of any string between two quotation marks preceded by the escape character (/).
'	Quoted string. Displays the literal value of any string between two " ' " characters.
%c	Where c is both a standard format specifier and a custom format specifier, displays the custom format pattern associated with the format specifier.Note that if a format specifier is used alone as a single character, it is interpreted as a standard format specifier. Only format specifiers consisting of two or more characters are interpreted as custom format specifiers. In order to display the custom format for a specifier defined as both a standard and a custom format specifier, precede the specifier with a % symbol.
\c	Where c is any character, the escape character displays the next character as a literal. The escape character cannot be used to create an escape sequence (like "\n" for new line) in this context.
Any other character	Other characters are written directly to the result string as literals.

Crystal Reports for Web Paging Problem

2010-08-31T20:42:00.000-07:00

Noticed how the paging of Crystal Reports for Visual Studio works, that when the report is more than 2 pages, the navigator gets stuck at page 2?

Here's a simple solution.
If the ReportDocument loading codes are placed in the Page_Load event of the page...

protected void Page_Load(object sender, EventArgs e)
{
   .
   .
   .
   ReportViewer.ReportSource = reportDocument;
}

...create a new Page_Init event and move the codes there.

protected void Page_Init(object sender, EventArgs e)

{

ReportViewer.ReportSource = reportDocument;

}

Now the paging will work as intended.

-elyk

IIS 6.0 and Session State Problems

2010-05-13T20:02:00.000-07:00

Have you tried publishing a website in a development server without problems only to see them once deployed on a production server? Here's one problem you might encounter. Why does the session expire quickly when you explicitly set the timeout property in the website's web.config?

Here's a good post that explains why: WHY DO I LOSE ASP SESSION STATE ON IIS6

Now after digesting the post, I'll give a simple solution you may try to solve that problem.

Step 1:

Change the sessionState in the web.config to an out of process like StateServer.

We'll use the StateServer mode which is ASP.NET's special session handling method. Don't change the stateConnectionString, that is simply the port that will be used by the ASP.NET State Service.

Step 2:

Now let's configure the ASP.NET State Service.

In the server hosting the website, go to Start > Run > Type services.msc

Select ASP.NET State Service and right click it and select Properties.

Make sure to select Automatic in Startup type, so the service will start automatically everytime the server reboots. Then start the service.

Step 3:

Now try running the website and see if it already follows the timeout period you set in the web.config. If it does and you haven't encountered any problems then all is good, congrats!. But if you encountered this sneaky error:

Sys.WebForms.PageRequestManagerServerErrorException: An unknown error occurred while processing the request on the server. The status code returned from the server was: 500

Then your problem might be serialization. Because sessions that will be saved in the ASP.NET State Service must be serialized. Two things to make sure is to first serialize all your local classes like this:

[Serializable]
public class SampleClass
{

}

Place a Serializable tag before the declaration of the class.

Second is to make sure you're not using classes that cannot be serialized like Web Controls (Button, Textbox, Table, etc.). Just search msdn for other non-serializable classes.

If you followed these steps your website should be running okay by now.

Here's some topics you might be interested:
Session-State Modes
Serialization

-elyk

ASP.NET Enable Session in Web Service Methods

2010-04-17T08:50:00.000-07:00

Ever tried accessing session variables in Web Service methods? It won't work unless you add a little property in the WebMethod header of the functions.

For example, the basic hello world:

[WebMethod(EnableSession=true)]
public void HelloWorld()
{
...
}

Just add the statement EnableSession=true and you'll be able to access session variables found normally in aspx pages like the following sample.

string userid = Session["userid"].ToString();

ASP.NET C# Set Value to Password Textbox in Code Behind

2010-04-15T19:39:00.000-07:00

If ever you've tried setting value in code-behind to a textbox with TextMode property set to "Password", you would notice it doesn't display the masked text on the page. This is simply the way it is for security purposes, but there is a workaround so you can show the user there is actually text in the textbox.

Here is the snippet:

txt1.Text = "sample_password";

if (txt1.TextMode == TextBoxMode.Password)
{
txt1.Attributes.Add("value", txt1.Text);
}

Just set the same text value to the javascript attribute "value" and you're done.

