在WPF中再次导航到页面时的刷新功能

Question

In my wpf app I have two pages, page1 and page2 .

when the user go from page1 to page2 in the first time it automatically creates a new page2 .

in page1 it looks something like:

public static int someVar;
public Page1()
{
  InitializeComponent();
}
.
.
.
// the user gives some value to "someVar"
void Next_btn(object sender , RoutedEventArgs e)
{
     if (this.NavigationService.CanGoForward)
        this.NavigationService.GoForward();
     else
        NavigationService.Navigate(new Page2());
}

in page2 it looks like:

public Page2()
{
   InitializeComponent();
   if(Page1.someVar==3)
      DoSomething();
}
.
.
.
void Back_btn(object sender , RoutedEventArgs e)
{
     if (this.NavigationService.CanGoBack)
        this.NavigationService.GoBack();
}  

My problem is this:

let's say that the user done the following:

the user have been in page1 and puts someVar=2 and then goes to page2 . therefore the function DoSomething() wont be called. after that he went back to page1 and changed someVar=3 and then navigated again to page2 still the function DoSomething() wont be called(But I need that it will be called it this scenario), because it's not a new page2 .

how to solve the following scenario without navigate to a new page2 every time?

Answer 1

The code in the constructor will only be executed once for each instance of Page2.

But you could handle the Navigated event for the NavigationService in Page1 and call the DoSomething() method of Page2 in the event handler. Something like this:

void Next_btn(object sender, RoutedEventArgs e)
{
    this.NavigationService.Navigated += NavigationService_Navigated;

    if (this.NavigationService.CanGoForward)
        this.NavigationService.GoForward();
    else
        NavigationService.Navigate(new Page2());
}

private void NavigationService_Navigated(object sender, NavigationEventArgs e)
{
    var page2 = NavigationService.Content as Page2;
    if (page2 != null && someVar == 3)
        page2.DoSomething();

    this.NavigationService.Navigated -= NavigationService_Navigated;
}

Answer 2

Thanks to @8mm for his guidance, the following code worked for me:

Page2 p2=new Page2();
void Next_btn(object sender , RoutedEventArgs e)
    {

        if (this.NavigationService.CanGoForward)
        {
           p2.DoSomething();
            this.NavigationService.GoForward();
        } else
            NavigationService.Navigate(p2);
    }