问题
Here's the business problem I'm trying to solve:
Start with pages: Menu -> Activity -> Connect.
When the user navigates from Menu -> Activity, if there is a specific piece of hardware not connected, I want to immediately Navigate to the Connect page.
When back button is pressed on Connect page and there is still no device connected, we navigate back to Acitivyt. But now I do not want Activity to navigate again to Connect (trapping them in a loop). Rather I want to navigate all the way back to Menu. Prism does not (that I can find) provide a way for me to know if I'm arriving at the Activity page from the Connect page or from some other location.
In reality, Activity may be navigated to from a number of different places in the program, when they hit back on Connect, I want them to return to whatever page they came from before Activity (not necessarily Menu). What I'd like to know is how can I solve this conditional navigation problem in Prism?
来源：https://stackoverflow.com/questions/52616823/mvvm-conditional-return-navigation-in-prism