Javascript OnLoad Page Resize and Move to Center

2010-04-13T01:46:00.000-07:00

Here's a snippet for loading a web page with set width and height and moving it at the center of the screen.

window.onload = function() {
   var width = 800;
   var height = 600;
   window.resizeTo(width, height);
   window.moveTo(((screen.width - width) / 2), ((screen.height - height) / 2));
}

For this sample we resize the window to 800 by 600 and then placed it at the center of the screen by taking the screen width and height (current monitor resolution) then subtracting it with the set width and height (800 and 600 respectively) and finally diving it by 2. Now, simply place this script on the head part of the page and that's it.

Disable Refresh in Webpage Using Javascript (F5 & Ctrl + R)

2010-04-06T19:27:00.000-07:00

Okay here's another script for disabling refresh (F5 & Ctrl + R) in your web pages.

document.onkeydown = function() {
   switch (event.keyCode) {
   case 116 : //F5 button
   event.returnValue = false;
   event.keyCode = 0;
   return false;
   case 82 : //R button
   if (event.ctrlKey) {
   event.returnValue = false;
   event.keyCode = 0;
   return false;
   }
   }
}

Same as before, you can add this to your main javascript file and place it in the head part of your page.

It works by adding a function to your page's onkeydown event. Then we simply get which button was pressed by using event.Keycode (116 for F5 and 82 for R). Also, notice the "if" statement for R, it simply checks if the control button was pressed at the same time as R by checking event.ctrlKey.

But there's a limitation to handling page refreshes with this code. You simply cannot control the refresh button specific to your browsers' toolbar.

So the only way to really prevent users to refresh the page is by using this code and at the same time opening your page at a new window without the toolbar.
Check http://codingresource.blogspot.com/2010/01/javascript-windowopen-in-net.html for more info on how to do that.

Disable Right-Click in Webpage Using Javascript

2010-04-06T18:10:00.000-07:00

Here's a simple javascript snippet you can use to disable right-click in your web pages:

document.oncontextmenu = function() {
alert('Right-click is disabled.');
return false;
}

Just place the above code anywhere in your main javascript file or in the head part of the main page. You can also remove or change the alert if you don't want to notify the user.

AutoCompleteExtender problems with ModalPopupExtender

2010-03-04T21:55:00.000-08:00

If you've tried to use the AutoCompleteExtender inside a ModalPopupExtender, you'll notice that the autocomplete options show behind the modal popup. This is a Z-index problem in which the ModalPopupExtender overrides all other controls. If you check the modal's Z-index you'll see that it uses 100001 for its foreground element, so use something higher like 10000001.

<cc1:AutoCompleteExtender ID="ace" runat="server" OnClientShown="ShowOptions">
</cc1:AutoCompleteExtender>

<script language="javascript" type="text/javascript">
    function ShowOptions(control, args) {
        control._completionListElement.style.zIndex = 10000001;
    }
</script>

So we use the OnClientShown property which will call a javascript function to change the AutoCompleteExtender's Z-index when it kicks in.

SQL Select Into & Insert Into Select

2010-03-01T17:03:00.000-08:00

Here are two useful T-SQL query syntax for inserting select statements into tables:

SELECT INTO
SELECT table1.column1, table1.column2, table1.column3
INTO new_table
FROM table1

INSERT INTO SELECT
INSERT INTO table1
SELECT table2.column1, table2.column2, table2.column3
FROM table2

Both of these syntax inserts query results into a table, the only difference is that we use SELECT INTO to insert values from an existing table to a new one (a new table that is not yet present in the database).

And we use INSERT INTO SELECT to insert values from an existing table to another existing one. Of course be reminded that the number of select columns from the source table should match the destination table's columns. Also note that if you use SELECT INTO to copy values from an existing table to another one, you'll get an error like this: Msg 2714, Level 16, State 6 - There is already an object named 'table_name' in the database. So you really should use INSERT INTO SELECT in those cases.

ASP.NET C# OnEnter event in TextBox

2010-02-25T21:37:00.000-08:00

Here is a workaround for ASP.NET C# if you want an event that triggers on pressing the "Enter" key on your keyboard while still inside a textbox.

