The next account in asp.net does not allow multiple users to log on online at the same time.

Method 1:

Copy codeThe Code is as follows: string sKey = username. Text. ToString (). Trim (); // obtain the value of the given Key in the Cache.
String sUser = Convert. ToString (Cache [sKey]); // check for existence
If (sUser = null | sUser = String. Empty)
{
TimeSpan SessTimeOut = new TimeSpan (0, 0, System. Web. HttpContext. Current. Session. Timeout, 0, 0); // get the Session expiration time
HttpContext. current. cache. insert (sKey, sKey, null, DateTime. maxValue, SessTimeOut, System. web. caching. cacheItemPriority. notRemovable, null); // put the value into the cache to facilitate single-point Login
// Login successful
}
Else if (Cache [sKey]. ToString () = sKey) // if this account has been logged on
{
ClientScript. RegisterStartupScript (GetType (), "prompt", "<script> alert ('Sorry, the current user has logged on '); </script> ");
Return;
}
Else
{
Session. Abandon (); // This section is mainly used to prevent unnecessary errors and cause logon failure.
}

Copy codeThe Code is as follows: // how to clear the Cache when closing the browser or window. Add an onunload Event to the aspx file on the home page. Clear Session. SessionID in hOnline through ajax.
Window. onunload = function (){
$. Ajax ({
Type: "POST ",
Data: "sKey =" + sKey;
Url: "online. aspx"
});
}

Online. aspx. cs codeCopy codeThe Code is as follows: protected void Page_Load (object sender, EventArgs e)
{
HttpContext. Current. Cache. Remove (sKey );
}
// Add the Session_End method in the Global. asax File
// After the Session expires, clear the Session. SessionID in hOnline.
Hashtable hOnline = (Hashtable) Application ["Online"];
If (hOnline [Session. SessionID]! = Null)
{
HOnline. Remove (Session. SessionID );
Application. Lock ();
Application ["Online"] = hOnline;
Application. UnLock ();
}

Method 2: Copy codeThe Code is as follows: // sKey is the logon User Name
If (ApplicationOnline (username. Text. tirm ())){
Hashtable hOnline = new Hashtable ();
HOnline [Session. SessionID] = sKey;
Application. Lock ();
Application ["Online"] = hOnline;
Application. UnLock ();
}

Public Boolean ApplicationOnline (string sKey)
{
Boolean flag = true;
Hashtable hOnline = (Hashtable) Application ["Online"];
If (hOnline! = Null)
{
IDictionaryEnumerator idE = hOnline. GetEnumerator ();
While (idE. MoveNext ())
{
// If (idE. Key! = Null & idE. Key. ToString (). Equals (Session. SessionID ))
//{
If (idE. Value! = Null & sKey. Equals (idE. Value. ToString ()))
{
Flag = false;
}
Break;
//}
}
}
Return flag;
}

// Clear Session. SessionID when closing the browser or window. Add an onunload Event to the aspx file on the home page. Clear Session. SessionID through ajax.
Window. onunload = function (){
$. Ajax ({
Type: "POST ",
Url: "online. aspx"
});
}

Online. aspx. cs codeCopy codeThe Code is as follows: protected void Page_Load (object sender, EventArgs e)
{
Hashtable hOnline = (Hashtable) Application ["Online"];
If (hOnline [Session. SessionID]! = Null)
{
HOnline. Remove (Session. SessionID );
Application. Lock ();
Application ["Online"] = hOnline;
Application. UnLock ();
}
}