Windows Phone : How to set Startup/Default page

Issue: How to set Startup / Default page in Windows Phone 7/8 app.

Solution:
Open WMAppManifest.xml file in Properties folder.
Set the proper Page name for the Tasks/DefaultTask/NavigationPage attribute as below:

<Tasks>
      <DefaultTask  Name ="_default" NavigationPage="Page1.xaml"/>
</Tasks>

How to get File Extension from File Name - C#,ASP.NET

Issue:
How to get File Extension from File Name - C#,ASP.NET

Solution:
System.IO.Path.GetExtension(filename);

Example:
string fileName = @"C:\temp\mypic.jpg";
extension = Path.GetExtension(fileName);
Console.WriteLine("Extension:"+extension);

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ASP.NET Session.Abandon() doesn't work - not Logged out

Issue:
Calling Session.Abandon() does not clear the full session and invalidate the login. User is not logged out by this.

Details:
Session.Abandon() Clears the current session of the user. This does not specifically ensures to clear all Session. For that you need to specifically call the Session.Clear() method. But many users expect to logout the user after these methods are called, which doesn't work well. Also this server side method doesn't clear the cached session on the client browser.

Solution:
If you want to invalidate the user login, the best solution is to use the ASP.NET LoginStatus control.

<asp:LoginStatus id="LoginStatus1" runat="server" LogoutAction="RedirectToLoginPage" />

Make sure to set the LogoutAction property to "RedirectToLoginPage". This will invalidate the user's session and Log him out.

Unable to update the EntitySet - because it has a DefiningQuery and no element exists in the element to support the current operation.

Error:
Unable to update the EntitySet 'Classroom' because it has a DefiningQuery and no <InsertFunction> element exists in the <ModificationFunctionMapping> element to support the current operation.

This error is raised while using Entity Framework.
While trying to save and persist db changes it raise this error. This error happens only in particular save and not every other places. The save operation raising this error is most probably an insert or a delete operation; like or example in my case:

db.Classrooms.Add(classroom);
db.SaveChanges();

Cause:
Eventhought the error message is a bit cryptic, the cause of the issue is simpler. The reason for this error is because the Primary key for the table is not set.

Solution:
Set the Primary key for the table and update the Entity Model (edmx file). This should clear the "Unable to update the EntitySet - because it has a DefiningQuery and no element exists in the element to support the current operation." exception.

LINQ : How to check if a record exists in the database

Issue: How to check if a record exists in the database using LINQ

// Solution 1: Select . Don't use SingleOrDefault because if there are more than one record returned it throws exception.
var res = (from cls in db.Classrooms
                 where cls.Name == "10A"
                 select cls).SingleOrDefault();
                
if(res != null)
{
    //record exists
}

// Solution 2: Select Count if you don't want to load the entity. This is an efficient method but not the most efficient. The LINQ expression translates to Count(*) in SQL.
int res = (from cls in db.Classrooms
                 where cls.Name == "10A"
                 select cls).count();
                
if(res > 0)
{
    //record exists
}

// Solution 3:
Classroom cls = db.Classrooms.FirstOrDefault(cls => cls.Name == "10A");
if(cls != null) {
    // record exists
}
else {
    // record does not exist
}

// Solution 4: This is the most effective solution
// If you only want to know if such a Record exists:
// This is the most efficient as it generates an IF EXISTS SQL query
return db.Classrooms.Any(cls => cls.Name == "10A"); // true if exists
// Similar expression is:
return db.Classrooms.Where(cls => cls.Name == "10A").Any();

// Solution 5:
// If you want a count of how many such Record exists:
return db.Classrooms.Count(cls => cls.Name == "10A");

// Solution 6:
// If you want an enumeration (IEnumerable<Record>) of all such Record:
return db.Classrooms.Where(cls => cls.Name == "10A");

Open URL in Browser Programatically -IE/FF/Chrome [Windows Forms]

Problem:
I want to open a URL in desktop web browser programatically.
I want to open it in different browsers of my choice.

Solution:
Here are some code blocks to open a url in the browsers of our choice.

Below code will open a specific url in your default browser configured:
System.Diagnostics.Process.Start("http://www.habeeb.in");

To open the url in Internet Explorer, use the code:
System.Diagnostics.Process.Start("iexplore.exe", "http://www.habeeb.in");

To open the url in firefox, use the code:
System.Diagnostics.Process.Start("firefox.exe", "http://www.habeeb.in");

To open the url in Chrome, use the code:
System.Diagnostics.Process.Start("chrome.exe", "http://www.habeeb.in");







These solutions are based on Windows Desktops Winforms Applications.