First the javascript snippet:

if (event.which || event.keyCode) {
   if ((event.which == 13) || (event.keyCode == 13)) {
   document.getElementById('btnClick').click();
   return false;
   }
}
else {
   return true;
};

It just captures the "Enter" key press (which is 13) and then clicks the corresponding button to trigger its event. So you just place this script on the textbox's onkeydown attribute which I'll show in just a sec.

protected void Page_Load(object sender, EventArgs e)
{
   if (!IsPostBack)
   {
   txtBox.Attributes.Add("onkeydown", "if(event.which || event.keyCode){if ((event.which == 13) || (event.keyCode == 13)) {document.getElementById('" + btnClick.UniqueID + "').click();return false;}} else {return true}; ");
   }
}

Just add the attribute on the Page_Load event and you're done.

Check this link for more keycodes: http://www.cambiaresearch.com/c4/702b8cd1-e5b0-42e6-83ac-25f0306e3e25/Javascript-Char-Codes-Key-Codes.aspx

-k

ASP.NET C# : Working With Cookies

2010-02-25T20:19:00.000-08:00

If enabled on client browsers, cookies are a great way to store bits of data for use by websites like remembering the login state of users who doesn't want to retype their username and password everytime they visit the site.

Here are the most common functions you can use to manipulate cookies in ASP.NET (C#):

SETCOOKIE
public void SetCookie(string name, string value, int expiration)
{
   HttpCookie cookie;
   if (Request.Cookies[name] == null) cookie = new HttpCookie(name);
   else cookie = Request.Cookies[name];
   cookie.Value = value;
   cookie.Expires = DateTime.Now.AddDays(expiration);
   Response.Cookies.Add(cookie);
}

SetCookie can be used to add a new cookie or overwrite an exisiting one in your cookie collection. Simply pass the name and value pair and the expiration (in days) for how long you want that cookie to be in use by your website. In the following code, we store the username "abby" in our collection for 1 day.

SetCookie("username", "abby", 1);

Take note though that if you use the same cookie name "username" again to set another value, it will overwrite the previous one.

GETCOOKIE
public string GetCookie(string name)
{
   HttpCookie cookie = Request.Cookies[name];
   if (cookie == null) return "";
   else return cookie.Value;
}

GetCookie can be used to retrieve the value of the cookie by passing the name. In the following code, we get the value of the cookie considering it has not yet expired.

string str = GetCookie("username");

DELETECOOKIE
public void DeleteCookie(string name)
{
   HttpCookie cookie;
   if (Request.Cookies[name] == null) return;
   else cookie = Request.Cookies[name];
   cookie.Expires = DateTime.Now.AddDays(-1);
   Response.Cookies.Add(cookie);
}

DeleteCookie can be used to delete a particular cookie from the cookie collection by passing the name. Notice the -1 in the AddDays? That will simply delete the value in the physical cookie file. In the following code, we delete the "username" cookie.

DeleteCookie("username");

CLEARCOOKIES
public void ClearCookies()
{
   int cookieCount = Request.Cookies.Count;

   for (int i = 0; i < cookieCount; i++)
   {
   HttpCookie cookie = Request.Cookies[i];
   cookie.Expires = DateTime.Now.AddDays(-1);
   Response.Cookies.Add(cookie);
   }
}

ClearCookies can be used to delete all cookies in the cookie collection. We also used the -1 in the AddDays here but used a loop to delete each one in the collection. In the following code, it will delete the physical cookie file of your website.

ClearCookies();

And that's it for cookies.

-k

IIS7 Publish Problems with Database

2010-02-13T08:02:00.000-08:00

So after testing your website on Visual Studio and made sure everything is working fine, especially database connections, you now published your new site on IIS7 and to your surprise connections don't work as you've set. Try these following steps..

Open IIS by going to Control Panel > Administrative Tools > Internet Information Services (IIS) Manager. On the left menu, click on Application Pools.

Click on DefaultAppPool and then Advanced Settings...

Click on the Identity selector under Process Model.

Change it to LocalSystem and click Ok.

Now try running your website again and it should have no more connection problems.

-k

Get Client MAC Address & IP Address using Javascript

2010-02-11T07:01:00.000-08:00

This is somewhat similar to the previous post Get client cpu id with javascript, so the client still needs to enable ActiveX components on his browser. Read more on the said post for details.

