Windows Phone persistent instance of page through app life-time

Question

I am working on a simple Windows Phone app, which has basically those functionality:

• Page 1, there is a button to get user's location, and navigate to page 2
• Page 2, use the user location and map control to display a map and view center is user's location. There is a app bar button to navigate to Page 3.
• Page 3, Show some nearby place list in this page, and once user select one of the places, it will go back to page 2 to Pin the place on Map Control.

So here is the question:
I want to keep page 2 data alive in this case so I dont have to re-initialize page 2 everytime I go back from page 3. It would be perfect I can keep an instance of page 2 somewhere, and use that everytime I want to come back from page 3. So far I know there are two approach, one is in Page2 xaml I can have something like:

<Page
  x:class "Page2.keepPageAlive"
  ...

The other one is using AddBackEntry. But I am not sure which one is fit in my case, or is there any other good approach.

Please share your idea, thank you.

Answer 1

As long as you navigate to page3 from page2, and go back to page2 using NavigationService.GoBack(), the page2 instance will be kept alive. So you basically have nothing to change.

Answer 2

In the WP7 Navigation stack, Page 2 will still exist. So if you navigated from Page 1 to Page 2 to Page 3, all 3 pages exist.

If you call NavigationService.GoBack() from Page 3, it will pop Page 3 off and restore the previous instance of Page 2, not create a new instance of Page 2. This is also what happens when you hit the Back button.

Only if you call NavigationService.Navigate() would a new instance be created.