Windows Phone Login

In this article i will write about our lessons learned - WP7 login page development.

Windows Phone apps are composed of pages that exist on a backstack and
can be reversed by user with the hardware back key.

There are some screens you do not want to come back. Like the login screen.
After successfully logged in, the login screen should removed from the backstack.
But explicit navigating away and from the login screen will cause to infinitly growing up your backstack. There are some solutions of keeping screens out of the backstack.

The Xing-App main page is a panorama control. The first approach for a login was kind of interesting.
We implement the login screen as a panorama item. This item is visible when you are not logged in. After successfully logged in, the item is hidden. The other items have the inverse behavior. 
In this solution we prevent the backstack problem.

While thinking about a different solution, we discussed the difference between transition and navigation. Navigation is a transition between different places. A Page is a place with a state.
But what is with this stateless pages? Here we have this splash screen or our login screen.
A common way to implement a login screen is as the first page of your app.

But is it really what you want?
While thinking about this, we came to that point the login screen can come up from everywhere in our app. The login screen has no place and it is stateless.

source: http://blogs.msdn.com/b/ptorr/archive/2010/08/28/introducing-the-concept-of-places.aspx

It is useful for example when you loose your access key and you have to login again.
The login page will popup at this place and you can continue after success.
The Silverlight Popup control is a great solution for showing content that (partially) covers the screen without doing a full navigation.You can also override the back key pressed event to handle the hardware back key to have more control over the popup.

This login behavior can also be useful for other platforms.