Ok if you're done reading, you'll notice we simply change the script to this:

<script type="text/javascript">
    var macAddress = "";
    var ipAddress = "";
    var computerName = "";
    var wmi = GetObject("winmgmts:{impersonationLevel=impersonate}");
   e = new Enumerator(wmi.ExecQuery("SELECT * FROM Win32_NetworkAdapterConfiguration WHERE IPEnabled = True"));
    for(; !e.atEnd(); e.moveNext()) {
        var s = e.item();
        macAddress = s.MACAddress;
        ipAddress = s.IPAddress(0);
        computerName = s.DNSHostName;
    }
</script>

Instead of Win32_Processor, here we'll access Win32_NetworkAdapterConfiguration to read network related details like the MAC Address, IP Address and the computer name.

Then we can simply use textboxes to display that information or whatever you like.

<input type="text" id="txtMACAdress" />
<input type="text" id="txtIPAdress" />
<input type="text" id="txtComputerName" />

<script type="text/javascript">
    document.getElementById("txtMACAdress").value = unescape(macAddress);
    document.getElementById("txtIPAdress").value = unescape(ipAddress);
    document.getElementById("txtComputerName").value = unescape(computerName);
</script>

And just like before, make sure to place the declarations snippet above this script for it to display the values properly. Now the client can see his/her own MAC and IP Addresses.

Read more about the Win32_NetworkAdapterConfiguration object here http://msdn.microsoft.com/en-us/library/aa394217(VS.85).aspx

-k

ASP.NET AJAX this._form is null error on javascript

2010-02-10T23:59:00.000-08:00

If ever you encounter this sneaky error on your ASP.NET AJAX-Enabled websites (you would know it when you see the this._form is null javascript error message or simply if your controls don't cause postbacks anymore) the culprit is the javascript declaration found on the head tag in the html page.

If you have declared it like this:

<script src="scripts/main.js" type="text/javascript" />

Simply change it to this:

<script src="scripts/main.js" type="text/javascript"></script>

And problem is solved.

-k

ASP.NET Logout on Session Expire

2010-01-31T22:39:00.000-08:00

Here's a way to enable logout after session has expired in your ASP.NET pages.

Let us begin with the sessionState tag inside the web.config file:

<system.web>
   <sessionState mode="InProc" cookieless="false" timeout="30"/>
</system.web>

Make sure to place it inside the system.web tag. For the attributes, we use InProc mode to store the session on the local computer, cookieless is set to false which means it will store the session as cookies (if you set this to true, you will get some jumbled alphanumeric characters in your webpage's URL) and finally timeout which has a numeric value equal to how long you want your session in minutes before it expires.

For more information on sessionState attributes, check out msdn: http://msdn.microsoft.com/en-us/library/h6bb9cz9(VS.71).aspx

Now the snippet above alone will not make your page redirect automatically to your logout page after session has expired. We still need human intervention to enable that. So we add this next logic to the Master Page's page_load event (or to all pages of a website if you're not using master pages):

protected void Page_Load(object sender, EventArgs e)
{
   //1st: Every postback should pass through this code.
   // Make a decision statement to check if user has already logged in.
   if (user has already logged in)
   {
   //2nd: Check your user session.
   If session is null (expired) then continue.
   if (Session["user_session"] == null)
   {
   //3rd: Clear all sessions, data, connections, etc. (optional)
   Redirect to logout page.
   .
   .
   .
   Page.Response.Redirect("logout_page", true);
   }
   }
}

Handling session expiration is required for web pages which uses sessions to store data so you won't encounter the object reference not set to an instance of an object error should your session objects expire.

-k

ASP.NET Server tag was not well formed

2010-01-31T05:51:00.000-08:00

TIP: ASP.NET C# Expression Language with Javascript

Here's a tip on how to use C# bind code inline with javascript events, first let's use a LinkButton for example:

<asp:LinkButton ID="lnkBtn" runat="server" OnClick="lnkBtn_Click" OnClientClick='<%# "document.getElementById(\"txtHtmlText\").value = " + Eval("id") + ";" %>' />

Imagine this LinkButton is inside a binded control like Gridview or Repeater, etc., now look at the OnClientClick attribute. Remember to be careful with single and double quotes.

