Call fucntion on App load only once

Question

Hi
I call a Windows live SDK logon function, GreetUser(); when the apps loads on start-up as below. If I navigate to another page then back again the logon calls again.
How can I make it call the function only once?
public sealed partial class GroupedPicturesPage : LayoutAwarePage
public GroupedPicturesPage()
this.InitializeComponent();
GreetUser();

Answer 1

I'm sure a real programmer would use something more sophisticated. I am a fake programmer. So, I use very simplistic solutions for this kind of thing.
In the App.xaml.cs page, create a static bool variable.  This will be your app global variable.  Initialize it to true. 
static public bool firsttime = true;
Now, in the page that you posted the code from, modify it to this.
public sealed partial class GroupedPicturesPage : LayoutAwarePage
public GroupedPicturesPage()
this.InitializeComponent();
if(firsttime==true) {
GreetUser();
App.firsttime = false;
And voila.  GreetUser() will only fire the first time around.  After that, it won't fire again.