1. Use single quotes to contain the whole expresion.

          OnClientClick='  ... '

2. Enclose inner javascript statements with double quotes and concatenate it with .NET bind statements (like Eval()) with the "+" symbol.

          "document.getElementById(\"txtHtmlText\").value = " + Eval("id") + ";"

3. Use escaped double quotes (the one with the slash) if ever you'll use double quotes inside another one.

          getElementById(\"txtHtmlText\")

So the next time you get the error "Server tag was not well formed" just remember these 3 tips.

-k

Change Web Service name in ASP.NET

2010-01-28T23:53:00.000-08:00

For example you have a Web Service named AAAWebService

And you want to change its name to let's say BBBWebService. If you open your code and change it like this..

public class BBBWebService : System.Web.Services.WebService

{

}

... and then run it, you would get an error like this...

The solution is to right click on your web service asmx file and click view markup.

Change the name here and you're done.

<%@ WebService Language="C#" CodeBehind="AAAWebService.asmx.cs" Class="Web_Services.BBBWebService" >

-k

ASP.NET C# Refresh page from code behind

2010-01-28T18:33:00.000-08:00

To refresh your page you may use the javascript function:

window.location.reload();

For example you can use that on the OnClientClick attribute of an ASP.NET button:

<asp:button ID="btnRefresh" OnClick="btnRefresh_Click" runat="server" Text="REFRESH"
OnClientClick="window.location.reload();" />

The code above will work fine, but if let's say you have some other server-side logic you want to run on the code for btnRefresh_Click, it won't be executed because the page would already be refreshed by then.

So to run your server-side code, first remove the OnClientClick attribute on the asp button tag above. Then place the following code inside your button click event:

protected void btnRefresh_Click(object sender, EventArgs e)
{
//Your logic here...
Page.Response.Redirect(HttpContext.Current.Request.Url.ToString(), true);
}

We simply redirect the page to its current url and that does the trick.

-k

Javascript Window.Open() in .NET

2010-01-27T03:58:00.000-08:00

Here's an example on how to popup a new window using javascript in .NET. First we'll use a simple button as the trigger source for the popup.

<asp:Button ID="btnPopup" runat="server" />

Then on the page load in the code behind, add an onclick attribute to the button.

protected void Page_Load(object sender, EventArgs e)
{
btnPopup.Attributes.Add("onclick", "window.open('http://" + Page.Request.Url.Authority + "/TestPage.aspx','Test','status,toolbar,location,menubar,directories,resizable,scrollbars,width=400,height=400')");
}

The Page.Request.Url.Authority in the code above will retrieve the root url of your site. Then just add the name of the aspx file to popup after the forward slash (if it is within another directory, just add the directory name before the aspx file, and so forth).

To explain the javascript part, window.open() accepts 3 parameters: the url of the site to popup, the window name (not title, the title should be in the head part of the new page, so make sure it doesn't have spaces), and window features.

Here's some of the commonly used window features:

status:

toolbar:

location:

menubar:

directories:

resizable: window can be resized

scrollbars:

width: the width of the window in pixels

height: the height of the window in pixels

To use these features simply add them to the list like this:

"window.open
('http://www.testpage.com','Test','status,toolbar,location,menubar,directories,resizable,scrollbars,width=400,height=400')"

If not then simply omit them:

"window.open('http://www.testpage.com','Test','width=400,height=400')"

That's it, one note though, make sure that the aspx page in the url exists or you'll get an error.

-k

Login failed for user 'NT AUTHORITY\IUSR'

2010-01-25T05:47:00.000-08:00

If you encountered this error while running your published website or web service in IIS7:

Message: Sys.WebForms.PageRequestManagerServerErrorException: Cannot open database "[DB_NAME]" requested by the login. The login failed.

Just follow these simple steps to solve the problem.

1. Open SQL Server Management Studio.

2. On the left menu, expand Security then Logins. Check if 'NT AUTHORITY\IUSR' exists. If not then that is the cause of the problem.

3. Right-click on Logins then click New Login...

4. On the General page, click Search...

5. On the next popup window, click Advanced...

6. Then on the following window, click Find Now and find IUSR on the Search Results. Then click OK.

7. Back on the left menu, you'll now see the 'NT AUTHORITY\IUSR' user. Right click on it and click Properties.

8. On the Server Roles page, check on sysadmin.

9. Then on the User Mapping page check on the database name you need access to; and below that on the database role membership make sure to also check on db_owner then click OK.

...And that's a wrap, you shouldn't be seeing the login failed error now.

-k

Internet Explorer 6 for Windows Vista / Windows 7

2010-01-22T18:38:00.000-08:00

If you're running on Vista or Windows 7 it's sure you're IE browser is already IE7 or IE8, but suppose you're developing for clients who will still use the "buggy" IE6 (so it simply means you have to develop sites which takes those bugs into consideration), one way is to install a Virtual Machine on your PC that will run Windows XP which will surely use much of your PC's resources (hard drive space and memory). The other is this program I found called IETester. Check it out here.

It's still an alpha release so there might be bugs here and there but it will only take you a minute to download its 25mb filesize and it's free. Now you can live with those cross-browser compatibility issues all over again, one of those I will be tackling on my next post so keep tuned.

-k

How to use events like onblur, onfocus, etc. for ASP.NET Texbox and other controls

2010-01-22T07:53:00.000-08:00

Have you ever wondered if you can use other event attributes for some ASP.NET controls, say an ASP.NET Textbox?

When upon checking, all you see that's available is a TextChanged event. And you know that the html input tag can support other events like:

Source: w3schools

A workaround is to create an ASP.NET Button and place it inside a hidden div:

<div style="display: none;">
    <asp:Button ID="btnTextBoxEventHandler" runat="server"
    OnClick="btnTextBoxEventHandler_Click" />
</div>

And here's the markup for the textbox, just a regular one:

<asp:Textbox ID="txt1" runat="server" />

Now on your page onload event, add an attribute to your textbox:

protected void Page_Load(object sender, EventArgs e)
{
    txt1.Attributes.Add("onblur", this.Page.ClientScript.GetPostBackEventReference(this.btnTextBoxEventHandler, ""));
}

Then of course, the event handler for the button:

protected void btnTextBoxEventHandler_Click(object sender, EventArgs e)
{
    //Place code here for onblur..
}

Now place the code you want to trigger (when the textbox loses focus) inside the button event and see what happens. Try experimenting with other event attributes and ASP.NET control combinations too.

-k

Visual Studio Line Numbers

2010-01-21T22:36:00.000-08:00

Ever wondered why errors in Visual Studio show you line numbers where it occured yet upon checking back on your code you found none? That is because by default, on installation of Visual Studio, line numbers are disabled. To enable it simply go to menu then tools then options.

Once the options window pop up, expand on Text Editor and select the language you want to show line numbers and simply click the checkbox "Line numbers".

You can do this to other languages you want, better if you do it on all.

That's it, the only thing I've been wondering is why Microsoft opted to disable it by default when we all know that line numbers are important for debugging..

-k

Get Client CPU ID with Javascript

2010-01-21T21:53:00.000-08:00

For whatever purpose it may serve, here's how to get the client CPU ID through javascript. Just a warning though, this script uses ActiveX object which is disabled by default on browsers and I'm not sure if you can enable it on non-IE. So for now we'll just do it with Internet Explorer.

Go to Tools then Internet Options.

Then on the Security tab click on "Custom Level..."

Go down until you see "Initialize and script ActiveX controls not marked as safe..." and enable it then click Ok.

Now we go to the scripting part. Add this next snippet in your html page.

<script type="text/javascript">
   var str = "";
   var wmi = GetObject("winmgmts:{impersonationLevel=impersonate}");
   e = new Enumerator(wmi.InstancesOf("Win32_Processor"));
   for(; !e.atEnd(); e.moveNext()) {
   var s = e.item();
   str = s.ProcessorID;
   }
</script>

You can add the script above anywhere on your html head or body, but if you chose to put it on the body be sure to place it anywhere above this next snippet, which just displays the CPU ID in the page.

<b>Client CPU ID : </b><span id="spanCPUID" />

<script type="text/javascript">
   document.getElementById("spanCPUID").innerHTML = str;
</script>


And that's it, you should now see the client computer's cpu id when you run the page.

-k